Brewer’s Yeast: The employee that works 24 hours a day

words: patrick jodoin | illustrations: denis routhier

When I’m drinking a few beers with my friends and the topic of conversation ends up on the beer we’re drinking, these discussions are often dominated by the subject of hops. Understandably so: hops are responsible for a lot of a given beer style’s flavour and aroma.

But we almost never talk about yeast.

Why is that? Could it be a general lack of knowledge about yeast’s role in the creation of beer? A lack of awareness that yeast plays a major role in the way beer tastes?

To answer these questions I spoke to the person I always turn to when I need in-depth information about beer, my colleague at Beau’s, our brewmaster, Matthew O’Hara.

“It’s important to emphasize just how crucial a role yeast plays in beer’s creation,” said O’Hara. “I view yeast as the lifeblood of a brewery. Without yeast you wouldn’t have fermentation, and without fermentation you wouldn’t have beer.”

When we sat down to talk about yeast, O’Hara and I were joined by Beau’s QA/QC lab manager, Alex McKinnon, who studied yeast for his Masters degree in Wine Biotechnology at the University of Stellenbosch, South Africa.

After speaking to O’Hara and McKinnon I hopped on a phone call with Angus Ross, co-founder of Escarpment Laboratories in Guelph, Ont., which produces enough yeast every week to make approximately 300 to 400 hectolitres (between 50,000 and 70,000 Canadian pints) of beer.

I’ve broken down these conversations into some sub-categories below. Read on to learn all about yeast, the hardest working employee at any given brewery.

What is yeast?

Yeast is a fungus, closely related to mushrooms. It is a single-cell eukaryotic organism. Humans are also made up of eukaryotic cells, but thousands of thousands of them. This is why yeast is often used as a model organism in research in which a facsimile of human genetic makeup is required, such as cancer research for example, in place the cells of humans, pigs, mice, plants etc. Yeast is a useful tool for modeling how humans work, so the majority of study into yeast is genetic research.

“It’s the first domesticated organism,” said McKinnon. “It’s found everywhere in the environment. Because it eats sugar, it’s found anywhere that sugar might be: flowers, on fruit, even on barley. Over the years we’ve selected yeasts for brewing that are alcohol-tolerant so they can create higher levels of ethanol, and ones that are easy to work with.”

“You can think of yeast in pretty similar ways to domesticated animals,” Ross explained. “We’ve been able to mold this creature into something that is useful for us.”

In terms of the brewing process, what does yeast do?

Breaking it down into basic steps, brewer’s yeast creates ethyl alcohol by converting sugars into carbon dioxide gas. Yeast is pitched (or added) to the wort ( unfermented liquid malt, hops and water) to create beer.

Fermentation is the “party element,” as O’Hara put it.

“I would liken yeast to the hardest working employee of a brewery,” said O’Hara. “This is really where the magic springs from: a yeast’s ability to metabolize the sugars that we’ve created and throw off this amazing array of flavours and aromas, and then create the CO2 and ethanol.”

“It’s the employee that works 24 hours a day,” agreed Ross.

We know that yeast creates alcohol, but tell us more about flavour: How exactly does yeast influence a beer’s flavour?

This is where, according to O’Hara, yeast doesn’t get enough credit. Yeast lends character and complexity to beer. Further, different strains impart different characteristics. In brewing, the yeast selected is a key component to most different beer styles. A saison, for example, cannot be created without a saison yeast. It is the defining element of that beer style.

“In the beer world we’ve been able to create different strains of yeast that are well-suited to make different  kinds of beer,” said Ross. “There are yeasts of Belgian origin that produce various distinctive flavours, there are lager yeasts that ferment in certain ways, and ale yeasts from other parts of the world that will produce fermentation kinetics, flavours and aromas that define certain styles of beer.”

Here are some common yeast strains and the flavours they’re known for:

• Belgian yeasts: Belgian strains of yeast are known for producing complex spice and pepper characteristics in beer.
• English ale yeast: English ale yeast is known for producing fruity esters in beer.
• American ale yeast: American ale yeast typically takes a back seat to the malts and hops and allows them to define flavour.
• Weizen: Weizen is a German strain known for its banana and clove flavour.

Check out Escarpment Labs’ strain collection for an eye-opening list of yeast strains and their characteristics!

“A lot of the classification of yeast is based on a list of carbon sources like  glucose fructose, ribulose, and whether or not the yeast consumes it and can thrive off it as a single source or not,” said McKinnon. “Belgian yeast and English ale yeast are technically both saccharomyces cerevisiae, but any brewer can tell you that the flavour compounds that they throw off are dramatically different.”

For extra context O’Hara offered the following: “If we took the same wort that we would use for a Lug-Tread fermentation and instead of using a German ale yeast decided to use a Hefeweizen yeast, we would have a totally different beer that would taste and smell like bananas, bubble gum, and cloves. But the beer would in every other sense be identical: same malt, same hops.”

Furthermore: “There is new research that shows there are interactions between some strains of yeast and different hop flavour compounds,” said Ross. “You can sometimes modulate what the yeast does based on how you hop your beer — which is fascinating.”

How long have we been studying yeast?

The study of yeast in a brewing context is a relatively new thing. “The timeline for us even knowing that yeast even existed in alcoholic beverages is not that long,” said McKinnon, “compared to the 2000+ years we’ve been using yeast to ferment things.”

It was Dr. Emil Christian Hansen, working at Carlsberg Laboratories in Copenhagen, Denmark, who was the first to purify yeast in 1883. This discovery put an end to “beer sickness,” or contaminated beer from unwanted bacteria, a result of unpredictability in brewing.

Dr. Hansen was the first to postulate that it was in fact microorganisms that caused wine and beer to ferment. Prior to Dr. Hansen’s work at Carlsberg, brewers didn’t know that yeast was an organism that they needed to keep alive.

Needless to say, to this day yeast requires a lot of TLC: “We as brewers have to give yeast a good home to maintain its health and integrity,” said O’Hara. “This means keeping things clean, and fostering a nutrient-rich environment for yeast to do its thing.”

“Some of the yeast strains we’re using in our beer have been cultivated for hundreds of years,” said McKinnon. “It has taken people caring for these yeasts and keep them going generation after generation that has allowed us to use them.”

Lager strains today can cope with cooler temperatures because of the practice in Germany (Middle Ages through 1800s) of only brewing during colder months to avoid the contamination risks of brewing during summer; then having lagering (cold aging) take place underground in beer cellars.

“If the last German lager yeast disappears, for example, it is extinct,” he continued. “It is really cool to think that we’re using something that people have been using for thousands of years and keeping alive.”

McKinnon: “If you want to up your homebrewing game from mediocre to something you’re super proud of, don’t just take the yeast packet. Seek out other yeast strains and try them out. They have a huge impact. You’ll find ones that work well for you in the styles of beer you like to make, and you’ll find ones that don’t. If you can find liquid yeast that’s probably better than freeze-dried yeast.”

Recap

The next time I’m around the kitchen table with friends and the conversation gravitates to beer — as it often  does — thanks to these informative and fascinating conversations with Matthew, Alex and Angus, I’ll be able to delve a little deeper into the science of beer: from fermentation to yeast flavours and aromas, and everything in between. After all, the employee that works 24 hours a day deserves a little credit.