Top-fermented yeast and bottom-fermented yeast are two different types of yeast used in the beer brewing process. The main difference between the two lies in the temperature at which fermentation takes place and the flavors that are produced as a result.
Top-fermented yeast, also known as ale yeast, is typically used in the production of ales and other top-fermented beers. It works at warmer temperatures, usually between 15-24°C (59-75°F). During fermentation, the yeast rises to the top of the fermentation vessel, hence the name “top-fermented.” This type of fermentation is more traditional and has been used for centuries.
One of the key characteristics of top-fermented yeast is that it produces more esters, which are flavor compounds that give beer fruity and spicy notes. These esters are more pronounced due to the warmer fermentation temperatures. For example, a Belgian ale brewed with top-fermented yeast may have fruity flavors like banana or apple, and spicy notes like clove or pepper. These flavors contribute to the complexity and depth of the beer.
In addition to esters, top-fermented yeast also produces phenols, which are aromatic compounds that can contribute to flavors such as tannin or smokiness. These phenols can add another layer of complexity to the beer, depending on the specific strain of yeast used.
On the other hand, bottom-fermented yeast, also known as lager yeast, is used in the production of lagers and other bottom-fermented beers. It works at much lower temperatures, typically between 7-13°C (45-55°F). During fermentation, the yeast settles at the bottom of the fermentation vessel, hence the name “bottom-fermented.” This type of fermentation is a more modern technique that was developed in the 19th century.
The main difference in flavors produced by bottom-fermented yeast is the absence of pronounced esters. The lower fermentation temperatures suppress the production of esters, resulting in a cleaner and crisper taste profile. Lagers brewed with bottom-fermented yeast tend to have a more subtle and delicate flavor profile compared to ales. They often exhibit a smooth and well-balanced character.
Furthermore, bottom-fermented yeast produces fewer phenols compared to top-fermented yeast. This results in a beer with less tannin or smoky flavors. Instead, lagers focus more on malt and hop flavors, showcasing the ingredients used in the brewing process.
The main difference between top-fermented yeast and bottom-fermented yeast lies in the fermentation temperature and the flavors produced. Top-fermented yeast, used in ales, works at warmer temperatures and produces more esters and phenols, resulting in a beer with fruity, spicy, and sometimes smoky flavors. Bottom-fermented yeast, used in lagers, works at lower temperatures and produces fewer esters and phenols, resulting in a cleaner and crisper beer with a focus on malt and hop flavors.