I know I’m skipping around a little bit (after all, there are several steps that come before fermentation in the brewing process), but it’s kind of because fermentation is my favorite. After all, it’s responsible for some of the best-tasting things in life: beer, wine, cheese, and chocolate to name a few. It’s a crucial step, chemically, as it creates the alcohol that we all enjoy (presumably you enjoy alcohol – you are on a beer blog).
Photo from uncommoncaribbean.com
Fermentation, at its very simplest, is the chemical process by which yeast converts the malts‘ sugar (glucose) into ethyl alcohol and C02 gas – this yields both the alcohol content and the carbonation that make beer, well, beer.
We’ve explained a little bit that temperature is important for this process, depending on the kind of yeast being used and the beer style that is being made – an ale needs to be kept at 68 degrees Fahrenheit for about two weeks and a lager needs to stay at 48 Fahrenheit for about six weeks. This process creates a lot of heat as a byproduct and so the container in which the fermentation happens generally needs to be carefully cooled.
To avoid contamination by stray, wild yeasts, fermentation tanks are generally sealed off from the air with only a small vent for the CO2 buildup to exit the tank.
I’m no chemist, so I’m not going to go into that level of detail! However, there are some interesting things that go on during the fermentation process that need to be addressed. Yeast basically works in two stages during fermentation: the primary stage and the anaerobic phase.
In the primary stage, the yeast consumes all of the oxygen in the cooled and aerated wort mixture. During this stage, sterols (which are a type of cholesterol that make up part of the yeast’s cell wall) are produced. These sterols allow the cell wall to be permeable so sugar and alcohol can move in and out of the yeast cells; they also allow the yeast to survive in an increasingly alcoholic environment
Once that oxygen is gone, the yeast moves into the anaerobic phase, during which most of the sugars in the wort are turned into ethanol and CO2. Additionally, flavor compounds like esters (fruity notes) , diacetyl/ketones (butterscotch notes), fusel alcohols (responsible for a hot or burning sensation), and other chemicals that can make or break the flavor of a final beer.
Other Uses for Fermentation
Cacao seeds must be fermented (often out in the sun, on large tarps) before being dried and then roasted in order to create the chocolate flavor that we know.
In winemaking, fermentation begins naturally when the skin of grapes is broken and the wild yeast on them and in the air begin the primary fermentation stage, turning sugar in to alcohol.
Fermentation happens several times along the journey from milk to cheese, developing flavors and even creating the famous holes in Swiss cheese.
The workhhorse of bread making, yeast-based fermentation creates the textures, flavors, and rise in bread doughs.
Pickles, sauerkraut, kimchee, and more can be fermented during the pickling process, allowing natural bacteria to create acids needed to preserve foods.