Yeast plays a central role in beer brewing as the microorganism responsible for fermentation. During the brewing process, yeast consumes the sugars extracted from malted grains and converts them into alcohol and carbon dioxide, creating beer’s characteristic flavour, aroma, and effervescence. There are two primary types of yeast used in brewing: Saccharomyces cerevisiae, which is commonly used for ales, and Saccharomyces pastorianus, used for lagers. Each type imparts distinct characteristics to the beer. For example, ale yeast ferments at warmer temperatures and produces fruity and spicy flavour notes, while lager yeast ferments at cooler temperatures, resulting in a cleaner, crisper taste. The choice of yeast strain is critical, as it influences not only the alcohol content but also the subtle complexities of the final product.
Beyond fermentation, yeast contributes to the beer’s overall quality and stability. During fermentation, yeast produces secondary compounds like esters and phenols that enhance the beer’s aroma and taste. Brewers can manipulate factors such as fermentation temperature, oxygen levels, and yeast pitching rates to control these flavours. Additionally, yeast helps to clarify the beer by flocculating, or clumping together, which allows the solids to settle at the bottom of the fermentation vessel. After fermentation is complete, the yeast can often be reused for future batches, making it an economically valuable component of the brewing process. The symbiotic relationship between brewers and yeast underscores its indispensable role in transforming a basic mixture of water, malt, and hops into the diverse and dynamic world of beer.