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What Is Brewer’s Yeast?

WRITTEN ON 16 December, 2021

Brewer’s yeast is a single-cell fungus used in making all types of alcoholic beverages.

Brewer’s yeast plays a key role in beer fermentation — essentially consuming the sugars obtained from malted grains like barley and wheat, and producing alcohol and carbon dioxide. Brewer’s yeast also produces other compounds like esters and phenols during fermentation that contribute to taste, aroma and flavour in beer.

The production of quality beer with varied flavour profiles relies on the type of yeast strains used in the brewing process and its fermentation activity.

There is one particular brewer’s yeast genus — Saccharomyces (scientific name) often used in the brewing industry. Saccharomyces can be divided into two categories:

1. Lager Yeast

Lager yeast, Saccharomyces pastorianus, is used to make lager beers. These yeast cells sink below the fermenting liquid to carry out fermentation, hence called bottom-fermenting yeast.

Lager yeast functions effectively at cooler temperatures, 5℃ – 10℃ (41℉ – 50℉). They have special genomes to ferment more sugars than ale yeast, in turn, producing a light and crisp taste in lagers.

2. Ale Yeast

Ale beers are fermented with Ale yeast, Saccharomyces cerevisiae. Also known as the top-fermenting yeast, they work effectively at the top of the fermenting liquid.

As temperature affects the yeast fermentation process, ale yeasts function best at warmer temperatures from 15℃ – 24℃ (60℉ – 75℉). Characteristically, these yeast strains produce more esters at warmer temperatures, leading to fruity flavours in ale beers.

The Use Of Non-Saccharomyces Yeasts In Brewing

Besides the most common use of Saccharomyces yeasts in beer production, craft brewers are using non-Saccharomyces yeasts to produce low-alcohol beer, and probiotic beer and obtain desired sensory profiles in beers. Non-Saccharomyces yeasts have greater metabolic and enzymatic capacities that contribute to distinct flavour and aroma.