Does it matter at what temperature your beer ferments? If you’ve looked around at recipes you will have read all kinds of very specific directions about temperatures and sometimes it seems pretty arbitrary. Nobody explains why or how. This will be a two-part posting about what this is all about, today, and then tomorrow we’ll talk about what to do if you’re not lucky enough to have a climate-controlled fermentation setup. We don’t! You don’t need fancy stuff to brew great beer. That’s what we’re here for.
Remember that people have brewed outstanding beer for centuries before electricity was discovered. This is low-tech stuff.
The answer to the first question above is: yes, it can. It totally depends on the yeast you’re using and the desired flavor for your beer. When you dump a packet of yeast into a freshly brewed batch, what happens is a chemical process undertaken by the digestive system of yeast. These are very simple single-cell organisms and they are profoundly affected by their environment.
We do the first step for them by giving them the right ingredients to work on. But getting the temperature right helps the yeast be more efficient and, sometimes, less efficient with certain chemical reactions that take place. What happens for one yeast cell is not very important, but when you magnify it by the huge number of yeast we’re growing in a batch of beer, it matters. This is, after all, where most of transformation from sugar water to beer happens.
There are two general families of beer yeast. Ale yeast and lager yeast. There are other distinctions between the two, but here we’ll concentrate on temperature ranges. Ale yeasts are happiest at about 60-75 degrees Fahrenheit (18-24 Celsius) while lagers yeasts are happiest at about 50-60 degrees Fahrenheit (10-18 Celsius).
So that’s great, but how do you know what to do for your particular beer? Many recipes don’t tell you. The yeast producers step in to fill the void. Good businesses like Wyeast and White Labs give you information on their websites. Here is an example. Let’s say we’re brewing a stout and we want to use Wyeast’s Irish Ale Yeast to do it. We hop onto their web site and look it up. If you click on that link you’ll see that Wyeast says this about the yeast:
Beers fermented in the lower temperature range produce dry and crisp beers to fruity beers with nice complexity in the upper range. Ester production is enhanced with fermentation temperatures above 64 degrees F (18 C).
This looks like speaking in tongues to the uninitiated, but what’s it’s telling you is that the yeast ferments well over a range of temperatures, giving you an idea of what to expect from the yeast in the different temperature ranges.
In plain English what this says is that fruitier tasting beers (think banana-like smells) are fermented by this yeast at higher temperatures. At lower temperatures you get a nice, dry, crisp beer. Esters produced by the yeast are what affects this fruitiness. So the 64 degrees marker shown in this spec means that if you want a fruity taste in your stout, aim for a temperature above this. If not, aim low. Generally for a stout, as opposed to some other dark beers, you don’t want a fruity taste.
So in this case we now know we ought to ferment below 64 degrees (probably around 60-62 degrees) for our most desired taste.
Tomorrow: how do I control the temperature?