The malted barley is weighed in 75kg batches and ground through a traditional four roller mill to make 6.825 tonnes of grist with a consistency of 16-20% husk, 70% ‘middles’ and 10-14% flour. The semi-lauter mash tun is charged with the grist and 28,000 litres of warm water at around 64°C. The mash tun takes about one hour to fill and this is then left to rest for around an hour, during which time, the husk settles to the bottom of the mash tun and the starch in the grist is converted into sugars.
After about an hour, the mash (or ‘wort’) is pumped through to the washback via a heat exchanger, which cools the wort to around 36°C and the dried yeast is added. The temperature of the wort entering the washback is then reduced to around 18 to 20°C.
When the washback is around half full, a second water is added to the mash tun at 70 to 72°C and this is also pumped through to the washback. This second water reduces the density of the liquid in the washback, providing a nicer environment for the yeast. Once the second water has all been pumped through, the mash tun is left with just wet spent grain husks which still have some residual sugars left on them. A third water is put through the spent grains at 90 to 95°C and is recovered to be used as the first water (sparge water) in the next mash.
Around three hours after the yeast has been added to the wort aerobic fermentation begins. After several more hours, the yeast will have multiplied to give about four times its original volume. The initial volume ratio is 35kg of dried yeast to 3,5000 litres of wort and this increases to around 140kg after reproduction.
When little or no oxygen is left in the wort and the yeast stops multiplying and anaerobic fermentation starts turning the sugars into alcohol, carbon dioxide and other trace products. The density (or ‘gravity’) of the wort drops rapidly as the alcohol produced is less dense than sugar and after around 50 to 60 hours after the addition of the yeast, the fermentation process is complete, resulting in a ‘wash’ with an alcohol content of 7.5 to 8.2% alc./vol.. The wash is then charged into the wash still for distillation.
Auchentoshan is the only Scottish distillery to triple distil all is production. A few other distilleries triple distil part of their distillation and then blend this with double distilled spirit, or make special products that are triple distilled with the bulk of their output being double distilled.
Triple distillation is not as simple as distilling the wash and then taking the result of that distillation and distilling twice more - although that essentially what happens. Those canny folk at Auchentoshan want to squeeze as much alcohol out of each distillation as possible due to economic, as well as green considerations. So where heads and/or tails are separated, they may be recycled to an earlier stage in the distillation of the next run.
Triple distillation at Auchentoshan broadly goes like this:
First distillation (in wash still): The entire distillate produced from the first distillation in the ‘wash still’ goes on to be redistilled in the second distillation which takes place in the ‘intermediate still’. No head or tail cut is made.
Second distillation (in intermediate still): Heads are not separated in the second distillation which takes place in the intermediate still but tails are and these are stored to be added to the charge of the next first distillation back in the wash still. The rest of the distillate produced by the second distillation goes on to be redistilled a third time in the ‘spirit still’.
Third distillation (in spirit still): In the third distillation the heads and the tails are separated to leave a spirit ‘heart’ which will go onto to be aged in cask to eventually be bottled as Auchentoshan. The heads and tails from the third distillation are put aside to be added to the charge of the next second distillation back in the intermediate still.
All three stills at Auchentoshan are steam coil heated and have external ‘shell and tubes’ condensers situated on the other side of the back wall of the still house - the wash still condenser being disproportionately large.
The amount of wash produced from each fermentation at Auchentoshan is sufficient to charge the wash still twice over, hence half the contents of the washback is pumped into the wash still. Alcohol starts coming off the wash still at around 46% alcohol and this falls to 1% by the end of the distillation, some 3 to 3½ hours later when the still is shut down. This first distillation produces a distillate of around 13% alc./vol. but the alcohol content in the low wines receiver is actually around 19% due to the addition of tails from the intermediate still.
