Boiling is the third step in the process of brewing ale. The wort that is collected after lautering is transferred to a kettle that is usually made of copper. Heat is then applied to cause the wort to come to a rolling boil. This is different from other types of boiling such as simmering in that the bubbles are large and numerous at the bottom of the kettle. However, it is also important to make sure that even though it is a violent boiling, it should not be strong enough to evaporate about 5% of the liquid within one hour. A rolling boil results in the development of a stable beer.
Another reason why the boiling has to be rolling is the driving out of the oxygen from the wort. Oxygen has to be liberated because it causes much darker coloration that what may be desired and it also promotes infection. A third reason for a rolling boil is the breakdown of proteins.
Boiling causes many important biochemical processes to occur in the kettle. First, it offers sterilization. Second, it kills off the enzymes, which should not be there once fermentation begins. Others include:
* Protein precipitation- boiling helps coagulate unstable proteins. * Development of color * Concentration * Oxidation
By the application of heat, the wort is stabilized. This causes a decrease in the wort pH thus providing a suitable environment for hops processing. Hops are the flower of the Humulus lupulus plant and are used in beer preparation because they bring flavor and stability to the wort. Hops bring a dash of bitterness to balance out the sweetness of the wort. They produce the flowery and fruity aromas of the ale. Lastly, hops have an antibiotic effect that selectively ensures the activity of the yeast that is added later over other less desirable organisms. The addition of hops to the wort should follow a strict schedule conscientiously.
Furthermore, boiling also volatilizes any harsh unpleasant odors from the malt. It also produces color and flavor from the wart sugars themselves.
Boiliing typically lasts for 90 minutes. The first five minutes are required to accomplish sterilization, while an additional ten minutes allows for enzyme destruction. An additional fifteen minutes is required to eliminate tannins from the grain husks, which would otherwise produce an astringent taste in the wort. With the first 30 minutes over, the rest of the time is devoted to the strict hop schedule.
Once this is done, the wort is now ready for the next step which is fermentation.