Explaining the Beer Fermentation Brewing Processes
Initially, the process seems quite simple. Yeast is added to your cooled wort, and it starts consuming oxygen and nutrients, multiplying in the process. They will keep multiplying until all the oxygen is used up. Then, they attack the sugars in the beer as if it’s their last meal. The fermentation can be so vigorous that a foamy head can rise a foot or more above the top of the beer, accompanied by the production of significant amounts of CO2.
During yeast fermentation, alcohol, CO2, and other byproducts such as fusel alcohols (or fusel oils) are produced. Fusel oils consist of a mixture of organic acids, higher alcohols (propyl, butyl, and amyl), aldehydes, and esters, known collectively as congeners. It is these congeners that are believed to be responsible for causing hangovers.
This process continues until all the simple sugars in the beer are consumed. The yeast then start to settle down. Some become dormant and sink to the bottom, while others continue consuming the more complex sugars and other byproducts in the beer. Eventually, when there is no more food left, the yeast settle at the bottom of the fermenter and wait for more nourishment.
Comparison of Beer Fermentation: Lagers vs. Ales
Typically, this beer fermentation process takes about a week for most beers. Higher fermentation temperatures result in the formation of more byproducts (ranging from fruity esters to solvent-like fusel alcohols), giving the beer a fruity or phenolic flavor and aroma. On the other hand, at cooler temperatures, the yeast work slower, and the production of byproducts is minimal. This is one of the main differences between lagers (fermented at low temperatures) and ales (fermented at higher temperatures).
Lagers have a cleaner taste compared to ales, with flavors that are more inclined towards malt and hops. Ales, on the contrary, have more complex aromas and flavors, leaning towards fruity and spicy characteristics. However, there is a somewhat linear relationship with temperature. Ales fermented at colder temperatures will exhibit less “ale character” and more “lager character.” Conversely, lagers fermented at warmer temperatures will show more of the “ale character,” with increased production of fruity/spicy esters.
The other difference, which usually distinguishes the two types of yeast, is the location of fermentation. Lager yeasts ferment at or near the bottom of the beer, while ale yeasts ferment at the top before settling. Considering that yeasts are omnipresent, it makes sense that some strains would be adapted to colder climates. This is how they were discovered. Beer fermented in colder climates, such as Germany, was stored in ice caves to prevent spoilage during the hot summer months. Normal ale yeast wouldn’t be capable of efficiently cleaning up the byproducts of primary fermentation in such a cold environment. The strains of yeast present in the German region during winter were already adapted to cold beer fermentations through evolution. Once the nature of yeast was understood, it became evident that this was a distinct type of yeast from the ale yeasts used until then. The term “lager” originated from the practice of storing beer in caves, as “lager” means “to store” in German.