The intermediate still is charged with the contents of the low wines receiver. The spirit starts to come over at around 70% and this is sent to the high wine receiver until the strength drops to 20% when the flow is diverted to the low wines receiver. The average strength of the spirit flowing from the intermediate still to the low wines receiver is 53% alc./vol.. However, due to heads and tails from the spirit still also flowing into the low wines receiver the strength is bolstered to around 55% alc./vol..
The spirit still is charged with the contents of the high wines receiver and distillation started. The first 5-10 minutes of this third distillation produces heads (foreshots) which are sent t0 the high wines receiver. When the strength of the run has dropped to 82.6% alc./vol. the quality of the spirit coming of the still is good enough to make the first cut and the flow is diverted to the intermediate spirit receiver (ISR). When strength of the spirit falls to 80%, the second cut is made and the flow diverted to the high wines receiver. The distillation is then allowed to run down to 1% as normal and the total length of distillation is usually around 7 hours. The ‘heart’ or ‘new make spirit’, i.e. the spirit collected between the first and second cuts in the ISR, is 80 to 81% alc./vol..
The only waste produced in each distillation (apart from lost heat and vapour) is the pot ale and lees which remain in the stills when distillation is stopped when the contents of the still are a mere 1% alc./vol..
Most Scottish distillers distil twice and most would say of folk like the Irish who triple distil that they get is right the second time. However, making Scotch over three distillations has some advantages if you seek to make a lighter spirit. The spirit produced is not just purer because the final distillate is of a higher strength (80-81% compared to 66-72% alc./vol. using double distillation).
At Auchentoshan the use of a intermediate still means the spirits still is charged at 55-56% alc./vol. as opposed to the typical 23-28% alc./vol. charge for spirits stills in double distillations. Chemical analysis has shown that having a higher strength charge dramatically affects the separation of congeners from the heart (new make spirit).
Highly volatile congeners that distil first (heads): acetal and ethyl acetate are in competition with ethanol to escape so congeners take longer to distil from the sprit still compared with wash still. An analogy is that these molecules are people in a crowd and although their high boiling point makes them desperate to find the exit, the crowded still means many of their number are trapped and so end coming out the still with the ethanol in the heart rather than ahead of the crowd with the rest of the heads. The higher charge strengths of triple distillation largely eliminate this affect.
Some other congeners do not like water and are more attracted to ethanol. So, even though congeners such as furfural and methanol are more volatile than ethanol, they may stay in the pot longer due to their attraction to ethanol. They are like brothers and sisters that can’t bear to be separated and need more energy to be prized apart. When the ethanol concentration drops to a critical level and there is relatively more water in the pot, the congeners will then escape very quickly to get away from the high water content. At Auchentoshan the charge strength is so high that the second cut is made before that critical level is reached. Methanol levels at Auchentoshan are around four parts per million (ppm) as opposed to typically five ppm after double distillation.
At Auchentoshan, the distillate comes off the third still at a high 82% alc./vol.. Jeremy Stephens, Auchentoshan’s Head Distiller, argues that Auchentoshan is much cleaner with a lot of the heavy flavours and harshness already removed by the time the new make spirit goes into the cask - so the character of that cask comes through earlier. In order words, Auchentoshan is lighter and so ages quicker.
Maturation & blending
The new make spirit is sent by tanker to the company’s facility in Springburn, Glasgow where it is diluted from its unusually high 81% back to the industry standard 63.4% alc./vol. for cask filling using highly purified water. A proportion of these casks are sent back to rest in the distilleries warehouse but the majority are aged in bonded warehousing in Springburn.
Like most Scottish distillers, the majority of casks used are ex-American whisky casks - both hogsheads and butts. Auchentoshan also use sherry casks, both Oloroso and Pedro-Jimenez. After the successful release of a 1999 Saint-Julien Bordeaux wine cask matured limited edition, the distillery is also laying down more wine casks. The light style of Auchentoshan seems particularly suited to wine cask maturation.
Cask selection and blending lies takes places at the company’s Springburn warehousing and bottling facility.