Boil

The obvious definition is bringing a liquid to a high enough temperature that it begins to bubble and evaporate. For pure water at sea level, this occurs at 212° F (100° C). Boiling occurs at lower temperatures at lower pressure, so at higher elevation, boiling requires the addition of less heat. Boiling serves a few purposes when making beer. Preeminent is the isomerization of the alpha and beta bittering acids from hops making them water-soluble Boiling is also important for precipitating certain undesirable proteins from the grain solution; the hot break occurs during first five or ten minutes of a boil, and the cold break occurs while rapidly cooling the boiled sterilizing wort mixture.