Why yield to yeast?
The story of yeast strains might not be the most engaging one you hear on a distillery tour. But that could be set to change, finds Tom Bruce-Gardyne
“The yeast consideration has been pretty low on the agenda for many distillers. They simply regard it as a raw material for producing alcohol rather than flavour”
PROFESSOR GRAEME WALKER
“What’s yeast ever done for us?” cried Professor Graeme Walker at that start of his 2015 ‘Give in to Fermentation’ show at the Edinburgh Science Festival. Describing yeast as a “very sophisticated unicellular fungi” he listed its various achievements under the letter B. “It’s given us brilliant Nobel prize winners, bread, beer and all alcoholic beverages, biofuels, biopharmaceuticals and billions of pounds!” he declared. “Is there another organism in the world that makes more money?” “Simon Cowell!” shouted someone from the audience.
As a professor of zymology, the science of fermentation, at Abertay University, Graeme believes the whisky industry has been missing a trick. “For so many years the yeast consideration has been pretty low on the agenda for many distillers,” he says. “They simply regard it as a raw material for producing alcohol rather than flavour.” However, he senses that might be changing and cites the example of Glenmorangie Allta, released in 2019.
A decade earlier Dr Bill Lumsden, then Glenmorangie’s distillery manager, worked with the yeast supplier Lallemand to isolate some wild yeast found on barley growing in a nearby field. It was propagated in a lab and pitched into the wash. Once distilled, according to Dr Bill, it lent “floral, bready notes” to Glenmorangie’s new make spirit, which typically has “more herbal, fruity and pear drop aromas”.
DEATH AND FLAVOUR
Wild yeast is everywhere and explains why fermentation is a wholly natural phenomenon. Our earliest ancestors had no idea of its existence, but they could see its effects as it gorged on the sugars in fruit and grain, excreting alcohol and carbon dioxide as by-products. The bubbles of CO2 were the only evidence that anything was happening, but it can be dramatic if you’ve ever encountered a rocking washback in full ferment at a distillery. In what’s been dubbed a “heroic act of self-sacrifice” the yeast cells die, but even in death they add flavour to wines like champagne.
With wine you can use the wild yeast on grapes, but it’s washed off barley during the malting process, so the whisky industry relies on cultured distillers yeast. “There will be lots of distilleries using the old DCL M-strain yeast,” says Ian Palmer of InchDairnie distillery. “They’re happy with the product, it’s built into their economics, into how the distillery operates – so why change it?”
Crucially the strain helps define the distillery character, which is why Glenmorangie and all the established names in single malt have no intention of switching yeast for their core range. There is no constraint for newcomers like InchDairnie however. “The opportunity lies with those who don’t have a history,” says Ian. “Basically, people like me have no baggage, so we can use different yeasts to get different flavours.” This year he’ll be using seven of them for InchDairnie’s grain, peated and rye whiskies and for four seasonal malts.
“There will be lots of distilleries using the old DCL M-strain yeast … it’s built into their economics, into how the distillery operates – so why change it?”
“The opportunity lies with those who don’t have a history … people with no baggage, so we can use different yeasts to get different flavours”
Pictured: Dornoch owners Simon and Phil Thompson experiment with fermentation in their small but pioneering distillery
“The industry is a bit more reserved about disclosing any findings. We’re hoping to be a distillery that’s a little more open about things”
The dominant yeast used in brewing, baking, distilling and winemaking is Saccharomyces cerevisiae, but within this species are far more strains than the three typically used by whisky-makers. In beer, “there are thought to be thousands of ale yeast strains,” says Professor Graeme Walker. Beyond lie an endless variety of “non-Saccharomyces” or “non-conventional” strains of wild yeast, whose suitability for whisky is being investigated by Martina Daute, one of his PhD students, in a collaboration between Abertay University and the Scotch Whisky Research Institute.
She has already found a few strains that show promise, combining interesting flavours with an alcoholic yield to match commercial distillers yeast. Besides ethanol, the hard-working yeast cells produce hundreds of flavour compounds, or metabolites, some of which make it over the still. Different strains will give you different combinations to shift the new make spirit in a heavier, spicy direction or one that’s lighter and fruitier, for example.
PLAYING WITH FLEXIBILITY
Preserving those points of difference through the years of maturation is key, as Vicky Muir-Taylor of the Port of Leith distillery explains. “There’d be little point in putting time and effort into ‘wacky’ and ‘alternative’ fermentations, especially if you decide to take a bit of a yield hit, and getting a really funky or fruity wash if you end up maturing the spirit entirely in relatively fresh casks or finishing for a long time in something strong like a first fill ex-sherry cask.”
Port of Leith has delved deep into fermentation with over 20 different yeast strains to create a unique series of new makes, and right now Vicky and her colleagues are deciding which combination of casks will work best. Compared to the established players, she believes: “As a start-up and smaller distillery, I do think we are going to have a lot more flexibility.”
She says the Scotch whisky industry is doing plenty of research on yeast behind the scenes but that it’s “just a bit more reserved about disclosing any findings. We’re hoping to be a distillery that’s a little more open about things.”
“Different strains will give you different combinations to shift the new make spirit in a heavier, spicy direction or one that’s lighter and fruitier”
Pictured: Vicky Muir-Taylor of the Port of Leith distillery
There’d be little point in putting time and effort into ‘wacky’ and ‘alternative’ fermentations, especially if you decide to take a bit of a yield hit”
YIELD vs FLAVOUR
Professor Graeme Walker reckons most distillers want “a fine balance between the final alcohol yield and flavour development,” certainly for malt whisky. That said, the drive for efficiency suggests yield probably wins out, at least until the spirit is left to evaporate and feed the angels in an expensive second-hand barrel in some dank warehouse.
“If you go for flavour, you will lose efficiency,” says Ian Palmer, who knows all about the latter from his days at the Invergordon grain distillery. You might also sacrifice efficiency by prolonging the fermentation to around 60 hours, but “you can then get so-called ‘desirable’ lactic bacteria that are known to produce interesting flavour and aroma compounds,” says Graeme.
As well as depressing the accountants, this whole subject is unlikely to thrill the marketing department charged with promoting an invisible fungus. Vicky admits: “It is a bit of barrier because when you start mentioning yeast people do tend to glaze over a little, so it’s a new challenge to make it sound more engaging.”
But it can be done – and done magnificently, as the good professor proved with his ‘Give in to Fermentation’ gig five years ago.