These final stages are exactly what sets Isle of Raasay Distillery apart from other single malt distilleries in Scotland. All of our single malt is fully matured in our warehouses on Raasay. Once ready, these casks are vatted on site. We use water drawn directly from our own well, 60 metres below the distillery, to reduce the spirit from a cask strength of around 70% ABV down to our bottling strength of 46.4% ABV (for The Draam). This is a critical step, by adding our own well water back into the mature spirit, we reintroduce the local minerality from the geology of Raasay some of which was lost during distillation.

This localised approach is unusual. In the wider Scotch whisky industry, it is standard practice for new make spirit to be pumped into tankers holding up to 30,000 litres. This bulk spirit is then transported by road or rail to central Scotland, sometimes over 200 miles away from the distillery itself, to be reduced, filled into casks, and matured.

If you are a multinational spirits business, this centralised model makes perfect economic sense. But for us, our philosophy is different. We use our own well water to reduce the spirit and fully mature our single malt on the Hebridean island where it was fermented and distilled.

As we also bottle all of our single malt on Raasay, we have complete control over the integration of spirit and well water. In essence, nothing leaves Raasay until it is in a bottle. It is a single malt truly of the Hebridean island where it is made, shaped by the sea, The Sound of Raasay and The Inner Sound.

Disgorging and The Six Cask Recipe.

Our oak policy for The Draam is built on a very specific recipe. We mature our unpeated spirit and our heavily peated spirit separately in three distinct cask types: ex-Rye Whiskey barrels, virgin Chinkapin oak barrels, and ex-Bordeaux red wine barriques. (I go into much more detail on our oak policy in my previous post, Contemporary Scotch Whisky Making 4

After maturation, this two spirit (peated & unpeated), three cask approach gives us six components or Na Sia (The Six) in Gaelic. These six distinct flavour profiles after maturation are carefully emptied and vatted together prior to bottling The Draam.

The Process of Emptying

To remove our mature whisky, we empty the casks using either an extraction lance (essential a short length of stainless steel pipe) inserted directly through the bunghole or using our disgorging trough, which you can see in the video below.

If you watch the video closely, you will see a large amount of black charcoal sitting in the trough. We use a series of coarse filters to remove this charcoal which breaks off from the heavily toasted and charred interior walls of our casks, as well as any stray pieces of oak.

This charcoal isn’t just a by-product, it plays a crucial role in maturation. The char layer acts as an active carbon filter, a process known as adsorption. As the spirit interacts with the oak over the years, this carbon layer removes volatile impurities and sulphur compounds. This purifying effect results in a smoother, cleaner spirit especially important when bottling a single malt at a younger age.

A treat for the senses

Disgorging is a real treat for the senses. Visually, the colours are revealed highlighting the influence each cask type has on the maturation of our spirit, ranging from the straw gold of the ex-Rye barrels to the deep, autumnal copper hues imparted by the Bordeaux barriques and the deep rich mahogany colour from our Chinkapin Oak casks.

The smell of mature spirit fills the air: black pepper, vanilla & butterscotch from the ex rye barrels; BBQ, wood smoke and maple syrup from the Chinkapin oak; Dark fruit, cherries, blackcurrant and savoury spice from the ex Bordeaux red wine barriques. A prelude of the aroma of our single malt soon to be vatted and bottled.

Audibly, you can hear a distinct “glugging” noise as the casks empty. Of course this is just simple fluid dynamics in action, as the heavy liquid drops out of the cask, it creates a vacuum, forcing ambient air to rush back in through the bunghole to equalise the pressure. It is the sound of the cask finally giving up our precious single malt, a very reassuring sound indeed.

Into the Vatting Tanks

As disgorging is being completed, the spirit is pumped through to one of our three 25,000-litre stainless steel vatting tanks, which sit just outside the warehouse silhouetted against the Raasay landscape as you can see in the picture below.

You may well assume that once the required 85 to 90 casks are emptied into one of our vatting tanks that they immediately mix together. This is not the case in reality the liquid from all these different cask really does not want to mix!

These casks hold mature spirit of varying density, lipid content, and alcohol concentrations (due to the different micro-climates in our warehouses on Raasay and our three distinct cask types), as a result the liquid naturally wants to stratify.

The Art of Marrying

To address this, we start to “marrying” our spirit. For the best part of a week, our spirit is mechanically recirculated at regular intervals. This forced kinetic energy starts to bind all the complex lipid and ester chains together, slowly bring together these disparate components into a perfectly homogenous yet complex single malt.

Once this liquid still at cask strength is fully married, we draw off a portion specifically for our award winning Cask Strength bottling of The Draam.

Reduction and Reverse Osmosis

For The Draam, the spirit remaining in the vat we then start to reduce to our bottling strength of 46.4% ABV using the water from our well.

As I have already discussed this water is vital to our process, but unlike for cask reduction, it cannot be added straight from the well at this stage. First we need to run the water from the well through our Reverse Osmosis (RO) plant.

This is a result of our well water being rich in minerals (including calcium and magnesium) ideal for fermentation and cask reduction but not for bottling. If these minerals were present at this stage they would bind with the fatty acids in the whisky, causing flocculation (a permanent cloudy haze or solid precipitation in the bottle). RO is a required technical step to ensure clarity and shelf stability, even though we always bottle at a 46.4% ABV without chill filtering. I’ll discuss the importance of the % ABV in more detail in the section below on Preserving Texture.

Patience and Gentle Proofing

This reduction process takes a further week. From a chemical perspective, water and high proof ethanol do not mix instead they react with each other. Combining them triggers an exothermic reaction (releasing heat). If we were to add all the water required for reduction at once, this would “shock” the spirit, breaking the delicate ester chains and potentially causing saponification (the creation of soapy off notes). To avoid this we carry out the following:

Micro-additions: We add the RO water in small increments of just a few hundred litres at a time.

Preventing Stratification: Because water is denser than alcohol, it naturally sinks. We recirculate the tank thoroughly between every single addition.

Homogenisation: This slow, progressive reduction allows the water to bind with the ethanol molecules, ensuring homogeneity prior to bottling.

Preserving Texture & Mouthfeel

A critical technical detail worth noting, we never chill filter our single malt.

In much of the commercial Scotch whisky industry, chill filtration is standard practice. Before bottling, the whisky is chilled down to around 0°C and pumped through a series of tightly packed filters. The sudden drop in temperature forces the natural fatty acids, proteins and long-chain esters in the whisky to clump together (micelle formation) allowing them to be easily filtered out.

Why do this? Purely for aesthetics. If a whisky is not chill filtered, it can develop a temporary cloudiness, known as a “chill haze”, if a customer drops an ice cube into their glass or stores their bottle in a cold room.

However in my opinion removing these comes at an extremely heavy cost. These natural fatty acids, proteins, and long-chain esters are responsible for our whisky’s rich mouthfeel, viscosity, its complex and lingering finish. By choosing not to chill filter we are intentionally retain all of the texture, oiliness, and flavour keeping it in our single malt we have painstakingly created and ultimately where it belongs, in your glass.

After all, as you will have read in my other posts we go to great lengths to create complexity, depth and balance. My view is as an industry we don’t talk enough about mouthfeel and texture in whisky.

The Rationale Behind 46.4% ABV

Our refusal to chill filter then dictates our bottling strength. Ethanol is a natural solvent. If a non-chill filtered whisky were to be watered down to the legal minimum for Scotch Whisky of 40% ABV, there would no longer be enough alcohol to keep the heavy flavour oils dissolved and the liquid will turn cloudy.

The chemical tipping point that prevents this is 46% ABV. At this strength and above, the alcohol concentration is high enough to keep the lipid chains dissolved and in suspended at room temperature.

This is the reason we always bottle our single malt at 46.4% ABV (or higher for our other releases). It is the perfect equilibrium, allowing us to gently reduce our spirit with our RO well water, while maintaining the structural integrity of the oils and esters. It naturally prevents a permanent haze and requires no mechanical chill filtration.

Bottling on the Island.

Once married and reduced, we are ready to bottle our single malt. As with our maturation and vatting, 100% of our bottling takes place on Raasay.

In order to bottle our different releases, we have two separate bottling lines. For our single cask releases, we use our manual 4-head vacuum filler. This a very manual process which you can see in the video at the beginning of this post.

For our other releases, including The Draam, we using our automated bottling line which runs at between 1000 to 2000 bottles per hour.

The Automated Bottling Sequence

Even on the automated line, the process begins and ends with the human touch.

Infeed & Bottle Cleaning: We manually load our bespoke, textured rectangular bottles onto the infeed conveyor belt. Each bottle then moves along the conveyor to be air cleaned to ensure the removal any dust or other particles.

Filling and Corking: The bottles move through to the automated vacuum filler. Vacuum filling is a precise technique, the machine draws the air out of the bottle, creating a negative pressure that gently pulls the liquid in filling exactly 70cl of our single malt. This is then followed immediately by the mechanical insertion of our branded wooden top cork.

