Our approach to Fermentation


Fermentation is an integral part of the distillation process. It takes place after ‘mashing’, where we’ve harvested barley, malted it, milled it and filled it into our mashtun. Here we add hot water to activate enzymes, converting starch to sugar. The sugar-y water is taken from the mashtun, where the fermentation process allows yeast to consume that sugar, in turn releasing alcohol as a by-product and more importantly, flavour! The next stage is distillation.

Our approach to fermentation at Bruichladdich is characteristic of how we work. It’s traditional, taking place in all wooden vessels (washbacks), which are constructed onsite by a team led by time-served coopers and no other technologies. It’s given time, a minimum of 65 hours, and up to double that long, if necessary. It has people as its lynchpin; the fermentation is judged by human beings taking manual measurements and giving the liquid their attention, using all their senses. They monitor its transformation from wort, sugar-y water, to wash, a cloudy 7% alcohol jam-packed with organic chemical compounds and esters. It’s a chemical process, with correct temperatures and volumes that optimise the reactions taking place, the management of which is preserved exactly by one generation of mashmen teaching the next. Their tools are a hydrometer, a “dip stick” (10 foot ruler which gives them the liquid depth and therefore its volume), flasks, and our 6 60,000 litre washbacks with slide-over lids. 

If you look at the way we deal with fermentation as a contributor to the flavours in whisky, however, the approach is not like us at all! No continual enquiry like we have over barley variety, how it is farmed, when it is harvested, where precisely it was grown, nor pushing the boundaries like we do with our bold maturation decisions or the types of casks we obtain. Why? Continuity, for now…

Yeast variables

There are many types of yeast – brewers (held up for more flavour) or distillers (for more alcohol), dried or fresh, fast or slow, cultivated or wild – and we have been through several options in the past. We’ve conducted controlled experiments with two different strains of dried yeasts over the past few years, but our mainstay is a combination of two live, wet yeasts, to which we always return. Why?

The two yeasts are described on our tours of the distillery as “a sprinter” which starts off the reaction, and “marathon runner” that keeps it going. We always use the same quantity of yeast, same types, from the same supplier, to ferment the same volume of wort in the same 6 washbacks. 

Allan Logan, Production Director, explains, “We’re trying to get the flavour from the malted barley through the wash that we can carry through into the distillation process. There are flavours from the spent yeast as well, these added flavours are important to us, you know, we’re not chill-filtering our whisky. But the barley is the main raw ingredient, and one that we’re really really interested in and committed too. If people are buying an Islay barley from us, we want them to be able to taste the difference that that barley makes, or that those farms make. So the yeast strains have become our one constant.”

This is Bruichladdich, though; don’t rule anything out. “Our exploration is not done,” says Allan. “We may have the ability to continue to controlled experiments with different yeasts in the future.”

The tun room tools

What goes on during fermentation?

What happens during fermentation is that yeasts, which are micro-organisms, break down sugars into alcohol and CO2, producing heat. The fist-thick staves of our Douglas Fir (aka Oregon Pine) washbacks are a much better insulator than 5mm stainless steel. Allan again, “During fermentation, the yeast generates its own energy, and its own heat. It’s important to have a stable environment for that to happen, because it happens naturally. It has its own life cycle, and we don’t want any interference with that. It’s temperature that allows the yeast to go to the next stage, then finally when it reaches about 30, 32 degrees, it dies off. You want it to always go through its full fermentation, so the rate of that temperature rise is important.”

Wooden washbacks

The type of trees used to make the washbacks, Douglas Fir, are known for their straight long trunks. The wood is relatively free of knots, which would be a weakness. Actually at Bruichladdich, right on the seashore, it’s the galvanised hoops around the staves that perish before the timber does. It lasts about 60 years. In March 2020 we completed the cycle that we began in 2002 of replacing all 6 in our tunroom with new ones, with the help of Ron Lowe of Dufftown.

Wood carries some burdens too though; in a word, cleaning. It’s a good environment for microbial life, which makes the yeast very happy through fermentation, but, for Allan and his team, “There’s always a fear, I suppose, with wood! That’s the reason why we steam the washbacks every time. So, we sterilise the wood by steaming it. After it’s emptied we clean it out with the hot hose, and then we’ll steam it for about 20 to 30 minutes so that it’ll be sterile, killing any bacteria or anything that would be potentially there.

So that’s it for fermentation. Worts and all.


Further Reading

Better transparency about ingredients >>

Building a new washback at Bruichladdich >>

Meet “Tug” Wilson, the gauger >> 

Compound Chemistry’s infographic about  The chemistry of whisky



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