Beer School: What is Yeast in beer brewing?

We love hops as much as the next person. We think malt is underrated and we literally can’t live without water. But if we told you the most important ingredient in beer was the last one to be discovered? And is invisible to the naked eye. Without yeast, there would be no beer.

Yeast is, without a doubt, the most important ingredient in beer. In fact, speak to a brewer and he might well tell you that he doesn’t even make beer. The yeast does. Whether we talking fresh New England IPA or an Imperial Stout. Once the brewers added the malt, collected the sugary water and boiled it with hops. All you can do is create the best environment for yeast to work. When you are ready to brew be sure to check our How to brew your first Homemade Beer

Pouring liquid yeast into a glass jar.

The Yeast History

Brewers have spent millennia working to make life easier for yeast to ferment. Culminating in a sealed cone bottom temperature-controlled cylinders you see in most breweries. The different yeast works best under different conditions and produces different flavors. Choosing the right strain is as important as treating it right.

Yeast is one of the world’s great wonders. Too small to see until in huge concentrations it’s still a driving force behind all fermentations and baking. Two processes that lead to the civilization of the human race.

Even so, we’ve only known its properties and capabilities for about 150 years. Yeast is everywhere. On fruits and trees. On every surface. Even the air we breathe. There are millions of strains and they all have different properties when you brew with them.

A beer barrel, mug of beer, sack of hops and some wheat.

Discovery of Yeast

Until yeast was discovered fermentation was based on observation and superstition. We reused the same barrels and clay pots with no idea why. When Louis Pasteur discovered what he did. He opened the door to humans collecting, isolating, and propagating strains. The best ones for brewing have been slowly collected and produced in factories for commercial use.

Yeast is a single-cell organism that is able to convert sugars and nutrients into alcohol and carbon dioxide. From small beginnings in the test tube production of the yeast is ramped up fast in giant tanks that look a lot like fermenters.

The most common form of brewing yeast is called Saccharomyces. In fact, pretty much every beer you’ve ever tasted was made with one of the two families within that group.

Strain of yeast under a microscope.

How brewers choose yeast

Yeast also produces esters which are chemicals that have a very fruity character to them. There’s a lot a brewer can do to add complexity to beer with the right yeast. But even once the strain is chosen there’s more work to be done. Brewers use the yeast that has a profile they need and look to enhance them through a combination of population, temperature, time, and pressure.

A further way in which brewers can influence the flavors during fermentation is a relatively less understood process called biotransformation. Simply put this involves yeast not just breaking down the sugar in the malt. But also chemicals in the hops changing their character. Often resulting in a more pronounced hop aroma. In pursuit of those aromas and flavors, brewers have started dry hopping earlier in fermentation.

Combine that process with a yeast that struggles to drop out of suspension or the oats and wheat currently going into IPAs and other styles. And you have all the reason behind the hazy beer that is currently coming out of modern breweries.

Different styles of beer


While it can be bought from yeast suppliers it’s the most famous as the major flavor component in lambic. The beer inoculated not from a packet but from the air in and around Brussels and the wooden barrels it’s fermented in. Because it’s often found in spontaneous beers it’s usually in conjunction with other wild bacteria.

With its influence throughout the entire brewing and tasting experience, it’s no wonder yeast is seeing a lot of research and development recently. And laboratories are constantly innovating to make both the brewer’s life easier and to widen their palate.

So next time you crack a beer have a think about how much its character might be coming from the choice of yeast. You’ll find there isn’t one part of the beer structure that is not influenced by it. Aroma, flavor, sweetness, body, even shelf life. So as drinkers we can get a much better understanding of beer by knowing the process yeast goes through and the varieties available. Whatever the style, the success of the beer all comes down to what that tiny microbe does in secret behind those wooden or stainless walls. Cheers.

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