Labelling & the “Saloon Doors”: Labelling our heavily textured, rectangular bottle presents a unique mechanical challenge compared to a standard cylindrical glass bottle. As the bottle exits the bottling machine, the label and the cork strip are applied. To secure these the bottle passes through what we refer to as the “saloon doors.” A set of spring hinged gates designed to apply even, firm pressure across the leading edge and corners of the bottle, eliminating air bubbles and ensuring the label adheres to our bottle.

The Heat Tunnel: Finally, the bottles pass through a high temperature shrink tunnel. This rapid, controlled application of heat shrinks our anti-tamper seals tightly around the neck and cork, ensuring product security and a neat finish.

From Raasay to the World

As the bottles come off the line, our team take over once again. They bottle is hand packed into a gift box, then placed into the outer case which are stacked onto pallets ready for dispatch.

This brings our philosophy full circle, only leaving Raasay once it is sealed in a bottle and ready to be enjoyed. From our maturation warehouses to the bottling line and finally out to the wider UK and 52 international markets, every drop remains entirely under our control on the Hebridean island where it was made.

The Island Experience

From the milling the malted barley, through mashing and fermentation, to distillation in our copper stills and the years of maturation in our unique six cask recipe, every step of our whisky’s journey is shaped by the Hebridean elements of the Isle of Raasay.

As I have hopefully explained in this article, our island centric philosophy continues right through disgorging, carefully marrying the spirit, reducing it with our water, all the way to the final seal on the bottle. We take immense pride and satisfaction that our single malt never leaves Raasay until it is in a finished bottle. Creating an uncompromising spirit of our island, crafted under our control from malted barley to bottle, ready to be poured and enjoyed all around the world.

Whey not come to Raasay? Stay, eat and drink with us, you can Book here

So what is distilling?

For me double copper pot distillation for our Isle of Raasay Hebridean Single Malt Scotch Whisky is about separating compounds using their different boiling temperatures (fractional distillation) and concentrating other chemical compounds that create flavour and mouthfeel (congener concentration).

Wash Still

Made of copper our wash still has a capacity of 5000 litres. This is where the first distillation takes place. The wort is pumped from the washback to the wash still via the heat exchanger that preheats the wash using the heated recovered from the pot ale and spent lees. We have a balanced process on Raasay with a one tonne mash that creates 5000 litres of wort that goes into our 5000 litre washbacks, then into our 5000 litre wash still. Everything is one for one resulting 3 casks filled with new make spirit from each run. Ideal for our traceability (and transparency) as we can trace any three cask back to 1 tonne of barley.

Our wash still has a lantern neck and is relatively short and stout. It contains a steam coil in the bottom and works very much like a kettle. Alcohol boils at a lower temperature (78.37 °C) than water (100 °C). This means as we heat up the wash in the wash still the alcohol turns in to vapour before water. So essentially we are separating and concentrating the alcohol. Running the wash still takes about 8 hours and results in a liquid that is about 20% alcohol and is referred to as low wines. This wash still distillation is sometimes referred to as a “stripping run.” It simply separates the alcohol from the dead yeast and water, creating “low wines” at about 20% abv.

The composition of our wash now really comes into it own. If you haven’t ready my previous post it worth reading it now to understand what I mean by the composition of our wash. This is the link; Fermantation of Raasay, alcohol and beyond

The Maillard reaction and The Temperature Paradox in the Wash Still

The Maillard reaction is a form of non-enzymatic browning that occurs between amino acids (from our yeast autolysis and proteins) and reducing sugars.

If you think about cooking a steak, the Maillard reaction requires temperatures between 140°C and 165°C to occur. In addition it requires the presence of amino acids & reducing sugars. This rapidly creates the browning and intense flavour on the surface of the meat.

But in our wash still the bulk of our wash is water and ethanol, meaning the liquid itself boils and turns to vapor between 78.37°C to 100°C hence the temperature paradox.

So, how does the Maillard reaction happen in our wash still?

The reaction does not happen in the bulk of the wash, instead it happens at the boundary layer where the wash meets the surface of our steam coils. The steam is under pressure 2.4 bar which means the surface temperature of the coils is ~138°C.

Time and Acidity.

As I said previously the Maillard reaction requires temperatures between 140°C and 165°C to occur rapidly but this reaction can occur at lower temperatures, even as low 90°C but requires much more time. As we are running our wash still for up to 8 hours this provides the necessary time with a surface temperature of 138°C on the steam coils for the reaction to occur.

Additionally, the lactic acid from the lactobacillus development in the washbacks creating a lower pH in the wash, which alters the reaction pathways favouring the production of specific aromatic compounds.

What are these compounds:

• Furfural: This is the hallmark compound of the Maillard reaction in whisky. It delivers notes of baked bread, almond, toasted grain, and sweet marzipan.

• Pyrazines: Created by the bonding of amino acids and sugars under heat, these compounds carry aromas of roasted nuts, coffee, and toasted cereal. While many pyrazines are too heavy to vaporize completely, lighter pyrazines will carry over into the spirit, giving it a robust “cereal” character.

• Thiazoles: When sulphur containing amino acids (released during yeast autolysis) react with sugars, they create thiazoles. In small, controlled amounts, these add a desirable meaty, savoury flavours and richness to the spirit’s mouthfeel.

Bonus Reactions in the wash still.

Ethyl Lactate: While not a result of the Maillard reaction, this is a direct thermal result of our lactobacillus fermentation. The heat in the wash still forces the lactic acid to esterify with the ethanol, creating ethyl lactate. This compound is responsible for a rich, creamy, buttery mouthfeel.

Diacetyl (2,3-butanedione): Created in trace amounts in our wash by the lactobacillus in particular L. paracasei, it is volatile with a boiling point of ~88°C so distils across easily. Furthermore the yeast and lactobacillus also produce a tasteless, odourless precursor compound called alpha-acetolactate. The heat in the wash still breaks down the residual alpha-acetolactate, converting it into additional diacetyl increasing the overall concentration in our low wines. It helps to give our spirit a slick, oily, and heavy coating on the palate.

In combination Ethyl Lactate and Diacetyl create creamy, buttery textural elements with rich, sweet, butterscotch flavours.

Do we get Caramelisation in our wash still on Raasay?

The short answer is probably not. Caramelisation typically requires much higher temperatures than we achieve in our wash still. Starting around 160°C for standard sugars, and up to 180°C for maltose and maximum we achieve ~138°C. True caramelisation is actually quite rare in a steam heated wash still.

This is the strictly thermal degradation (pyrolysis) of sugars, requiring no amino acids and only truly occurs in a direct-fired still where localised scorching occurs on the copper base.

So when we identify a “caramel” flavour in our new make spirit this is typically a by product of the Maillard reaction.

The Magic of Copper

Copper is highly chemically reactive and acts as a catalyst. This catalytic reaction removes impurities like dimethyl trisulphide creating copper sulphide. The lower the pH (more acidic) the wash the more efficient the catalytic reaction. Our hot, acidic wash acts as a powerful solvent. As it boils and splashes against the copper, the acid constantly dissolves and washes away that copper sulphide acting like a chemical scourer, continuously exposing fresh, reactive copper to the wash and vapour. Effectively removing more sulphur compounds preventing our spirit having meaty, rubbery, or sulphur notes (like struck matches).

The lower pH, acidity of the wash also helps us to “control” the level thiazole allowing copper to remove it’s sulphur precursors.

Copper doesn’t just remove impurities like sulphur, it is also a catalyst for esterification. Bonding of acids and alcohols to create the dark fruit flavour compounds we are looking for.

Esterification is an acid-catalysed reaction. By bringing a low pH wash into our wash still, we are essentially providing a surplus of free hydrogen ions (protons). When these hydrogen ions meet the hot copper surface, the rate at which organic acids like lactic acid bind with ethanol to create esters like ethyl lactate, increases dramatically.

What are the chemical compound that create the dark fruit flavours we are looking for?

• Ethyl Hexanoate (Ethyl Caproate): This is a 6-carbon ester that brings big notes of red apple, sweet anise, and blackberry.

• Ethyl Octanoate: This is a 8-carbon ester that due to our cut points in our spirit still we only get in trace amounts. It brings lighter stone fruits flavours think apricots and peaches.

Wash Still Lyne Arm

The lyne arm is the copper pipe connecting the still to the condenser. At our Isle of Raasay distillery, the lyne arm on our wash still is slightly descending and features a cooling jacket on its first section. This is highly unusual and I think the only one of its kind in Scotland.

After the cooling jacket, there is a collection pot with a stainless steel return pipe leading back into the pot of the wash still, controlled by a hand valve. The cooling jacket is always on, sharing the cooling duty with the main wash still condenser.

When the return hand valve is open, we create an active reflux loop. The cooling jacket condenses the heavier vapours early in their journey, sending them back into the boiling wash, while the lighter, highly volatile vapours (like our fruity esters and diacetyl) easily make it across to the condenser.

This loop intentionally concentrates the heavy compounds inside the wash still, forcing them to interact with the hot surface of the internal steam coils for a longer period. As the run progresses and we distil down to water, this concentration of heavy compounds finally distil across at the end of the run.

