A Guide to Beer Yeast Types and How They Shape the Flavor of Your Brew

Yeast is the amazing little microbe that is responsible for fermentation. Ancient brewers would give thanks to the gods for fermentation as their sweet liquids would turn into intoxicating beverages via naturally occurring yeasts. As science has evolved and microbiology has been embraced by professional brewers, yeasts have been classified, tamed, and used to create wonderful flavors and aromas in beers. 

In case you need a simplified recap of the brewing process: a beer starts out when grains are boiled. The resulting sweet liquid, known as wort, is then dosed with hops or other adjuncts and cooled. It’s then transferred to a fermentation vessel where yeast is added, or “pitched” in brewing terms. The yeast consumes the sugars in the wort and converts them to alcohol and carbon dioxide. 

By employing various yeast strains, it’s possible to achieve aromas of bubblegum, banana, clove, pepper, honey, flower, fruits, and more just from the microbe. 

Understanding yeast

Lagers are fermented by yeast (Saccharomyces pastorianus, also known as Saccharomyces carlsbergensis) that operate better at cooler temperatures. 

These beers need to be conditioned or cellared (“lager” is German for a storage place) for several weeks or more to reach peak drinkability. Lagers are the traditional beers of the Czech Republic, Germany, central Europe, and the dominant style in the United States.

Beers like Bud Light, Michelob Ultra, Heineken, Coors Banquet, Miller High Life, and even Pabst Blue Ribbon are all commercial examples of lagers. They are difficult to make well and require proper brewing equipment as well as patience, technique, and historical knowledge. 

Ales are produced by yeast (Saccharomyces cerevisiae) that operate better at warmer temperatures during fermentation. Ales can be ready to package and drink in a matter of days rather than weeks, and the yeasts produce extra flavors in addition to creating alcohol. These can be fruity, spicy, or earthy. 

Ales are often considered the traditional beers of England (porter, stout, pale ale, bitter) and of Belgium (saison, gueuze) and have fueled the modern beer renaissance in America via the India pale ale (IPA). 

Wild Yeast

Wild is a word that gets tossed around quite a bit in the beer space when it comes to fermentation. 

Indeed, yeast is naturally occurring all around us and when the right microbes land in sweet, exposed, liquid fermentation can occur. In the grand scheme of beer, however, there are not too many true examples of wild yeast fermentation. 

There are some spontaneous fermented beers, like lambic, that are the result of exposing cooling wort to the elements, allowing wild yeasts and beer-friendly bacteria to inoculate the beer. These beers are made in a vessel called a coolship, which is a large, shallow stainless-steel container that allows for a large surface area of the liquid to be exposed to air and natural microbes. Most breweries with a coolship use them between late fall and early spring. 

The most common and likely best-known wild yeast strain is Brettanomyces, often referred to in shorthand as Brett, which is also employed in certain styles of winemaking. Often brewers will describe the flavors and aromas of Brettanomyces as “barnyard” or “horse blanket” which can be accurate, but also does the yeast strain a disservice. Yes, it is funky and can be earthy and a touch pungent, but when used properly and allowed to express itself, it brings aromas of leather, and spice, tobacco, and pepper to the forefront.

A lot of Brettanomyces used by brewers these days have been cultivated in labs and are used by breweries to create beers without the use of a coolship. 

Since yeast is naturally occurring around us, one yeast cultivation lab, Bootleg Biology in Tennessee has created a project that aims to gather a native yeast sample from every zip code in America to bring a true sense and taste of place to a beer. 

There’s also been a rise in the number of house cultures that brewers use to create beers, with the goal of crafting unique signature profiles. 

Brewers cultivate house cultures and often pull together different yeast strains that work in tandem with each other to create flavors and aromas that cannot be found elsewhere. 

Kveik (pronounced kwike) means yeast in the Nordic regions where it is found. After years in obscurity outside of its home region, it has become a popular option among brewers around the world. This is due to not only the fruity flavors it can give to a beer but also how quickly it can fully ferment a beer, often within days. 

Another yeast-related term that beer drinkers are likely to encounter is “secondary fermentation.” This is when brewers add a small dose of yeast to a bottle of beer just before it is capped and sent off to be sold. The new yeast consumes any residual sugars in the fermented beer, creates extra complexity and offering a pop more of carbonation. Homebrewers are well-known for removing the yeast dregs from these bottles to create their own recipes on a small scale.

Though a handful of common yeast strains may create the base of most commercial beer, nearly any type of yeast can be experimented with, and many producers embrace these opportunities to get weird. While some may choose to harvest and cultivate yeast strains from unconventional locals, often to recreate historic styles of ancient ales, others have sourced yeast from places as unlikely as the belly of a wasp, or from the beard of long-time brewer. It goes to show, if something can be used for fermentation, there's a brewer that's bound to try.