Understanding Yeast: Pitching and Fermentation

Yeast is a crucial component in the brewing process. It's responsible for converting the sugars in the malt into alcohol and carbon dioxide, a process known as fermentation. This unit will delve into the role of yeast in brewing, how to prepare and add yeast to your brew (a process known as pitching), and what happens during fermentation.

Understanding Yeast

Yeast is a type of fungus that consumes sugar and produces alcohol, carbon dioxide, and various flavor compounds. There are many different strains of yeast, each with its own characteristics and flavor profiles. In brewing, we primarily use two types of yeast: ale yeast (Saccharomyces cerevisiae) and lager yeast (Saccharomyces pastorianus). Ale yeast ferments at warmer temperatures and typically produces beers with a wide range of flavors and aromas. Lager yeast, on the other hand, ferments at cooler temperatures and produces beers with clean, crisp flavors.

Yeast Propagation and Pitching

Before yeast can be added to the wort (the sweet liquid extracted from malted grains), it needs to be activated in a process known as propagation. This involves rehydrating dry yeast or activating liquid yeast in a small amount of warm water or wort. Once the yeast is active, it's ready to be pitched into the wort.

Pitching yeast is simply the process of adding yeast to the wort. The amount of yeast you pitch can have a significant impact on the final beer. Too little yeast can result in a slow or stuck fermentation, while too much yeast can lead to off-flavors. As a general rule, you should aim to pitch around 0.75 to 1.0 grams of yeast per liter of wort for ales, and 1.5 to 2.0 grams per liter for lagers.

The Fermentation Process

Once the yeast is pitched, it begins to consume the sugars in the wort. This process produces alcohol, carbon dioxide, and heat. The yeast also produces various flavor and aroma compounds that contribute to the character of the beer.

Fermentation typically takes one to two weeks, depending on the yeast strain, fermentation temperature, and the original gravity of the wort. During this time, it's important to maintain a stable temperature and protect the fermenting beer from light and oxygen.

In the next unit, we'll explore the different types of fermentation and how they can impact the final beer. But for now, remember that yeast is a vital part of the brewing process, and understanding how to properly propagate and pitch your yeast can greatly improve the quality of your homebrew.