Wort is an aqueous solution of extract made from grain, intended for fermentation by yeast into beer. For most beer styles, the finished wort that reaches the fermentation vessel is between 80% and 90% water by weight. Wort is created by the process of mashing and then separated from grain husk material in the lautering process. See lautering and mashing. Wort is then collected in the brew kettle, where it is boiled with hops. See kettle. When yeast is added to cooled wort, fermentation transforms the hopped wort into beer.
The composition of the wort depends on the composition of the grain bill, the mashing process, the brewing water, and the hops. A standard all-malt wort will contain approximately 12% monosaccharides, 5% sucrose, 47% maltose, 15% maltotriose, and 25% higher saccharides, such as dextrins. Most of these wort sugars are produced in the mash tun, where enzymes in the grain convert starches to sugars. See enzymes, saccharification, and sugar. Mash temperature and thickness will have large effects on the sugar profile of the wort, and this will affect the wort’s fermentability. Some beer styles call for the addition of non-grain-derived sugars—both fermentable and unfermentable—to the wort to give the finished beer extra flavor and/or to develop a higher alcohol content without heaviness of texture. Besides carbohydrates, wort components include nitrogen compounds (mostly proteins), salts and minerals, acids, phenols, hop bitter substances, hop essential oils, and lipids.
Other grains aside from barley, including wheat, rye, or oats, may be part of the mash and thus become part of the wort. Many beer styles are brewed with the addition of adjuncts such as corn grits or rice, which require specialized brewhouse equipment, including dedicated mills and cereal cookers to generate a fermentable wort. See adjuncts. Several mash raw materials such as sorghum or buckwheat can produce gluten-free wort for gluten-free beer. See buckwheat, gluten-free beer, and sorghum.
Wort is physically and microbiologically unstable. Boiling renders wort sterile, preparing it for the introduction of brewer’s yeast. The wort boil also extracts bitterness, flavors, and aromas from hops, concentrates the wort through evaporation, drives off unwanted volatiles and off-flavor precursors, denatures malt enzymes, and causes the coagulation of proteins and phenolic substances that can later be removed.
The kettle boil also has the effect of darkening the wort’s color and deepening its malt flavors as a result of the Maillard reaction. See maillard reaction. The pH of the wort drops as well largely because of the precipitation of calcium phosphate. In most worts, the drop is from roughly 5.6 to 5.8 to roughly 5.2 to 5.4, a pH range that is acceptable to most yeast strains for the start of fermentation. See fermentation and yeast.
Hops are added to the brew kettle as cone hops, pelletized hops, or liquid extracts, usually in several doses at different stages of the boil. Hops contain dozens of bittering, flavor, and aroma compounds that are extracted from the plant material during the boil. See alpha acids, aroma unit (au), and hop oils. If brewers use herbs and/or spices in their beers, they too are usually added to the boil. See gruit, herbs, and spices.
The next important function of the boil is to coagulate malt proteins, which gather into visible flocs called hot break or trub. See hot break and trub. Trub also contains phenols and tannins as well as spent hop material. Much of the trub settles out at the bottom of the brew kettle. Traditionally, this would have been removed by recirculating the wort through a bed of whole flower hops, allowing the hops to act as a form of filter. This is still practiced at many small breweries. These days, however, trub is usually removed from the wort in a special vessel called a whirlpool into which the hot wort is pumped tangentially at high speed after the kettle boil. See whirlpool. Trub particles and hop fragments are forced to the sidewalls and finally to the center of the whirlpool floor. Clear wort is then siphoned off through an outlet near the edge of the whirlpool floor and sent through a heat exchanger for cooling. See heat exchanger. Once it is cooled to fermentation temperature, the wort is aerated or oxygenated and then usually pumped into a fermentation vessel, where the yeast transforms wort into beer. See fermentation. Some wort may also be moved directly into a packaging area to become an unfermented non-alcoholic malt beverage, such as Malta. It can also be moved into a vacuum evaporator to be concentrated into a syrupy malt extract, widely used in the food industry and by homebrewers.
For most beer styles, the finished wort that reaches the fermenter has a gravity between 9°P and 16°P, but some strong beer styles call for much more concentrated worts, with some barley wines produced from worts of more than 30°P.