Because this liquid is continually returning back into the still, the increased copper contact removes more sulphur impurities, resulting in much cleaner low wines. However, because we have concentrated the heavy compounds such as Ethyl Lactate, long chain fusel oils, and heavy Maillard reaction products the resulting low wines are oily and viscous, with greater mouthfeel.

Conversely, when the hand valve is closed, everything distils across conventionally, resulting in a lighter, less oily batch of low wines. This gives us two distinct flavour profiles of low wines. We typically run with the valve open to build a heavy, viscous base when using our heavily peated malt barley (48 to 52 ppm), and keep it closed for a cleaner, lighter profile when running unpeated malt barley.

Wash Still Condenser

After the lyne arm, the vapours enters our copper shell and tube condenser. While the fundamental goal here is simply to cool the hot alcohol vapours back into a collectible liquid, the equipment we use to do it plays a massive role in our final flavour profile.

We have purposely chosen to use a shell and tube design rather than the traditional Scottish worm tub method (which relies on a single, slowly tapering coiled pipe submerged in a large vat of water). Inside our condenser, the hot vapor enters the copper shell and is forced across a dense network of small, tightly packed copper tubes running with cold water.

This design is vastly more effective and thermodynamically efficient for two reasons. First, it exponentially increases the copper surface area. This provides an pass of catalytic sulphur-scrubbing while the alcohol is in its vapor phase, ensuring our low wines are remarkably clean. Second, it causes the vapour to rapidly “crash” back into a liquid state. This rapid phase locks in the highly volatile, delicate fruity esters we worked so hard to create in the still and during fermentation, holding them safely in the liquid low wines before they can be lost to the atmosphere.

The Sub-Cooler

After the main condenser, the liquid passes through a stainless steel heat exchanger that acts as a sub-cooler. Our primary condenser cooling water is supplied via a closed loop cooling tower, which relies on evaporative cooling. However, when the outside wet bulb temperature rises above 18°C (and yes, does happen on Raasay) the cooling tower loses its efficiency and cannot reduce the return water temperature low enough to fully chill the low wines.

In these warmer outdoor conditions, the sub-cooler is essential to ensure the low wines are cooled below 20°C. This temperature threshold is critical for volatility retention. If the low wines are allowed to enter the receiver warm than this, it would allow the lightest, most delicate ester compounds to evaporate and escape through the tank vents, changing the flavour profile of our low wines. By having and using the sub-coolers we ensure we don’t lose those bright, volatile top notes we have worked to hard to produce.

Low Wines Receiver

This is the stainless steel tank where the sub cooled liquid is collected and held. The resulting low wines sit at about 18% to 20% ABV. This a slightly lower alcohol concentration than may be normal and that is the direct result of running the wash still slow enough to capture those heavy, late-running dark fruit esters and oils. Because stainless steel is chemically inert, this tank acts as a homogenization point. It safely preserves the exact chemical profile we just built, recombining the sweet esters, trace diacetyl, and heavy Maillard compounds (Furfural & Pyrazines) into a single, unified liquid ready for the spirit still.

Pot Ale

This is the by product left behind in the wash still. Having successfully stripped away the alcohol and volatile flavour compounds, what remains is a dense, highly acidic liquid (due to the lactic acid from our long fermentation). It contains the “cooked” dead yeast cells from autolysis, the residual non-fermentable dextrins, and the heavy Maillard reaction by products that were too large to vaporize. Crucially, it also contains the bound precipitated copper sulphide, the physical evidence of our copper still successfully removing the impurities and sulphur notes from our spirit. Normally because this pot ale is so rich in proteins and minerals, it is repurposed as animal feed or fertiliser. Give our location this is not an option so we keep the pot ale in a holding tank and recover the heat to preheat the next wash.

The Spirit Still

Made of copper, our spirit still has a capacity of 3600 litres and is where the second distillation takes place. The charge for this still is a mixture of the sub-cooled low wines pumped from the receiver, combined with the feints (the recycled heads and tails) from the previous spirit distillation. This liquid is a concentration of everything we have created so far. The unfermentable dextrins from our mash, the lactic acid and diacetyl from our 3-to-5-day fermentation, and the heavy Maillard reaction compounds generated by the wash still’s steam coils.

Our spirit still has a traditional swan neck but is relatively short and stout. This specific shape is critical to our Isle of Raasay distillery new make.. A shorter neck means heavier chemical compounds do not have to travel as far against gravity to carry over, which actively promotes a heavier, more viscous, and oil-rich spirit.

The still contains an internal steam coil at the bottom and works very much like a kettle as I mentioned when discussing our wash still. As alcohol boils at a lower temperature (78.37 °C) than water (100 °C), as we apply heat, the alcohol and volatile flavour compounds turn into vapour before the bulk of the water. Running the spirit still takes about 6 to 8 hours.

Making the Cuts

As is traditional in Scotch Whisky, we only collect the “heart” of the run, separating it into three distinct parts:

1. The Heads (Foreshots): Highly volatile and undesirable compounds, like methanol and solvent-like esters, vaporize first. We divert these away from our final spirit and send them to the intermediate spirits receiver.

2. The Hearts: Once the alcohol concentration drops to about 72% ABV, the distiller noses the run and makes the cut to the spirit receiver. The early hearts are packed with bright, sweet orchard fruit notes (Ethyl Hexanoate) and trace diacetyl, which immediately starts building a slick, buttery texture on the palate.

3. The Tails (Feints): The run finishes with the heavy, bitter compounds. These are diverted back to the intermediate spirits receiver to be redistilled in the next batch.

The Crucial Cut Point.

We take a fairly narrow cut either from 75% abv down to 67% or 65% ABV We switch from collecting spirit at these two different points depending on the malt we are running. For our unpeated spirit, we cut at 67% ABV, yielding a cleaner, lighter, and more floral profile.

However, we are using our heavily peated malted barley (48 to 52 ppm), we run down to 65% ABV. Why?

By dropping to 65%, we capture the beginning of the very heavy, late-running, long-chain esters (like Ethyl Octanoate and Ethyl Decanoate). These are the specific compounds responsible for the rich, dark fruit flavours of plum, fig, and blackberry. Furthermore, cutting at 65% allows the heavier fusel oils, ethyl lactate, and savoury thiazoles to start to cross over. All of this results in a peated spirit with more structural weight, oily mouthfeel, and a complexity balancing sweet and savoury.

Click the image above to open the interactive Distillation Cut Visualizer and explore the chemistry for yourself!

The Spirit still Lyne Arm.

The copper pipe connecting the still to the condenser is referred to as the lyne arm. Interestingly, the lyne arm on our spirit still is slightly ascending. As the vapours travel slightly uphill, the absolute heaviest and more bitter fusel oils cool, condense, and run back down the neck into the still. This process, known as natural reflux, acts as a cleaning mechanism removing impurities and less desirable flavours. While our short, stout still drives a heavy, oily, dark-fruit spirit upward, the ascending lyne arm helps to ensure it never from becoming overly heavy or soapy, creating a balanced yet robust new make.

Share

The Six-Plate Bubble Cap Purifier:

Our Virtual Third Still

While our ascending lyne arm provides natural reflux, we have a highly specified piece of engineering sitting (in the corner and) just before the spirit condenser. It is a six-plate copper bubble cap purifier column, topped with a dephlegmator (a partial condenser).

This purifier can be either on or off using a set of directional valves at the end of the lyne arm. When the main valve is closed and the purifier valve is open, all the vapour from the spirit still is redirected into the bottom of this column. The dephlegmator at the top cools a portion of the rising vapour, condensing the spirit vapours which drop back down forming a liquid layer on each of the six copper bubble cap plates. As the hot vapours rise, they bubble through this cool liquid layer, condensing and re-boiling on each plate.

This active reflux strips water out of the vapour at a very high rate, increasing the final collection from our typical 70% ABV up to a higher 80% to 85% ABV in a single pass. It effectively acts as a virtual third still, turning our traditional swan neck into something akin to Carterhead or Lomond still. Or to quote Dave Broom “a deconstructed Carterhead still”.

What is the impact on flavour? The Blackcurrant Focus.

When we run the spirit still conventionally, our goal is to carry over the heavy oils, trace diacetyl, and savoury thiazoles created by our 3-to-5-day fermentation, resulting in a thick, oily, roasted-fruit spirit.

However, when we engage the purifier, the chemical profile changes entirely. The increase in reflux in the mini column physically prevents those heavy, oily fusels and savoury compounds from reaching the top, returning (via a separate stainless steall return pipe) back into the pot of the spirit still. What makes it through to the condenser is purified, concentration of our lighter and medium-chain esters.

Without the heavy, oily compounds masking the palate, the sweet berry esters (Ethyl Hexanoate) and trace tart sulphur compounds (thiols) from our long fermentation are spotlighted. The result is a very different new make spirit; cleaner, lighter in texture, and focused notes of dark fruit and intense blackcurrant.

By simply turning a valve, this chemical engineering allows us to capture the exact same fermentation biochemistry in two entirely different ways. One heavy, oily, and savoury; the other bright, clean, and full of intense dark berries.

