The sweet liquid is pumped very slowly to the kettle from the mash tun, where the remaining sugars have been rinsed ("sparged") from the grain bed with hot water. Boiling the resulting liquid ("sweet liquor") adds further Melanoidin coloring, serves to sterilize and clarify the finished product, and initiates the precipitation and removal of unwanted molecular proteins.
When crafting fruit ales, ingredients such as raspberries, marionberries or boysenberries may also be added late in the boil.
There are many important attributes associated with the boil. This is where the hops and fruit are added to flavor the beer. The most important part of the boil is the sanitizing effect it has on the wort. By boiling for ninety minutes spoilage bacteria does not have much of a chance of surviving to taint your finished product. This ninety minute boil will also drive off some undesirable by products of the mash (dimethylsulfide DMS) and purge all of the oxygen out of the wort. Also, the pH of the wort (acidic) in conjunction with the physical kinetic motion of the boil forces proteins that were previously soluble to come out of solution. These pieces will then combine to form big protein formations. Brewers refer to this action as the “hot break”. These proteins are then big enough to be screened out of the wort as it is pumped to the fermenter. This is convenient because excess protein can negatively affect the flavor, appearance and stability of the finished beer.
