STAGES AND LENGTH OF BOILING
From practical point of view, boiling should not take less than 90 minutes. The specific length depends on the hop schedule. The minimum time is explained by the following. Sterilization requires about 5 minutes. An additional 10 minutes (total of 15 minutes) will kill the enzymes. Another 15 minutes are needed to eliminate tannin originating from malt husks. This first half hour, in case of infusion mash, is to decompose and precipitate some of the proteins. This should be accomplished before hops are added, because otherwise the sticky hop resins will combine with the coarse protein flocks and precipitate out of solution. When decoction mashing is used, excessive complex proteins are usually not a problem. After that, calculate the total time needed to evaporate the desired amount of wort. Subtract the above 30 minutes. The remaining time should include the hops schedule so that the hops should not be boiled longer than one hour. Except for high gravity beers, the total boiling time should not last longer than 2 hours. Boiling the hops longer than one hour will start generating sharp, undesirable and unpleasant flavors. During a long boil a greater percentage of the hops bittering and preservative qualities are carried into the finished beer.
Thus, the stages of boiling are characterized by the functions: sterilization, driving out oxygen, killing enzymes, protein break-down, evaporation of water and hops processing.
