Yeast - The Heart of Brewing - Sheep in Wolf's Clothing Brewery

In the UK, Northern Europe, and many other parts of the world, drinking beer is merely a part of daily life. You can have a beer with your mates at home or the pub, with dinner, or while sitting by a toasty fire. Hell, you may even have one with breakfast in places like Munich if you desire.

Most of us don’t sit with a glass of still or sparkling water and wonder how it ended up in our glass. And much the same, when we crack open some fermented concoction of barley and hops, we don’t necessarily ponder its origins. 

But these days, many of us aren’t just looking for something tasty. We also want to know it’s a complete journey, from farm to table. Beer has its four main ingredients: malt, hops, water and yeast. 

We can sit around all day arguing about which component is most important. But I’m gonna save us a lot of time by stating the obvious, it’s the yeast stupid!

What is Yeast?

Yeast is a single-celled microorganism classified as a fungus. This means that yeast is related to that delicious blue mould on the loaf of bread you’ve been meaning to throw out! And also closely related to those tasty-looking but possibly lethal mushrooms you brought home after a walk in the woods. 

Yeast originated hundreds of millions of years ago. Today there are over 1,500 different recognized species of yeast and counting. The word yeast comes from Old English gyst which means to “boil”, “foam”, and “bubble”. These terms refer to yeast as having magic-like properties.

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History of Yeast in Brewing

We don’t know how long humans have been cultivating yeasts for our own purposes. The earliest written documentation using yeast for baking dates back to ancient Egypt. While the oldest evidence of beer is believed to be a Sumerian tablet from 6,000 years ago! In brewing, yeast was passed from neighbour to neighbour and generation to generation through a wide variety of practices.

Throughout the middle ages, It was common to take a portion of “good” beer and reuse it to make the next beer. In parts of modern Scandinavia, we can still find a few farmhouse brewers using magic “yeast sticks' ' or whole dried bricks of yeast for inoculating their beers.  

Yeast in Modern Brewing

It was Louis Pasteur who first identified the existence of yeast and proved they were the cause of alcoholic fermentation. Before then, humans could only postulate about what biological machine was converting sugar into alcohol and carbon dioxide gas.

Louis only helped pave the way for modern brewing science with this discovery. But he is also responsible for identifying and disseminating yeast strains to many European breweries and distilleries that are still used today. 

What are the Characteristics of Brewing Yeast?

Baking yeasts and nearly all brewing yeasts are the same genetic species, Saccharomyces cerevisiae. But through centuries upon centuries of selection, these yeast have effectively been “trained” to be good at what they do. 

Brewing yeasts have a couple of important characteristics:

Alcoholic Fermentation duh right? The ability to convert sugars into alcohol and carbon dioxide is a must. But some types of brewing yeasts can metabolize more classes of sugars than others.

Flocculation this term refers to the ability of yeast to clump or bind together. This property allows the brewers to easily harvest yeast from a beer for reuse. And it also helps the yeast eventually drop out so that you can drink a beer instead of yeast slurry. 

Ale vs Lager

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In places like the US, Australia and continental Europe, lager and ale are equally referred to as “beer.” But this is not so much the case on ol’ Blighty. Here in the UK, the perceived divide between ale and lager is greater, with many going as far as separating the two as “beer” and “lager”. 

Semantics aside, ale and lager have several key differences. And it might surprise you that it mostly comes down to yeast. 



Saccharomyces cerevisiae

Saccharomyces pastorianus

Yeast clumps rise for top cropping

Yeast clumps drop for bottom cropping

Optimal fermentation temperature of 17-22 C

Ferments well at temperatures between 5-12 C

Fines well in beer

Does not fine well in beer

Cannot breakdown and use melibiose

Can use sugar melibiose

Although closely related, lager yeast is a separate hybrid species descended from S.cerevisiae and S. bayanus. Lager is typically fermented much slower and at much cooler temperatures than ales. And lagers will normally also be stored cold at nearly freezing temperatures for weeks to help clean up the flavours and appearance of the beer. 

Brett, Kveik and Beyond

Today, there are a wide variety of brewing yeasts available to professionals and homebrewers. These highly selected yeast strains allow for great diversity in fermentation behaviour and flavour production.

But things can get even weirder once we step outside of our S. cerevisiae comfort zone. Wild yeasts like Brettanomyces/Dekkera can be the stuff of dreams (or nightmares). Flavours such as leather, tobacco, barnyard, and horse blanket might not sound appealing at first, but in moderation, they can add a unique and interesting character to a beer. And of course, many strains like B. claussenii are known for their pineapple-like character. 

And thanks to the determination of people like Lars Garshol, we now have a full range of Scandinavian farmhouse yeast strains available to use. Many of these are descended from completely different species than normal brewing yeast and referred to locally as “kveik”.

For us brewers, kveik can be difficult to wrap our heads around. This is because most kveik completely breaks the rules of modern brewing practices. These yeast strains are often pitched in small amounts and fermented at ludicrous temperatures up to the high 30s and low 40s Celsius! 

Not to mention the general handling, harvesting and repitching of these yeasts which involves rough conditions like being dried out and a lack of hygiene. Kveik is other-worldly robust and has been known to completely ferment high strength beers in 24-36 hours. 

Possibilities with kveik are as endless as the imagination. Just a few common notes attributed to kveik fermentation are citrus, orange, banana, and other tropical fruits. 

Low Alcohol Beers Need a Different Approach

When it comes to low alcohol and nonalcoholic brewing, the learning curve is steep. At SWIC, we know more than most what is required to produce full-flavoured beers with less malt and fewer hops. But the keystone to making well-balanced low-gravity beers is to pitch the right yeast for the job. 

We believe that yeast is the heart of all brewing. For every beer we construct, we deliberate and select from a diverse range of yeasts to elevate our beers. Having used experimental and non-brewing yeasts in pilot and one-off brews, we know what works and what doesn’t. We are always constantly trying to improve, and we aren’t afraid of change. 

Whether it’s our Short Stack Wheat Beer or Lager Day Saints, our selected yeasts sit in the driver’s seat. This means that our beers take you on a 5-star ride every time! And you don’t even have to worry about surge pricing. Beat that “mobility as a service” provider that shall remain unnamed!

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