For every beer brewed, the yeast cells live out a whole series of steps. They wake up, grow new yeast cells, consume sugars, and produce carbon dioxide, alcohol, and a host of other compounds, then drop back into a dormant state and fall out of solution. It’s easy to overstate the extent to which we as brewers actually “make” beer and just as easy to understate the extent to which yeast cells are doing the bulk of the hard work. Yeast, though, works in an environment that we manipulate, and the ways in which we tinker with that environment greatly impact the work that yeast can do within it. One of the key features of that environment is temperature, and good brewers manage temperatures to give their yeast the best shot at producing the beer that the brewers (and, I think, the yeast) really want.
We could talk for days about ideal fermentation temperatures for different yeast strains, but we’re going to keep it simpler than that. We’re just talking about ways to manage temperature, whatever you want that temperature to be. Control is the name of the game for many aspects of brewing, and controlling temperature should be first on your list as a brewer because your yeast’s health, performance, and effectiveness are relying on it. Yeast cells want a steady and productive environment, and that’s just what we should endeavor to give them.
I’m sure that most of you already have a good sense of why temperature management matters in brewing. Yeast will produce different precursors and compounds, consume sugars at different rates, yield different flavor profiles, exhibit symptoms of stress, and attenuate more or less completely depending on the temperatures in the beer as it is fermenting. Temperature will affect how quickly fermentation starts, how long it lasts, and what is left behind. Temperature will increase the risk of off-flavors, decrease the development of esters and phenols, and often will mean the difference between sweet, apple-like ethanol and harsh, hot fusel alcohols. Neglecting the temperature of your fermentation makes about as much sense as not tuning your guitar before a performance. Temperature matters. I’d go so far as to say that nothing matters more than temperature. So, if everyone is sufficiently panicked, let’s get into how you keep it under control!