Explainer: alcohol begins with yeast, so why don’t we talk about it more?

Fermentation vats at Woodford Reserve.

Grand copper stills. Ancient mineral spring water. Oak cask finishing. Terroir. Time. 

These are the things we hear when we talk about fine spirits. We hear about the craftsmen and women and the generations of distilling knowledge handed down from parent to child. The height of the still, the length of the line arm, the position of a barrel in a rickhouse.

And we hear about the distiller, the cooper, the master blender, and how important it is that they bring their refined palates and savoir-faire — their very life-force — to bear on the fine spirits in our glasses. It’s the romantic stuff you read in the brochures. 

But what if the really crucial work isn’t performed by humans? What if all that beauty is created not by the hand of man, but by the microbiological maestros working away inside the wort, multiplying, consuming, excreting — and creating?

There’s quite the orgy going on inside, so let’s dive in.


What is yeast?

Yeasts are single cell eukaryotic microorganisms, have been around for hundreds of millions of years, and belong to the fungi kingdom. Though we’ll be covering a few species of yeast here, there are 1500 or more different species of yeast out there (some of which, like Candida auris, you want to avoid — it’s developing quite a resistance to anti-fungal drugs it seems and can kill you).

We’re talking about far more benign yeast species here, the ones primarily responsible for baked goods and alcoholic delicacies.

And the big dog among those is Saccharomyces cerevisiae. Known also as baker’s yeast, humans have been mucking around with the stuff for around 5,000 years to get a buzz on.  It’s the same yeast strain you’ll see most winemakers employing, and it is used to make a lot of beers as well.

When it comes to making beer, the type of yeast you use depends on the style of beer you want to make: if it’s ale you’re after, you tend to use S. cerevisiae — it does its work at the top of the wort, which is why ales are described as being top-fermented. 

Lagers are often made with a hybrid of Saccharomyces cerevisiae and a variety called Saccharomyces eubanyus, which is known as Saccharomyces pastorianus.

But these yeasts can’t perform their duties just anywhere. They must, much like us, have the right conditions to thrive.

For yeast to do their work, water must be present, along with sugars, some oxygen, and other nutrients and trace minerals — this is the stuff they feed upon, the stuff that gives them energy to multiply. But they also need the right temperature. Saccharomyces cerevisiae does best in acidic environments of around pH 4.5-6.5, and at temperatures of 20-30 degrees Celsius. Saccharomyces pastorianus, on the other hand, does better in cooler temperatures, somewhere in the order of 8 to 15 degrees Celsius.

These yeasts can feed on a range of different sugars, depending on the base material and the ultimate alcoholic beverage desired. So for rum production, they’ll feed on sucrose from molasses and sugar cane; with wine and fruit brandies it’ll be glucose and fructose; for agave spirits it’s fructose; and for beer and malt whisky it’s maltose.

It’s not just alcohol

We know the equation: yeast + glucose -> alcohol (ethanol) + carbon dioxide. To put it into words, yeast converts sugar into alcohol and carbon dioxide. Right?

But that’s not the only role yeast plays in the fermentation of delicious alcoholic beverages. Depending on the strain of yeast the producer uses, you’ll get some alcohol created, sure, but it is also responsible for a host of other compounds that create texture and mouthfeel and aromas and flavours. 

These compounds are also created when yeasts convert sugars to alcohol — they create carbon dioxide along with glycerol, and at lower concentrations, esters, higher alcohols, organic acids, and aldehydes, all of which contribute to the quality of the final product and its aroma and flavour.

Glycerol primarily contributes mouthfeel and texture to wines and beers; esters contribute the floral and fruity aromas desirable in beers, wines and spirits; and higher alcohols, like fusel oils, are congeners desirable in beer and spirits like whisky and rum.

The process doesn’t always create good stuff, either: it creates vicinal diketones, which are two words as incomprehensible to us as they are to you — either way they’re responsible for unwanted rancid butter and butterscotch flavours.

Not all strains of Saccharomyces cerevisiae perform the same, however. Some, like the commercial types employed for making neutral and highly rectified spirits like gin and vodka, are better suited to the task with a higher tolerance for ethanol, which creates fewer congeners.

And it’s not only Saccharomyces varieties that can do the job of converting sugar to booze. There are a range of other yeasts, with names like Dekkera, Hanseniaspora uvarum (found on grapes and in grape must); and Dekkera bruxellensis (which you may know as Brettanomyces, often considered to be a taint in wine but a desired yeast for Belgian lambic beers and some kombucha), to name but a few. 

Wild yeasts, proprietary yeasts

The vast majority of alcoholic beverages these days are made using either commercial or proprietary yeasts; for instance, Bacardi’s famous yeast, La Levadura Bacardi, is the same yeast strain they’ve used since 1860. That’s a proprietary yeast. American whiskey makers often follow the same principle — Wild Turkey, Jim Beam, Jack Daniel’s and Maker’s Mark have all used their own particular strain of yeast for many decades.

In the wine and beer industries, and particularly in the Scotch industry, producers will use commercial yeasts provided by companies that specialise in this area – one of the biggest suppliers in the world is Lallemand, a global company (with a branch in Australia) that sells variants like LalBrew Belle Saison, a Belgian-style yeast. Take a look at their online catalogue and you’ll see how different variants of Saccharomyces can encourage different flavours and aromas.

In reality, however, it’s unlikely that, even when using proprietary or commercial yeasts, those are the only yeasts in the mix; there are yeasts in the air, on the walls of a distillery, on the raw materials used for distillation and on our clothes and skin. The buggers are everywhere. 

But not all yeasts can thrive in all environments, and that’s why using a commercial Saccharomyces cerevisiae will get the end result you want — it’s too strong and won’t allow the other yeasts to propagate and survive, in a kind of microbial game of Highlander.

The real wild west of the yeast world is when you get to wild yeast-fermented drinks, like mezcal. These yeasts live on distillery walls and vats and on the agaves, and make claim to a sense of terroir in spirits. That particular microbiological environment would be impossible to replicate anywhere else.

Yeasty toys

Glenmorangie Allta
Glenmorangie Allta, the latest in the limited private edition releases from the distillery, uses a special strain of yeast. The yeast, Saccharomyces diaemath, was discovered on their distillery grounds, and was unknown before Dr Bill Lumsden discovered it. Moet-Hennessy

Bacardi Carta Blanca
Bacardi has been using the same particular yeast since they got started back in 1862. They call it La Levadura Bacardi, and it is kept in multiple locations across the world. La Levadura is a key component of the Bacardi’s unique taste profile, what makes Bacardi taste like Bacardi. Bacardi-Martini

Nikka Coffey Malt Whisky
In Scotland, many distilleries use the same yeast, but things are different in Japan. Dave Broom has written before that Nikka uses a combination of five different yeast strains in their whisky. Nikka Coffey Malt offers a robust dense texture with notes of cinnamon, clove and lemon, and a long finish with a blend of rich oak, tobacco and mild chocolate. Asahi Premium Beverages

Maker’s Mark
Maker’s Mark uses a custom yeast variety that is some 150 years old — it is said that the yeast is responsible for a light, fruity character. Wood and oak, along with vanilla, caramel and wheat characters on the nose; the palate is balanced, with some sweetness countered with caramel, vanilla and fruit notes. The finish is smooth and subtle. CCA/Beam Suntory

Wild Turkey 101 Proof Bourbon
Wild Turkey is another bourbon distillery that proudly champions the specific yeast strain they use. It has been around since 1954, and is said to be responsible for a nutty and spicy character in Wild Turkey’ whiskeys. Campari Australia