If you are interested in tasting the results using our virtual third still there is currently a single cask, cask strength bottling available that allows you to do just that.

Raasay 3.4 times distilled

Spirit Condenser & Sub-Cooler

Following the lyne arm (or the purifier column, if engaged), the vapour enters our copper shell-and-tube spirit condenser. Just as it does on the wash still, this design provides an efficient final pass of copper contact to ensure level of purity we are looking for.

After the condenser, the liquid passes through our stainless steel heat exchanger (sub-cooler). As mentioned earlier, this ensures the new make spirit is chilled to keep it consistently below 20°C, regardless of how warm the outside wet bulb temperature makes our cooling tower water (yes, even on an Inner Hebridean island of the North West coast of Scotland).

Why is this critical? If the new make spirit were allowed to run above 20°C, the highly volatile, delicate ester top-notes, the bright fruit aromas that balance our heavy, oily baseline, would evaporate into the still house air before we could collect them.

The Spirit Safe

The chilled spirit flows directly into the spirit safe. Historically, HMRC required the traditional brass and glass cabinet to be securely padlocked so no untaxed alcohol could go missing. Today, this is not the case, acting as the distiller’s control centre. It also always us to be able to use our rather beautiful Italian copper spirit safes, one for the low wines and a separate one for our spirit.

Inside the safe, we use a hydrometer and a thermometer (for temperature correction) to monitor the dropping ABV of the run. While these instruments tell us when we are approaching our 67% (unpeated) or 65% (peated) cut points, the safe also allows the distiller to continuously nose the spirit and use their experience to inform when to take the cut. The arithmetic tells us the ABV, but it is the distiller’s sensory evaluation that confirms the exact balance of dark fruit esters and heavy oils has been perfectly captured before making the cut.

Spirit Receiver and Dilution

Once the cut is made, the “heart” of the run flows into our stainless steel spirit receiver. It is held here before being pumped to the warehouse, breaking that golden rule when designing a distillery of “always use gravity wherever you can”. Once in the SRWV in the warehouse it is reduced to our cask filling strength of 63.5% ABV using water drawn directly from our own well on site.

This dilution step is where the physical mouthfeel of our spirit is becomes locked in. As we cut our spirit run down to 65% ABV to capture long-chain esters and heavy, viscous fusel oils, our new make contains a lot of lipids and fatty acids. When we introduce our well water to reduce the ABV to 63.5%, the solubility of the liquid changes. Water and heavy oils naturally repel each other, they really do not want to mix. This reaction forces those heavy flavour compounds to “clump” together into microscopic suspensions (known as micelles). It is this chemical interaction results in our spirit coating the palate, giving our Isle of Raasay spirit its thick, lingering, and oily mouthfeel.

Share

If you’ve got this far thank you for reading and if you enjoyed what you read please share this post.

It feels like that was quite an intense summary of our distilling process on Raasay but I hope that helps bring together and make sense of all my other post so far. As to my next post, well I think a may step back for a wee while and reflect on what may come next.

Having previously covered oak species, our oak policy, maturation, barley varieties, milling and mashing, I now want to discuss our fermentation at Raasay Distillery.

See my previous posts

Share

It is obvious but worth making the point, if you don’t create the flavour and mouthfeel you are looking for during fermentation, then these compounds will not be there to distil across into your new make spirit. Fermentation is the vital foundation of our whisky’s character. When designing the distillery I wanted to have a number of things that could be off or on that would allow us to to create different new make spirits.

The Washbacks

Our fermentation takes place in six stainless steel vessels known as washbacks, each with a capacity of 5,000 litres. Each has a cooling jacket that can be off or on. More on this later when I talk about fermentation temperatures.

The washbacks are the destination for the sweet, cooled, clear wort fresh from the mash tun. The process of inoculating the wort with yeast, known as pitching, is a carefully timed operation. We add the yeast just after the first water enters the washback. As the second water flows through from the mash tun, it acts as a natural agitator, perfectly mixing the yeast into the liquid to kickstart the process.

Our Yeast

Yeast (Saccharomyces cerevisiae) is a single celled fungus responsible for fermentation. We use freeze-dried yeast which we rehydrated to wake it up before being introduced to the washback. To achieve the distinctive Isle of Raasay flavour profile, we use the following yeast.

Two different distillers yeast, DistilaMax® MW from Lallemand and Hercules Yeast from WHC Lab (a Saccharomyces cerevisiae var. diastaticus strain). Both produce the dark fruit flavours during fermentation that we are looking for.

A Champagne yeast, DistilaMax® LS from Lallemand (a selected strain of Saccharomyces cerevisiae bayanus). This also helps us create the dark fruit flavours that we are looking for but brings drier, biscuity almost effervescent notes.

It is worth noting that Champagne yeasts naturally ferment fruit, grapes where their primary food source is fruit juice. Fruit sugars are almost entirely simple monosaccharides, specifically fructose and glucose. Where distillers' yeasts are naturally ferment grain, malted barley. Our malt wort is typically composed of 50 to 60% maltose (a two-part complex sugar), 15-20% maltotriose (a three-part complex sugar), and only about 10-15% simple glucose and fructose.

As a result when we use LS yeast to ferment our malt wort the alcohol yield lower as it is looking for fructose and we are providing mainly maltose. Again for us it is all about flavour development. In November this year (2026) we are planning a release of our single malt fermented with a 100% champagne yeast and we have previous released a single cask bottling fermented with 100% LS yeast. An opportunity to taste the resulting drier, biscuity almost effervescent notes.

Another yeast from WHC that we have used is their Pineapple Passion yeast. Pineapple Passion is a specialized Saccharomyces cerevisiae strain developed primarily for the craft beer world, specifically for brewing hazy, juicy, tropical New England IPAs (NEIPAs).

It’s key characteristics are vibrant ester production. As the name suggests, this strain is specifically selected for its ability to create tropical, fruity esters during fermentation. It produces compounds like ethyl butyrate, which is perceived on the palate and nose as distinct, fresh pineapple.

High Biotransformation, in a distilling context, this highly active enzymatic behaviour interacts with the complex compounds in malted barley to create entirely new, exotic flavour precursors in the wash.

In brewing Pineapple Passion is celebrated for its “haze stability.” It leaves behind complex proteins and unfermented elements that create a thick, juicy, and rich mouthfeel. When run through our pot stills, the resulting heavy, protein-rich wash translates to a very viscous, oily spirit.

Pineapple Passion is not a diastaticus yeast, it does not break down complex malt dextrins on its own, as a result it leaves more residual sweetness and body in the wash, resulting in a slightly lower overall alcohol yield than our distillers’ strain. However we are currently maturing our spirit produced using this Pineapple Passion yeast in ex Matugga Rum casks. It really is going to be a tropical, pineapple delight of a single malt, a very special release at some point in the future.

We have also used spent brewers yeast. Historically, it was common practice for distilleries to buy leftover (or “spent”) yeast from local beer breweries. Originally done simply to save money, many new wave distillers appreciate that pitching this exhausted yeast alongside standard distillers’ yeast dramatically altered the character of the resulting wash. Brewer’s yeast is fundamentally different from distillers’ yeast. It typically has a lower alcohol tolerance and is not genetically optimized to rapidly break down complex sugars (maltose and maltotriose) found in our higher gravity wort.

When spent brewer’s yeast, which is already exhausted from fermenting a batch of beer, is pitched into our washback, it faces a highly stressful environment. Because it cannot survive the rising alcohol levels as well as our distillers’ strains, it dies off much earlier in the fermentation process. This early death triggers rapid autolysis (the rupturing of the yeast cell walls) which I will discuss later on in this article.

We have combined the addition of spent brewers yeast alongside our distillers yeast with much longer fermentation time, up to three weeks. Maturing in a number of different cask types, the resulting new make spirit has been ear marked for some very special future releases.

The Yeast Lifecycle, Lag Phase and Exponential Growth

Once the yeast is introduced to the nutrient-rich wort, it doesn’t instantly start producing alcohol. Instead, it enters what is known as the lag phase. During this initial period, the yeast cells are acclimatising to their new environment. They absorb oxygen, minerals, and amino acids from the wort, preparing for the hard work ahead.

Following this brief adjustment period, the yeast enters the log phase (or exponential phase). This is a period of explosive, rapid growth. Yeast cells multiply asexually through a process called budding. A small protrusion, or “bud,” forms on the parent cell, growing larger as the parent replicates its DNA and shares it with the newly forming daughter cell. Eventually, the bud pinches off to become an independent yeast cell, ready to consume sugars and begin budding itself. This exponential multiplication is what turns our initial pitch of yeast into the vigorously activity we see over the next 24 to 48 hours.

Fermentation & Temperature Control

During this vigorous metabolic process, the yeast converts the sugars in the wort into alcohol (ethanol), carbon dioxide (CO2) and creates heat.

