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The Fundamentals of Fermentation

November 19, 2018

Yeast is one of the three raw materials permitted to make Scotch Whisky but for some reason doesn’t get spoken about as much as barley or water.

Specially developed yeast is used by distillers in the fermentation process to convert sugars into alcohol.  During the fermentation process yeast is added to worts (a sugar-rich liquid) and left to ferment for varying periods of time.

There are two phases to the fermentation; the lag phase and the budding phase.  Once the yeast is added to the worts it will take time to adapt to its new surroundings, this time is known as the lag phase and normally lasts for less than 12 hours.

Once the lag phase is complete the yeast begins to ‘bud’, a process of asexual reproduction.  As the yeast reproduces it creates alcohol and amino acids, the starting point for the development of complex flavours.  Both the fermentation time and the strain of yeast play a role in the development of flavour.



Fermentation Time

We typically categorise fermentation times into 3-time brackets; short (less than 60 hours), medium (60 -75 hours) and long (more than 75 hours).

Typically a short or medium fermentation time will produce a malty flavoured spirit.  If the wash is allowed to ferment on beyond 75 hours, as we do at Kilchoman, the amino acids build within the liquid, adding layers of floral, perfumed sweetness and fragrant citrus notes.  Our 85 hour fermentation time allows the yeast to fully ferment, creating a distinctly floral spirit balancing peat smoke and maritime influence with lighter citrus character.


Yeast Strains

There was a time when all distillers of scotch whisky all used the same yeast strain which was DCL M-Strain , this was due to its ability to break down maltose sugars and produce good alcohol but also flavours that were associated to Scotch Whisky. This strain is still used today by distillers, however modern strains such as MX, Mauri and Anchor/Bfp are now also available.

We ferment exclusively with Mauri yeast, a bagged live yeast which was chosen from four test strains.  We found the Mauri yeast created the best balance of flavours, adding layers of citrus sweetness and tropical fruit.


As well as the Yeast that is used in the fermentation process the materials of the Wash Backs are also up for debate. Originally all wash backs were made from European Larch, Douglas Fir or Oregon Pine. These were all used due to their long knot free planks. Recently distillers have been using stainless steel wash backs as they require far less maintenance and are a lot quicker and easier to clean. However the debate as to which is better rages on with advocates of wooden wash backs saying that the wood helps provide a slightly sweeter wash.


Whilst wooden wash backs are beautiful to look at, each is different and can react in varying ways over their lifetime.  Here at Kilchoman we have six 6000 litre Stainless Steel wash backs.  The choice of stainless steel ensures total consistency across all batches no matter the time of year or number of times they’ve been used.

So there you have it, our Fundamentals of Fermentation.  Keep an eye for more in-depth posts coming soon.





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