Kettle Boil

After the hops are added to the wort, the mixture is boiled for one to one-and-a-half hours. Boiling accomplishes at least seven functions. First, it kills nearly all of the microorganisms remaining after mashing, making the wort, for all practical purposes, sterile. Second, boiling inactivates most of the enzymes still active after mashing or reduces their activity to barely detectable levels.Third, the boiling step enhances extraction of oils and resins from the hops and accelerates isomerization of hop acids. Fourth, proteins, tannins, and other materials that would ordinarily cause clarity and cloudiness problems precipitate during the boiling step. Removing this precipitate (known as "hot break" or "hot trub") helps to prevent such defects. Fifth, wort boiling enhances color development by catalyzing formation of Maillard reaction products. Sixth, undesirable volatile components, such as sulfur-containing aroma compounds, are removed. Finally, prolonged boiling causes evaporation of water and concentration of the wort. Because the mash or wort is diluted by sparge water, evaporation returns the density or specific gravity back to the desired level.

As noted above, a trub or precipitate forms during the kettle boil step. In addition, the wort may also contain insoluble hop debris, especially if whole hops were used.The latter are removed via strainers or screen-type devices that may also allow for sparging and re-circulation. For hot trub removal, several separation systems can be used.The simplest method is sedi mentation, but this is not a very efficient process. A much more efficient method is to centrifuge the hot wort using continuous centrifuges. Such units, however, are expensive and require frequent maintenance. The most common means of separating out the hot trub is the whirlpool separator, which is typically a low-height, conical-shaped (cone pointing downward) tank whose geometry promotes whirlpool-type movement of the wort.The trub or precipitate collects in the center of the tank.

After the trub is removed, the wort is cooled in plate-type heat exchangers. During the cooling stage, when the wort reaches about 50°C, more precipitated material forms (known as the "cold break"), which is separated by cen-trifugation or filtration.When the wort temperature is reduced to 10°C to 15°C, it is pumped into fermentation vats, where it is, at last, ready to be made into beer.

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