At a chemical level, the primary fermentation reaction is expressed as:

C6H12O6 (glucose) —> 2C2H5OH (ethanol) + 2CO2(Carbon dioxide) + 2ATP (energy)

Alongside alcohol and CO2, this reaction creates a wide array of complex flavour compounds (congeners) such as fruity esters and floral aldehydes but as already mentioned it also generates a significant amount of heat.

Temperature during fermentation is a critical, specifically concerning the creation of higher alcohols (also called fusel oils). These are heavier alcohol compounds, such as propanol and amyl alcohol, produced as part of the yeast’s amino acid metabolism.

The concentration of these compounds in the wash is dependent on temperature. At lower fermentation temperatures (below 30°C), the yeast’s metabolism is slower, producing fewer of these fusel oils and resulting in a lighter, cleaner wash. At temperatures above 30°C, the yeast’s metabolic pathways change increasing the production of fusel oils. By utilising the cooling jackets on our washbacks we control or rather stop the fermentation at the desired maximum temperature in turn define the final spirit weight, complexity, and mouthfeel.

In general we have the cooling jackets on when we are fermenting unpeated malted barley and off when we are fermenting peated malted barley. This helps us create heavier, more complex, viscous peated spirt and a lighter, less viscous unpeated spirit.

The Luxury of Time, 3 to 5-Day Fermentations

In the fast paced, high volume, efficient world of modern whisky production, the industry standard for fermentation typically ranges from 52 to 62 hours just enough time to maximize the alcohol yield before refilling the washback.

At the Isle of Raasay Distillery, as with other small, independent, new wave distilleries we prefer a longer fermentation. We ferment for 3 and 5 days (72 to 120 hours). We deliberately prioritize flavour development and mouthfeel over just alcohol production. The 3 day fermentation produce a different flavour profile from our 5 day fermentation, intentional creating more complexity and depth in our single malt.

Autolysis, Creating Texture and Depth

During the first 48 hours, the yeast works hard consuming the sugars, generating almost all of the alcohol. By the 72 hour (3 day) mark, all of the sugars have been used up and the environment has become increasingly alcoholic, at the point the yeast cells reach the end of their lifecycle and start to die off.

As these yeast cells die, their cell walls split open in a process called autolysis (or lysis). This rupturing of the yeast cells releases a wealth of intracellular contents such as amino acids, lipids, and enzymes into the wash. Not only does this create richer, savoury flavour compounds, but it also gives our wash a distinctively creamy, oily textural mouthfeel that translates beautifully into our final spirit. I don’t think mouthfeel is considered or discussed enough. It’s a crucial component of Scotch Whisky.

Some key benefits of Autolysis:

• Nutrient Release: When the yeast cells burst open amino acids, lipids, vitamins, and enzymes are added directly into the wash.

• Supercharging Lactic Bacteria: The nutrients released yeast act as the ultimate superfood for Lactobacillus. This causes a rapid surge in bacterial activity.

The beauty of Lactic Fermentation

So if all of the yeast cells have died off why do we continue fermentation past 72 hours? It is because we move into a crucial secondary phase: lactic fermentation. As the yeast activity subsides, Lactobacillus which are beneficial (friendly) bacteria that naturally occurs on the husks of our malted barley start to multiply.

These bacteria feast on the dead yeast cells and remaining nutrients, producing lactic acid introducing a whole new layer of complex flavours. The lactic acid produced lowers the pH (acidity) of our wash. The lower the pH of the wash the greater the catalytic reaction with the copper in the Wash Still. This catalytic reaction removes impurities for example sulphur during the wash distillation helping to create “cleaner” low wines. The lactic acid also reacts with the esters already produced by the yeast creating longer chain esters. These longer chain esters create the rich dark fruit flavours we are looking for that distil across into our new make spirit.

To full understand our Raasay microflora we sent our wash off for analysis, Nanopore Metagenomics research to be precise.

Nine different lactic acid bacteria (LAB) species were identified within the bacterial communities in our wash including Lacticaseibacillus paracasei, Lacticaseibacillus rhamnosus, Lacticaseibacillus casei, Limosilactobacillus fermentum, Schleiferilactobacillus harbinensis, Lactobacillus delbrueckii, Lactiplantibacillus plantarum, Leuconostoc lactis, and Lentilactobacillus parabuchneri.

Among these, L. paracasei, L. fermentum, and S. harbinensis were the predominant species. There was a substantial increase in the relative abundance of S. harbinensis on the fifth day led to a significant population reduction of L. delbruecki, L. plantarum, and L. lactis.

What does that all mean?

This analysis proves this bacterial phase is vital for our spirit’s character. Not only does L. paracasei (which is the most dominant of these bacterial species) secrete complex carbohydrates that physically thicken the wash, giving it a heavy, oily mouthfeel but it also fundamentally changes the wash’s chemistry. When this lactic acid interacts with the alcohol under the intense heat of our copper pot stills, it undergoes a chemical reaction to create ethyl lactate. This highly desirable ester is responsible for the sweet, creamy, buttery, and soft fruit notes that define the Isle of Raasay’s final new make spirit.

Lastly for any microbiologists reading, it’s worth noting that L. parabuchneri, constituting less than 1% of bacterial abundance, exhibited stability between the three and five-day fermentations. This is important as it can form unwanted gas and off-flavours.

It also goes to show you do not need wooden washback to create this beneficial (or otherwise) microflora.

Ready for the Stills

Once this 3 to 5 day biological dance concludes, we have our wash at about 8% ABV (alcohol by volume). This “distiller’s beer” is finally ready with all it’s mouthfeel, complexity and depth to be transferred to the wash still.

And yes, you’ve guessed it, my next article will be discussing our copper pot stills and our distillation process on Raasay.

After my initial two articles which focused on oak species, their geography and how that influences the maturation of our Hebridean single malt, I thought a change of topic was in order. In this article I talk about the beginning of our process and our barley.

Share

We have used several different barley varieties for distilling on Raasay from commercial to heritage and landrace.

Concerto (commercial variety)
Laureate (commercial variety)
Diablo (commercial variety) Sassy (commercial variety)

It’s fair to say that in terms of flavour there is very little difference in the new make spirit between these commercial varieties. They have a very narrow genetic base, they are highly interrelated (for example, Concerto is actually one of the parents of Laureate). They have been bred by the plant breeders to increase the yield (tonnes per hectare) from the field and to increase fermentable extract i.e. the alcohol yield (litres of pure alcohol per tonne) in the distillery. Inadvertently increase the length of the growing season in the process. So worth noting that these commercial varieties will not ripe in areas with shorter growing seasons e.g. Raasay.

For commercial barley varieties plant breeding for approved Scotch Whisky varieties requirements in addition to yield are:

• Non-GN Status (Crucial for Distilling): All modern malting barley bred for Scottish distilling must be “Non-GN” (non-glycosidic nitrile). Glycosidic nitriles are naturally occurring compounds in some barleys that, during the distillation process, can convert into ethyl carbamate (a recognized carcinogen). Plant breeders strictly select for the recessive non-GN gene.

• The Nitrogen vs. Starch Trade-off: Alcohol yield is dictated by the amount of fermentable sugars (starch) in the grain. Breeders specifically select for grains that partition their energy into making starch rather than protein. For distilling, the grain nitrogen content must be very low (ideally under 1.65%).

• Agronomic Resilience: Breeding for “standability.” They select for short, stiff straw to prevent lodging (the crop falling over from wind/rain) and brackling (the stem snapping near the head), which is vital for island and coastal farming.

With all of this in mind, in 2017 while the distillery was being constructed on Raasay we carried out the first of three barley variety trials on Raasay. It can be fairly wet on Raasay which means we only have from May to August to grow, ripen and harvest barley and commercial varieties above would take from March to October. By the end of 2019 we had identified four barley varieties that grew, ripened and were harvested on Raasay. Each of the three years trails produce 3 casks of Raasay single malt after malting and distilling. We have total of 9 casks of Raasay barley single malt, possibly some very rare release at some point in the future!

Bere (ancient landrace, 6 row) Grown on Raasay (2017, 2018 & 2019) & in Berwickshire.
Iskria (Icelandic artic variety) Grown on Raasay (2017, 2018 & 2019) Kannas (Norwegian artic variety) Grown on Raasay (2017)
Brage (Norwegian artic variety, 6 row) Grown on Raasay (2018 & 2019)
Sienna (organic variety) Grown organically on Shapinsay, Orkney Islands.
Maris Otter (Heritage variety)

Each of these varieties creates a very different flavour profiles in our Isle of Raasay Hebridean single malt. We have released a single cask bottling of our Berwickshire Bere barley fully matured in an ex Bordeaux red wine barrique. Worth trying to taste the difference the barley variety makes. Raasay Distillery Bere Barley single cask

The definition & explanation of Landrace Barley

Landrace varieties are locally adapted populations of barley that have evolved naturally in a specific region over millennia. Some seed has simply been saved at harvest and replanted by local farmers year after year.

• Genetic Diversity: A field of landrace barley is highly diverse, no two plants are exactly alike. Very relevant in todays changing climate.

• Adaptation: They are deeply tied to their specific environment (terroir), having naturally adapted to survive local weather patterns, poor soils, and regional pests.

