Unmalted cereal grains such as rice, corn, wheat flour, or some form of barley are sometimes added to the malt in order to change the various qualities of the beer. Heated water is added so that the starches are converted to fermentable sugars. A high water temperature at this point produces a beer with less alcohol but more flavor. In a process called lautering, the mash is then filtered into a brew kettle, and the liquid is called the wort. Hops are boiled with the wort to give the liquid a bitterness, aroma, and color not provided by the cereals or fermentation process.
Hops also act somewhat as a preservative.
The hop cones are removed after the boiling process and are used in making fertilizer. The leftover wort, called bittered wort, is pumped through a cooling system and filtered again. Bittered wort is fermented by the addition of strains of yeast. When most of the fermentable material has been converted to alcohol, the beer is transferred to tanks for a slow, secondary fermentation, during which carbon dioxide is produced. After a period, called lagering, of several days to several months, the beer is ready for final processing and packaging.