White Labs once made two beers with the same wort and the same yeast—the same everything, in fact, except the temperature of the fermentation. The beers tasted completely different. The beer fermented at 66°F registered a scant 7.98 parts per million of acetaldehyde, which usually has a sort of green-apple taste, but that’s below most people’s threshold for being able to taste it at all. The one brewed at 75°, meanwhile, had a whopping 152.19 parts per million.