• Agronomics: They are essentially evolved “wild” varieties, they are low yielding and highly prone to lodging (falling over) before harvest.

• An excellent example is Bere barley, one of the oldest cereals grown in Scotland. It began life 10,000 years ago in the fertile crescent in the Middle East. Slowly moving with people as they migrated across Europe adapting to each new environment through natural selection. It arrived in the Hebrides about 2,500 years ago. There are different Bere varieties from and adapted to Orkney, North Uist & South Uist.

The definition & explanation of Heritage (or Heirloom) Barley

Heritage varieties are older, intentionally bred strains that were once the commercial standard but have since been superseded by modern, high-yielding commercial varieties like Laureate or Diablo.

• Genetic Uniformity: Unlike the wild diversity of landraces, heritage barleys have a distinct, stable pedigree created by early plant breeders.

• Distilling Value: Revived today by craft distiller these older grains offer distinct, richer flavour profiles and a sense of historical romance.

• Agronomics: lower alcohol yields and less disease resistance compared to commercial varieties, making them more expensive and difficult to grow.

• Classic examples: Golden Promise, Plumage Archer, and Maris Otter.

In summary:

• Landraces are shaped by nature and local geography over thousands of years (highly diverse, unbred).

• Heritage varieties were purposefully bred by humans decades ago left behind by modern commercial agriculture (uniform, but outdated for mass yield).

Direct farms (farmers that grower barley directly for us)
West Backs Farm, Campbeltown (Dugald Graham & sons)
Dhurrie Farm (R&B owned farm) Campbeltowm
Balfour Mains, Shapinsay, Orkney Islands (organic grower)
Paxton South Mains (Alex Home Robertson), [Bere barley], Berwickshire, Scottish Borders.

Malting The Barley.

1. Harvest, Drying, and Dormancy

After harvest, raw barley typically contains 15–20% moisture. If stored at this moisture level, the grain will spoil due to microbial growth.

• Drying: The barley is gently dried using air temperatures below 40°C (104°F) to bring the moisture content down to < 12%. It is critical not to exceed this temperature, as excessive heat will denature the proteins and kill the living embryo, rendering the grain useless for malting.

• Storage & Dormancy: At this stage, the barley is naturally dormant—a survival mechanism to prevent premature sprouting in the field. The barley undergoes an “after-ripening” period in storage silos, usually lasting 4 to 8 weeks (sometimes longer), allowing the hormonal inhibitors naturally present in the grain to break down.

2. Steeping

Once dormancy is broken, the barley is ready to germinate. This is initiated in steep tanks where the grain is submerged in water.

• Time & Temperature: Steeping usually takes 36 to 48 hours with water temperatures carefully controlled between 14°C and 18°C (57°F–64°F).

• The Process: Steeping is not a continuous soak. It utilizes alternating cycles of “wet stands” (submersion in water) and “dry stands” (water drained, air drawn through the grain bed). This provides the embryo with essential oxygen for respiration and removes toxic CO2​ buildup.

• Technical Goal: The objective is to raise the moisture content of the grain from ~12% to a highly precise target of 43–46%. This hydration level is the trigger that signals the embryo to awaken.

3. Germination and Modification

During germination, rootlets (chits) start to form at the base of the kernel, and a shoot (the acrospire) develops under the husk. The barley is transferred to germination beds where it is continuously turned to prevent the roots from matting and to dissipate the heat generated by the grain’s natural respiration.

• Time & Temperature: Germination takes 4 to 6 days in highly humid air (nearly 100% relative humidity), maintained at 15°C to 20°C (59°F–68°F).

• The Chemistry: As the embryo hydrates, it synthesizes gibberellic acid (GA), a plant hormone. This hormone migrates to the aleurone layer (a layer of cells just inside the bran). The GA signals the aleurone layer to synthesize and release an arsenal of hydrolytic enzymes into the starchy endosperm:

  • β-glucanases and Cytases: These break down the tough cell walls surrounding the starch granules.

  • Proteases: These break down the protein matrix holding the starch granules together, creating free amino nitrogen (FAN) which yeast will later need for healthy fermentation.

  • Amylases (α and β): α-amylase is synthesized from scratch, while β-amylase (which is already present in the raw grain but bound to proteins) is freed and activated.

• Starch Structure: It is these amylase enzymes that we require for brewing “mashing.” They are responsible for breaking down the complex starch chains (amylose and amylopectin) into simple, fermentable sugars like maltose and maltotriose. Note: Very little starch is actually converted to sugar during germination; the goal here is simply to build up the enzyme reserves and soften (modify) the endosperm.

4. Kilning (Drying)

If the roots and acrospire continue to develop, the growing plant will consume all of the starch and resulting sugars for its own energy. It is crucial to stop germination at the exact moment the enzyme potential is maximized but before significant starch degradation occurs.

• Free Drying Phase: The germinated “green malt” (at ~45% moisture) is moved to a kiln. High volumes of warm air, around 50°C to 60°C (122°F–140°F), are blown through the bed for 12 to 24 hours. This lowers the moisture to about 10%. Keeping the temperature relatively low while the grain is wet is critical; otherwise, the enzymes we just spent days creating would be permanently destroyed (denatured).

• Curing Phase: Once the moisture drops below 10%, the temperature is ramped up to 80°C–105°C (176°F–221°F) (for standard pale malts) for another 2 to 4 hours. This drives the final moisture down to a stable 4–5%.

• The Chemistry: The elevated curing temperatures trigger the Maillard reaction, a chemical reaction requiring amino acids, reducing sugars and temperatures between 140°C to 165°C. This reaction creates melanoidins, which give the malted barley its final colour (from pale gold to dark brown) and characteristic biscuity, toasted, or roasted flavours.

Once kilned and cooled, the rootlets are knocked off, and the final product is malted barley, stable, flavour-rich, packed with accessible starches, and loaded with the necessary enzymes required to break those starches down into sugar required by the yeast for fermentation.

On Raasay we distil for 6 months with plain malt (unpeated) and 6 month with heavily peated malt (48 to 52 ppm)

Plain malt is malted barley that has been dried using hot air.

Peated malt is malted barley that has been dried using peat smoke. In our using highland peat which produces a fragrant, aromatic wood smoke flavour quite distinct from Islay peat.

Malting Companies (suppliers of malted barley) we have worked with include Bairds, Inverness; Crisp, Alloa, Clackmannanshire (Scotland), Portgordon, Banffshire (Scotland), Great Ryburgh, Norfolk; Boortmalt (Paul’s Malt), Glenesk Maltings, Angus, Buckie Maltings, Morayshire; and Simpsons, Berwick upon Tweed for our Berwichshire Bere barley.

Toll malting

When a direct farm grows barley for us, we buy the barley from them after harvesting and drying. We then have a separate transport, storage and malting agreement with the Malting Company, this is called Toll Malting. It ensure the full provenance and traceability for field to bottle.

Malt Intake

Pneumatic Blower Lorry

Function: Delivery and Intake

• The Process: Malted barley is delivered by a specialised vehicle with a 26 to 28 tonne capacity. Rather than being manually tipped, the malted barley is transferred pneumatically.

• Technical Detail: The lorry uses a high-volume, low-pressure blower system to propel the malt through intake pipework directly into the storage silo. This pneumatic conveying method is carefully calibrated to move the grain efficiently while minimizing friction and impact, preserving the structural integrity of the barley kernel and preventing premature shattering of the husk.

Malt Silo

Function: Bulk Storage

• The Process: A Collinson Silo³ with 30-tonne capacity serves as the primary storage vessel for our malted barley once blown in from the delivery vehicle.

• Technical Detail: The silo is designed with a conical base to ensure “mass flow,” meaning the malted barley feeds out evenly without bridging or leaving stagnant pockets. It protects the malted barley from moisture ingress and pests while managing dust. Because malted barley is highly combustible, the silo and its associated intake systems are designed to strict health and safety standards to mitigate the risk of dust accumulation.

Screw Conveyor (Auger)

Function: Mechanical Grain Transport

• The Process: Encased in what looks like a small white pipe, this Collinson Rotaflex Conveyor system transports the un-milled malted barley from the base of the silo directly into the distillery building to the mill.

• Technical Detail: Inside the pipe is a rotating helical screw, often referred to as “flighting” acting much like an Archimedes’ screw. As the central shaft turns, the flighting physically pushes the malted barley along the enclosed trough. This enclosed design is crucial for dust containment and ensures a consistent, metered feed rate of malted barley into the grist mill hopper, preventing the mill from being choked by too much malted barley at once.

Four-Roller Grist Mill

Function: Milling and “crushing”.

• The Process: Manufactured by Alan Ruddock Engineering, this mill grinds the whole malted barley into a coarse “porridge” known as grist. Operating at a capacity of 0.5 tonnes per hour, a standard one-tonne batch takes two hours to mill.

• Technical Detail: Unlike a simple crusher or hammer mill, a four-roller mill provides controlled, staged milling.

  • Top Rollers: The first pair of rollers is set with a wider gap. Their primary job is to gently pop the barley kernel open and shear the outer husk off as cleanly as possible without shredding it.

