Well it’s certainly getting colder out. Today was evidence of that. And yes, walking around in a light jacket may feel nice, but I’m excited for the cold for other reasons. For the first time in a looong time, I see my fermentors’ temperatures are down in the 60’s. Very exciting!
Why?
In short, cooler temperatures will mean better beer. If you’re a close follower of the Zeptobrewery, you’ll notice that Spring and Summer ’10 saw record beer production as well as record temperatures. Most of the beer was fermenting around 76 degrees Fahrenheit. Sometimes higher. For most yeasts, 75 is the highest you should feel comfortable fermenting at. When the fermentation gets too hot, you get what is described as ‘off flavors.’ Maybe you’ll like the flavors, but chances are they weren’t desired. Phenols and esters in particular are affected more at higher temperatures, and while some of these flavors and aromas are certainly desirable, they can be acquired at lower temperatures, in more desirable amounts. While plummy, raisin flavors can be good in darker beers, they should not dominate the palate.
Furthermore, beer fermented at hotter temperatures will actually taste hot. Higher alcohols are produced and some ‘nail polish remover’ flavors may come through. For a beer with 12% ABV, that’s not as big a deal. But for a session ale, or simply a lighter beer, with say 4.8% ABV, the taste of higher alcohols is misleading as to its alcohol content as well as being not entirely pleasant.
It’s also very difficult to do a diacetyl rest of my fermentor at 68 degrees for three days when the ambient temperature is in the mid-70’s. What I can do now is use either a heating belt or heating pad under the fermentor (to keep a yeast-healthy temperature of under 75) and then remove the heat to crash it to whatever cool ambient temperature (as long as it’s under 68, I’ll be happy). Many say diacetyl rest is only needed for lagers because diacetyl clears up at 68 and above, but if nothing else, many brewers agree it’s a good thing to start at a higher temperature of fermentation and have it decline (example: 72-68). Plus I will be able to feel confident that beer I’m storing in bottles will not age poorly at high temps – but I have to make sure it’s not too cold or the carbonation may be affected.
The last thing I’m happy about the cold? Cold break! While it may take me slightly longer to heat up my brew water, it should take me significantly less time to cool it! This will be for three reasons. One, I will be getting a new 50-foot stainless steel wort chiller to replace my 20-foot copper one. And two, the water from the sink will start out much colder than it did during the summer. And third, the ambient temperature will be lower, allowing a better play of thermal mass. A faster chilling of the wort to temperatures where I can safely pitch the yeast will result in less cloudy beer and a cleaner, smoother flavor.
Also getting excited for those winter beers – one of my four favorite beer drinking seasons.
The Bongo Zeptobrewery 