On treating the ground malt with water from 60 to 70 percent of it is dissolved, forming a sugar solution of varying strength according to the quantity of water used. The process of grinding and extracting the sugar with water is called "mashing." The density of the mash, aside from the undissolved solid matters (protein, bran, fat, germ, fiber), varies from 10 to 16 percent. The mash is now treated with sufficient quantity of hops, thoroughly stirred, and heated to a temperature of boiling. This temperature destroys the further action of the diastase and also kills all forms of ferment which may exist in the mash, so that it can be seeded with a pure culture of yeast to start the fermentation. Immediately after treating with the hops and cooling to room temperature the mass is treated with the proper quantity of yeast and allowed to ferment. As the fermentation takes place the temperature of the mass rises to a considerable extent, in fact, to such an extent that it is often advisable to keep the tubs cool or in a cold cellar. The escaping of the carbon dioxid produces an apparent boiling of the mass, forming a foam, and the production of large quantities of additional yeast cells. The fermentation is practically finished in from three to five days, according to the temperature.