  • Bottom Rollers: The partially crushed grain then falls through to a second set of rollers with a narrower, tightly calibrated gap. These rollers crush the exposed starchy center (the endosperm) into the correct consistency.

• Safety: Because milling generates highly combustible grain dust, the mill is ATEX-rated (certified for explosive atmospheres) located in a separate highly ventilated area of our distillery and with an explosion-relief panel in the grist bin.

Grist Composition

Function: Starch Extraction and Mash Filtration

• The Process: The resulting grist is sorted into three distinct components: Grit, Husk, and Flour. At Isle of Raasay distillery our target ratio is 70% grit, 20% husk, and 10% flour.

Why This Ratio Matters:

• Grit (70%): The crushed starchy interior of the malted barley. This is where the fermentable sugars come from. Maximizing this percentage ensures an efficient extraction during mashing.

• Husk (20%): The protective outer shell of the barley. Keeping the husks largely intact is critical, as they act as a natural filter bed inside the mash tun, allowing the sugary liquid (wort) to drain clearly. If the husk is shredded too finely, the filter bed collapses.

• Flour (10%): The finest dust created by the milling process. While it yields high sugar, too much flour will turn to a doughy paste when mixed with hot water, causing a “stuck mash” that prevents the wort from draining. Keeping it at 10% ensures optimal sugar yield without clogging the system.

1-Tonne Semi-Lauter Mash Tun

Function: Enzymatic Conversion and Filtration

• The Vessel: Manufactured by LH Stainless, our mash tun is constructed from high-grade stainless steel. This material is essential not only for strict hygiene but also for superior thermal retention, ensuring temperature stability during the crucial extraction phases.

• Capacity: The vessel processes a single batch consisting of 1 tonne of grist and up to 5,000 litres of hot water (known in the industry as mashing liquor).

The Mashing Process

• Starch to Sugar Conversion: Mashing is not simply mixing; it is a highly controlled biochemical reaction. When the hot mashing liquor meets the grist, it reactivates natural enzymes (primarily alpha- and beta-amylase) developed during the malting process. These enzymes act like microscopic scissors, cutting the complex, insoluble starches locked inside the barley into simple, fermentable sugars.

• Staged Extraction: The 5,000 litres of water are not added all at once. Instead, the liquor is added in stages at progressively higher temperatures (typically three separate “waters”). This staged approach maximizes the extraction of sugars while carefully managing the survival of the enzymes, resulting in a sugary liquid known as wort.

Internal Mechanics: The “Semi-Lauter” Design

• What “Semi-Lauter” Means: “Lauter” comes from a German word meaning to clarify or filter. A semi-lauter tun bridges the gap between a traditional infusion mash tun and a highly mechanized modern lauter tun, offering excellent extraction and clarity.

• Rotating Rakes: Inside the tun is a motorized central shaft fitted with rotating rakes or blades. As the mash rests, these rakes slowly cut through the porridge like mixture. This gentle agitation prevents the heavy grain bed from compacting, ensures an even temperature distribution, and prevents the creation of dry pockets where sugars might be left unextracted.

• The False Bottom: The base of the tun features a specialized “false bottom” made of slotted stainless steel plates.

Filtration and Output

• The Filter Bed: This is where the 20% husk ratio achieved during milling becomes critical. The husks settle on top of the false bottom to form a natural, highly effective filter bed. As the sugary wort is drawn off from the bottom of the tun, it passes through this husk layer, leaving behind a clear liquid ready for fermentation.

• The Byproduct: Once all the sugars have been rinsed (sparged) from the grist, the leftover solid material, now hopefully completely depleted of starch and sugar is called draff. This is a highly nutritious, protein-rich byproduct is collected by the crofters on Raasay to feed their sheep and cattle.

Mashing Dynamics & The Microbiome

Mashing is a delicate balancing act of temperature and chemistry. As the grist and hot water meet, we aren’t just extracting sugars, we are managing a complex microbial environment.

The Lactobacillus Factor:

Malted barley naturally carries a population of Lactobacillus bacteria on its husk. In whisky production, these bacteria can be highly beneficial during fermentation, contributing to the creation of fruity, complex flavour compounds (esters) through the production of lactic acid. However, their numbers must initially be controlled so they don’t outcompete the yeast. The temperature of our first mashing water acts as a thermal barrier at <64.5°C the vast majority of the naturally occurring Lactobacillus don’t survive this temperature. Only a resilient temperature resistant fraction survives the mash to pass into the washbacks, ensuring the bacterial influence later in the fermentation that we are looking for.

The Three-Water Extraction Process

To maximize efficiency while protecting the delicate enzymes, mashing is executed in three distinct, temperature stages.

1. First Water (64.5°C): Enzymatic Conversion.

The first water mixes directly with the incoming grist inside the intake auger, ensuring a uniform hydration that prevents dry clumps (dough balls) from forming. The <64.5°C temperature is critical. It is hot enough to gelatinize the starches so they dissolve, but cool enough that the natural enzymes, developed during malting, do not denature. These enzymes break down the complex starches into the simple, fermentable sugars that our yeast will require. This sugary liquid is drawn off the bottom, cooled to between 18°C and 20°C, and pumped into the washback.

2. Second Water (70°C): Thermal Extraction.

Once the first water is drained, the second water is introduced. Because the enzymes have already completed their crucial conversion work, we no longer need to protect them. Instead, we use a much higher temperature (over 70°C) to dissolve and extract the more stubborn starches and sugars that remain locked in the grain bed. This water is also drawn off and sent to the washbacks.

3. Third Water (80°C): The Sparge.

The final water is introduced via a rotating sparge (spray) bar at the top of the tun. At 80°C, this water acts as a highly efficient, low-viscosity rinse. It washes gently down through the husks, flushing out the very last remnants of extractable sugar.

Resource Management: Hot Liquor Tanks (HLT)

Distilling requires energy and water, so we have recovery of both built into our system. We have two separate Hot Liquor Tanks to manage our mashing water:

• The “Clean” HLT: This holds fresh, pure, heated water used for the second and third mashing stages.

• The “Dirty” HLT (Weak Wort): The sugary liquid collected from the third water (the sparge) isn’t concentrated enough to ferment on its own, but it is too valuable to waste. We hold this weak wort in the “dirty” HLT, preserving both its thermal energy and its residual sugars, and use it as the first water for the next batch of mashing.

The Output: Wort Clarity & Spirit Character

The product of the mashing process is wort, a dark brown, sugary liquid. Distilleries can choose to produce a cloudy or a clear wort, and this choice fundamentally dictates the final character of the whisky.

• The Raasay Style: We specifically designed our process to produce a highly clarified, clean wort. By contrast a cloudy wort carry more grain particles and lipids, which tend to produce a heavier, nutty, or cereal-forward spirit. Whereas our exceptionally clear wort intentionally lacks those lipids. This deliberate lack of lipids slightly stresses the yeast during fermentation, prompting it to produce the specific, complex esters responsible for the elegant spirit and the signature dark fruit flavours that define the Isle of Raasay’s new make spirit.

Thermodynamics: Heat Exchangers

To manage the massive temperature shifts between mashing, fermentation, and distillation, we utilize two highly efficient Plate Heat Exchangers (PHE). These systems pass hot and cold liquids past each other through a series of ultra-thin, corrugated stainless steel plates, allowing them to swap temperatures without ever physically mixing.

1. Wort Cooler: Rapidly drops the boiling-hot wort down to the precise 18-20°C pitching temperature required by the yeast. Simultaneously, this process heats the incoming cold water, recovering energy for the next mash.

2. Wash Pre-Heater: Before the fermented liquid (wash) enters the Wash Still, it passes through this exchanger. Here, it absorbs residual heat from the boiling-hot waste streams (pot ale and spent lees) leaving the stills. Pre-heating the wash significantly reduces the amount of steam and therefore fuel required to bring the still up to boiling point.

Share

In my next article I’ll move onto fermentation. For us on Raasay fermentation is not just about producing alcohol it’s about creating mouthfeel and flavour.

• that has been matured only in oak casks of a capacity not exceeding 700 litres

• that has been matured only in Scotland

• that has been matured for a period of not less than three years

Traditionally only three oak species have been used in Scotland for maturing whisky and in most cases the oak species is not named. You will read North American oak or European oak used for maturation but in most cases just ex bourbon or ex sherry casks.

Yet there are over 600 different species of oak trees in the world (500 in the Northern hemisphere),

To date at our Isle of Raasay distillery we have used five different oak species to mature our Hebridean Single Malt Scotch whisky on the island. They are:

Quercus alba - North American white oak
Quercus muehlenbergii (Chinkapin) – North American white oak
Quercus petraea – European oak
Quercus robur – European oak
Quercus humboldtii – Andean / Columbian oak.

American Rye Barrels – Quercus alba

Most common hardwood of North America. Native to eastern and central North America (Minnesota, Ontario, Quebec, and southern Maine to Florida and eastern Texas).

