Watch that Temper(ature)! March 29, 2016 08:00 2 Comments
“Now don't be sad, 'cause two out of three ain't bad.”
- Meatloaf & Jim Steinman
When it comes to fermentation, whether it is beer, wine, cider, sauerkraut, or whatever, there is a long list of things you should do, and a very short list of things you have to do – a holy trinity of sorts. 1. Sanitize. SANITIZE. 2. Use quality ingredients. (As a corollary – use the right equipment.) 3. Control your fermentation temperature. Hot break, cold break, water chemistry, alpha acids, pitch rates, etc.: these things are all important and will all make a difference in the quality of your brews. But on their own each won’t generally ruin your final product. On the other hand, not sanitizing, using low quality ingredients or the wrong equipment, and fermenting too hot or cold can ruin your fermentation pretty easily.
Of these three, the most difficult is temperature control. (The first two are easy: just shop at Central Street Farmhouse.) The appropriate temperature for your fermentation will vary from style to style and among the various fermented foods or beverages. Someday I may tackle sauerkraut or kefir here, but for now let’s make a few notes about wine and then focus on beer. As a general rule, wine prefers warmer temperatures. Anything from 60 – 85 degrees is fine – for red wines, ferment hotter (over 70) and for white wines, a little cooler (under 70). Red wines can benefit from tannin extraction at the higher temperatures, and white wine will lose less of its complex aromatics when kept a bit cooler. Depending on the yeast chosen, mead should follow the guidelines for white wine, and wine made from fruit will vary with the yeast selected and the type of fruit.
Everyone knows there are two basic categories into which all beers fit: lagers and ales. Technically speaking, it is not so straightforward, but for our purposes these categories work. Lagers are fermented at cooler temperatures – primary in the low 50s and then lager in the 40s or even lower. If you get too cold, you will make an ice beer. Most lager yeasts benefit greatly from a diacetyl rest after primary. At this time, bring your fermenter back up to room temperature to help the yeast clean up the butterscotch flavor caused by diacetyl. This is a normal by-product, and is acceptable in some styles at low levels, but can be off-putting. The cool temperature of lagering slows yeast’s ability to get rid of diacetyl, but a brief warming period takes care of the problem. The cool fermentation temperatures serve several purposes: limiting esters in primary, extended conditioning phase to clean up residual sugars and off-flavors, and clarity. Lager yeasts have been bred to work in the cold and react differently to sitting at 45 degrees than ale yeasts.
The other category - ales - is by far the most common type of beer. Within this broad category are too many styles to address individually, but the side effects of fermenting too warm or cool are basically the same for each. (The primary exception here is most Belgian styles, but even they can be fermented too warm or cold.) For the most part, ales want to ferment in the 65 to 68 degree range. As with lagers, fermenting too hot will produce esters. In some styles, these can be a desirable fruity element to a point. Fermentation at high temperatures will generally result in overdone esters, or a green apple flavor (from acetaldehyde) and/or alcohol flavor (from sharp and unpleasant-tasting fusel alcohols). High temperatures are not the only cause of cidery beer or booziness, but they are often the cause when these flavors are unpleasant. Fermenting below 65 will cause slower fermentation, and potentially stall fermentation completely when dipping below 60.
In any case, yeast first adapts to the wort or must (depending what you are fermenting) when you pitch the yeast and then has to deal with the temperature of the wort or must going forward. Pitching temperature needs to be low enough such that the yeast is not killed. We always say below 100, but ideally pitch when your wort is the temperature at which you will ferment. (Lagers can start in the 60s and cool down as fermentation begins.) An extreme temperature change when the yeast is getting started can cause stress, which will cause other off-flavors or put a halt in your fermentation. Many brewers prefer to start fermentation on the cool side of the ideal range and slowly raise the temperature to make sure fermentation is complete. Changes are fine, as long as they are gradual and minimal.
The other side of temperature control is consistency. The thermal mass of five gallons of fermenting beer is resistant to a certain degree of temperature swings. A change of 62 to 68 degrees in your house or apartment when you go to work and return home will not make a huge difference in the final product. However, being too close to a wood stove can cause twofold problems. For one, it will get too hot when the stove is going. And two, if you are like me, when the fire goes out overnight, the house gets significantly colder and the fermenter will cool off. (This is, of course, why I do not practice or recommend placing fermenters next to wood stoves.) The jury is still out on how much of a difference this temperature change will make, but it is still best to minimize these swings.
All of this information is great, but how does the average homebrewer apply said knowledge? First, brew seasonally. Don’t try to lager in the summer if you don’t have a fridge. Don’t make a Belgian-style wit or a hefeweizen in the winter and expect it to have the same flavor as it did in the summer. Second, find a spot you can control. An unfinished basement - or otherwise unheated room that stays above freezing - is a good place to lager in the winter or minimize esters in the warm months. Or maybe that spare bedroom with electric heat can be used for fermentation when it gets cold. Set the thermostat at 65 and have at it! Third, get the right equipment. No, not that glycol system you heard about on a brewery tour, but yes to that Brew Belt, Cool Brew, or repurposed dorm fridge sitting in the garage. You might even need to spring for a thermostat override for a chest freezer, but trust us, it will be worth it!
There it is, the most challenging piece of the holy trinity. They are all equally important: sanitize, use the right ingredients, and control your temperature! While two out of three ain’t bad, Mr. Loaf, it certainly ain’t good, either.