Express Yourself With Brewers Yeast

Yeast is the Perfect Way for Brewers to Express Themselves

Over the years a number of brewers have told me something along the lines of: “brewers make wort, yeast makes beer.” And while it’s a very romantic notion, I don’t believe a word of it. 

Yeast, like a paintbrush in an artist’s pocket, or a chisel in a sculptors, is a tool; a means of expression that can allow hops and malt to sing, just as it can build in evocative flavour of its own design. It’s one of the most exciting, expressive ingredients in a brewers arsenal, and there’s never been a better time to experiment with different strains and see what flavours they can offer.

There are several reasons why I don’t agree with the notion that “yeast makes beer.” This is largely due to the many variables available to a brewer or cellar manager and how these can produce different results, even from a single strain. Temperature is a good starting point, and even small variations can produce everything from clean fermentations through to those that are ester-heavy, expressing flavours from strawberry, to banana, to stone fruit. Smoky, or clove-like phenols are another byproduct of fermentation, and while not always desirable they can be wonderful when expressed in certain styles. 

Wort composition is another way of affecting how yeast will behave. If higher levels of dissolved oxygen or lipids are present this can inhibit ester production. Other compounds like zinc or high concentrations of sugar can encourage yeast to produce them, as can the presence of free amino acids. The shape and size of a fermenter will also influence how yeast behaves — Brasserie de la Senne in Brussels is known for using wide, flat fermenters because they believe it helps keep their yeast happy and healthy. This is true, in that environments with lower hydrostatic pressure (literally the pressure exerted on fluid by gravity) will be more hospitable for yeast. 

Another, arguably simpler way of affecting fermentation to get specific results is by selecting a specific yeast strain. Handily, there are now several labs throughout the world heavily invested in commercial yeast production such as Fermentis, based in Lille, France, a stone’s throw away from the Belgian border. Like many of their competitors they produce an eye watering range of strains, some that suit certain beer styles such as German weissbier or phenolic strains for certain Belgian or English styles. And then there are workhorses, like the good old Fermentis S-04, what you might call a “clean yeast” as it lets hops shine through in modern IPAs. This is just a handful of what’s on offer too, demonstrating how versatile experimenting with different strains, and indeed how you treat them, can be for your beer. 

As you can see, fermentation is not something that is simply ignored by the brewer and left to these millions of microorganisms. Yes, they do an important job in beer making, but if that beer is good, it means the brewer in charge has done a good job of being their boss. 

There are other, fascinating ways in which yeast can influence the flavour of beer, or in some instances, develop an entire house character a brewery can build (or break) its reputation upon. Harvey’s Brewery of Lewes, Sussex, still reportedly uses a pitch that was sourced from the John Smith’s Brewery of Tadcaster, Yorkshire in the late 1950s. Since then the yeast has evolved and mutated, creating the “tamed wildness” that can be tasted in every sip of its beer. 

According to some sources, the reason for this is that Harvey’s house strain contains a culture known as Debaryomyces hansenii. Now, you might have heard of Brettanomyces, which has been popularised due to its use in the legendary Trappist beer, Orval, and is now widely used in brewing thanks to the funky, fruity flavour it has the capacity to produce. Debaryomyces is more commonly found in saline environments such as on maturing cheese, or curing charcuterie. In Harvey’s beer, however, it reportedly adds that special, can’t quite put your finger on character that drives fans of its beers wild, myself included. 

Manchester’s J.W. Lees Brewery is another that is indebted to the longevity of its house strain. Whereas most modern breweries may only repitch wet yeast around say eight or 10 times, Lees has been repitching for over 5000 generations. Head brewer Michael Lees Jones recently told Geterbrewed during a tour that brewers were even brewing small batches of beer during lockdown in order to keep their prized strain healthy and happy – such is the value it provides to the character of its beers. It’s one you can easily experience too. Pick up a pint of Lees Bitter or Dark at one of its many Manchester pubs and you’ll quickly identify the dark fruit character that makes its beers taste so expressive, while also retaining an inherent drinkability.

Only one other brewery has had the fortune of using Lees house strain; fellow Manchester outfit Cloudwater. As you might expect, they experimented with it, investigating its behaviour as it fermented out an 8%, double dry hopped (DDH) IPA. What was fascinating about this particular beer was not how it imbued it with the expected Lees house character, but instead how that yeast behaved as it interacted with the various compounds found in hops. By dry-hopping during active fermentation, hop varieties that would normally give a beer lemon peel and orange zest characteristics were being broken down and reformed into those that produced notes of peach and apricot. Although it must also be said that the inherent character that makes Lees beers so defined in terms of house flavour still managed to make its presence felt in the final beer, such is the strength of its character. As a yeast strain, it could be described as ‘tenacious’. 

While it’s still not a fully understood science, the process of transforming hop compounds through dry hopping during active fermentation is known as biotransformation. Explaining it properly would require a blog post of its own, but a very, very simplified way of explaining it would be that when the right kind of yeast, in the right conditions is presented with a flavour compound, it breaks it down, eats a little bit of it, and then puts the rest back together in a different shape. That’s biotransformation, baby!

Research into biotransformation is opening up more new ways in which brewers can experiment with fermentation derived flavours. One of these is the potential to unlock thiols, highly potent aroma compounds that exist in hops but are challenging to access. In order to access them brewers must use what is currently known as “thiolised yeast” which, through biotransformation, has the potential to express thiols in a finished beer. To explain thiols properly, the simplest thing to do is to look at wine, as many popular grape varieties also express them. New Zealand Sauvignon Blanc is a great example, as its dominant tropical and grassy aroma is the result of thiols present in the finished wine. 

As with biotransformation in general, it’s still not an exact process, and one that is still in the early stages of its development. It’s likely yeast developers and brewers will continue working on new strains and pitching techniques as they continue to try and unlock this latent potential that’s inside many modern hop varieties. What it does serve as is yet another example of how expressive and vital yeast is as an ingredient within beer. Something that’s a vital tool that helps brewers get the best out of their beer, and not a task that merely involves leaving millions of microorganisms to go about their business completely unchecked. 

– Matthew Curtis