Bottom fermentation gets its name from the traditional German brewing process used to create certain types of beer. In this process, a specific type of yeast is used that tends to sink to the bottom of the brewing vessel during fermentation. This is in contrast to other types of yeast used in brewing, which tend to rise to the top or float on the surface.
The term “bottom fermentation” is used to describe this specific type of yeast behavior during fermentation. It is called so because the yeast settles at the bottom of the vessel, creating a distinct layer.
To understand why bottom fermentation occurs, let's delve into the science behind the process. During fermentation, yeast consumes the sugars in the wort (the liquid extracted from malted grains) and converts them into alcohol and carbon dioxide. Different strains of yeast have different characteristics and behaviors during this process.
Bottom-fermenting yeast, scientifically known as Saccharomyces pastorianus, has adapted to work at cooler temperatures, typically around 7-13°C (45-55°F). At these temperatures, the yeast cells tend to be less active and settle to the bottom of the vessel. This behavior is advantageous for several reasons.
Firstly, bottom fermentation allows for a cleaner and clearer beer. As the yeast settles at the bottom, it takes with it various by-products of fermentation, such as proteins, hop residues, and other solids. This helps to clarify the beer, resulting in a smoother and visually appealing final product.
Secondly, the cooler fermentation temperatures used in bottom fermentation help to promote the production of certain flavor compounds. These compounds contribute to the characteristic profile of bottom-fermented beers, which are often described as having a clean, crisp, and sometimes slightly fruity taste. The lower fermentation temperatures also result in slower fermentation, allowing for a more controlled and gradual production of flavors.
It is worth noting that bottom fermentation is not limited to just German beers. The process has been widely adopted and used in the production of lagers around the world. Lagers are a type of beer characterized by their bottom-fermentation process and are known for their smooth and refreshing qualities.
In my own experience as a brewer, I have found bottom fermentation to be a fascinating process. The meticulous temperature control and the careful selection of yeast strains are crucial in achieving the desired flavors and characteristics. It requires patience and attention to detail, but the end result can be incredibly rewarding.
To summarize, bottom fermentation is called so because the yeast used in this process tends to settle at the bottom of the brewing vessel during fermentation. This behavior is due to the specific characteristics of the yeast strain used, which adapts to cooler temperatures and results in a cleaner, clearer beer with distinct flavor profiles.