Synonymous with bourbon barrel, Quercus alba brings the classic vanilla and butterscotch flavours associated with all bourbons. Also used in for rye whiskey, it provides a similar flavour profile but Rye Whiskey has a very spicy black pepper note. Using ex Rye Quercus alba barrels brings more complexity and addition flavour to our single malt.

This flavour from the previous contents is an integral of part of our Nia Sia or 6 cask recipe. The craft distillers in the US have definitely made Rye whiskey cool again and no longer “those good old boys drinking whiskey & rye” (American Pie by Don McLean).

Which distilleries ex Rye casks do we? Woodford Reserve Rye barrels (Early Times and Old Watermill Distilling Company Rye Whiskey) and Sagamore Spirits ex Rye whiskey barrels direct from their distillery in Baltimore to name just two.

Chinkapin Oak – Quercus muehlenbergii

A deciduous species of North American white oak it is native to eastern and central North America in all the same areas as Quercus alba. It is named after Gotthilf Heinrich Ernst Muhlenberg (1753–1815) a prominent American clergyman, educator, and pioneering botanist. He is often considered the first botanist born in America to systematically research the flora and fauna of the USA.

Recognisable by it’s notably different leaf shape compared to Quercus alba. It also brings a completely different flavour profile to our maturing spirit. More mellow yet rich complex flavours, dark fruits rather than vanilla. With our peated spirit it brings BBQ glaze or as Dave Broom described it as “like being in an American diner eating pancakes with maple syrup and smoky bacon bits”.

These barrels are made to our specification in cooperages in the US. Our specification:

• 36 months air drying (seasoning)

• High toast

• High Char

The longer air drying helps to breakdown the lignin in the oak. It’s worth noting that 52% of the dry matter of oak is made up of Lignin. When the lignin breaks down it creates volatile phenols. During maturation of our Isle of Raasay spirit we slowly gain these volatile phenols from the oak adding wood smoke flavours to our Isle of Raasay single malt scotch whisky.

The longer toasting period breaks down and carmalises the natural sugars (Hemicellulose) in the oak creating caramel, toffee, vanilla and butterscotch flavours. This longer toasting period also helps to breakdown the lignin in the oak creating more of the volatile phenols that we are looking for.

The high char creates a charcoal layer inside the barrel. This increases the surface area of the barrel allow the spirit more contact with the oak and to penetrate further into the oak. This gives more colour and increased flavour but equally importantly the charcoal removes impurities from the spirit. All very important when planning to bottle the mature spirit at a younger age.

European Oak – Quercus petraea & Quercus robur

Both species of oak grow widely across Europe including the UK.

Quercus petraea (Sessile Oak) is regarded as having fine or tight grain. It contains high levels of eugenol which gives savoury spices like cloves and cinnamon.

Quercus robur (Pedunculate Oak) regarded as having more open or wider grain giving rich spice and dark fruit flavours (think freeze dried raspberries).

Generally speaking the tighter the grain the longer it takes for the spirit to penetrate the wood and therefore the longer it takes for the fine grain wood to impart its flavour to the spirit. Reversely the wider grain imparts its flavour earlier to the spirit.

Geography and altitude also both have a big impact on how fine or open the grain of the oak is. The further north (in a colder climate) the oak grows the more slowly resulting in a finer grain, the further south (in a warmer climate) the oak grows more quickly resulting in a wider grain. The higher the altitude the colder the growing conditions meaning oak that grows at a higher altitude has a finer grain.

In France the oak is referred to as the forest where it grew. For example Limousin oak from south-central France, predominantly quicker growing Quercus robur and Troncais oak from central France is predominantly slow growing Quercus petraea.

Quercus petraea above on the left can be identified by having a long stalk whereas Quercus robur above on the right the leaf stalk is absent or very short.

At Isle of Raasay distillery we use French oak ex Bordeaux Red Wine barriques (225 litre). All are from Chateaux we work with on the the left bank in Bordeaux. The wines in this area are made predominately from cabernet sauvignon grapes which are high in tannins and take longer to mature in the bottle. These higher tannins is what help develop the dark fruit flavours we are looking for in our spirit

We specify that the casks have been used for three vintages before we take them to Raasay. After 3 vintages the wine has gone as far into the wood as it is going to go. We also specify that the casks are emptied but not cleaned or sterilised using sulphur candles. As sulphur taints the spirit and is an undesirable flavour for our whisky.

We bring the casks to Raasay in the colder months (temp >12*C) to prevent any residual wine oxidising.

Na Sia (the six in Gaelic), our six cask recipe

At Isle of Raasay distillery we refer to our oak policy for The Draam as our six cask recipe or Na Sia. We use three different cask type ex Rye Whiskey barrels (Quercus alba), Chinkapin oak (Quercus muehlenbergii) Barrels and ex Bordeaux red wine barriques (Quercus petraea & Quercus robur). The three cask types incorporate the four oak species discussed above. We produce six months of unpeated spirit and six months heavily peated spirit each year. The two spirit types are fully matured separately in the three different cask types hence our six cask recipe.

After maturation the six cask types are vatted together to create The Draam our Isle of Raasay Hebridean single malt scotch whisky.

Colombian Oak Casks – Quercus humboldtii

This is another oak species that we have used for full term maturation on Raasay. Commonly known as the Andean oak or Colombian oak, Quercus humboldtii only grows in Colombia and Panamá.

Named after Alexander von Humboldt (a German polymath, geographer, naturalist and explorer who travelled extensively in the Americas between 1767 - 1835).

It is an evergreen tree which grows to a height of 25 metres (82 feet) and a diameter of 1 m (3 ft 3 in) and grows at an altitude of 1,000 to 3,200 m (3,300 to 10,500 ft). Found on all three Colombian Andean mountain ranges and some lowland inter-Andean regions.

The timber oak staves are air dried (seasoned) for 24 months allowing them to dry and for the lignin in the wood to start to break down into volatile phenols. These staves are coopered into 225 litre casks / barriques in the cooperage in Columbia. They then receive a high toast and a high charring level. These casks impart distinct caramelized sugar, “crème brûlée” and herbal (think Oolong tea & spearmint) flavours to our Isle of Raasay spirit. These flavours and intense dark colour are noticeable after just three months of maturation but begin to plateau and level out nicely after 24 months. Combined with the lightly peated dark fruit flavours in our new make spirit makes for a very distinctive Hebridean Single Malt Scotch Whisky. What I would describe as a crème brûlée bomb (as opposed to the more traditional sherry bomb whisky). Quercus Humboldtii Virgin Colombian Oak

You can taste all of the oak species mentioned in this article side by side in our oak species maturation pack. Oak Species maturation pack

Common Name | Latin Name

-----------------------------------------+-------------------------------------------

Pedunculate oak | Quercus robur

Late leaf-flushing oak | Quercus robur var. tardiflora

Slavonian oak | Quercus robur ssp. slavonica

Sessile oak | Quercus petraea

Turkey oak | Quercus cerris

Downy oak | Quercus pubescens

Hungarian oak | Quercus frainetto (syn. Quercus conferta)

Red oak (introduced) | Quercus rubra

Pin oak (introduced) | Quercus palustris

Other oak species (minor or hybridized) | Quercus spp.

The species listed in this table represent both native and introduced oaks within Hungary’s forests. The dominant native species are the pedunculate oak (Quercus robur), sessile oak (Quercus petraea), and Turkey oak (Quercus cerris), which form the ecological foundation of Hungarian oak forests.

Interestingly and worth noting, Hungarian oak (Quercus frainetto), although bearing the country’s name, occurs naturally mainly in southeastern Europe and appears only sporadically in Hungary.

Both Quercus robur and Quercus petraea grow widely across the whole of Europe and are the two most predominant oak species in Europe. However, where they grew changes the flavour profile that each of these species create during the maturation of our single malt.

Temperature, rainfall levels and altitude all affect the speed that the oak trees grow at which in turn affects how open or closed the grain of the oak is. This determines how far our spirit will travel into the oak and how much it will affect the flavour. The tighter the grain (slower growing) the less influence, the wider the grain (faster growing) the greater the influence on flavour.

The oak from the Zemplén Mountains (Zempléni-hegység) in northeastern Hungary is one of the world’s most prized woods for coopering. Long before French oak became the undisputed global standard, top winemakers across Europe, including those in France, relied heavily on Hungarian oak to mature their finest wines.

Today, Zemplén oak is experiencing a major renaissance among winemakers and distillers who prize it for its remarkably tight grain, delicate aromatic extraction, and elegant tannin profile. The Zemplén forest is ecologically unique because up to 95% of its oak trees are Quercus petraea.

The casks that we used to mature our Isle of Raasay Hebridean single malt were made from Quercus petraea that grew in Hungary and is why we refer to it as Hungarian Oak. These oak casks were originally used to mature oloroso sherry. We purchased them from the bodega after they emptied the casks. We then filled them with our new make spirit and matured them in our dunnage warehouse on Raasay.

We have also used Quercus petraea that grew in France and the flavour profile is very different from the Quercus petraea that grew in Hungary.

Isle of Raasay Hungarian Oak

Oak species maturation pack