Boiling is an important part of the beer-making process. It accomplishes several main tasks:
- Sanitizes the wort.
- Extracts bitterness, flavor and aroma from the hops.
- Denatures any remaining enzymes from the mash, fixing the proportions of wort sugars.
- Concentrates the wort by boiling off water.
- Allows for coagulation and removal of excess (often undesirable) protein and polyphenol compounds from the wort.
- Drives off S-Methyl Methionine (SMM), a natural component of malt, which is the precursor to Dimethyl Sulfide (DMS), a sulfur compound produced during fermentation of beer that has the aroma of cooked or creamed corn.
Hops added at different points provide different qualities:
Adding hops early in the boil (typically 60 to 90 minutes before flame-out) extracts bitterness from the hops by isomerizing certain hop resins (mostly alpha-acids).
Adding hops later in the boil (typically 15 or less minutes left) extract flavors from the hops.
Adding hops extremely late in the boil (typically with 5 or less minutes left) extracts hop aromas.