The degree of temperature employed in drying and roasting the barley determines the colour and commercial character of the malt, which may be pale, amber, brown or black. In the United States the light-coloured varieties of malt are chiefly made. An important change which takes place during the malting of barley is the conversion of its albuminous constituents into a peculiar ferment, termed _diastase_, which, although its proportion in malt does not exceed 0·003 per cent., exerts a very energetic action in transforming starch, first into dextrine, then into sugar (maltose). The following analyses, by Proust, exhibit the general composition of unmalted and malted barley:-- ----+---------------------+---------------+-------------+---- | | Barley. | Malt. | | +---------------+-------------+ | Hordeine | 55 | 12 | | Starch | 32 | 56 | | Gluten | 3 | 1 | | Sugar | 5 | 15 | | Mucilage | 4 | 15 | | Resin | 1 | 1 | | | --- | --- | | | 100 | 100 | ----+---------------------+---------------+-------------+---- The body termed hordeine is generally considered to be an allotropic modification of starch. In the brewing of beer, the malted grain is crushed by means of iron rollers, and then introduced into the mash-tubs and digested with water at a temperature of about 75°, whereby the conversion of the starch into dextrine and sugar is effected. After standing for a few hours, the clear infusion, or _wort_, is drawn off and boiled with hops (the female flower of _Humulus lupulus_), after which it is rapidly cooled, and then placed in capacious vats where it is mixed with yeast and allowed to undergo the process of fermentation for several days, during which the formation of fresh quantities of yeast and a partial decomposition of the sugar into alcohol and carbonic acid take place. The beer is next separated from the yeast and transferred into clearing-vats, and, later on, into storage casks, where it undergoes a slow after-fermentation, at the completion of which it is ready for consumption. The quality of the water used in the process of mashing and brewing is of great importance, and it is of special moment that it should be free from all organic contaminations. The presence of certain mineral ingredients, notably of calcium sulphate, is believed to exert a beneficial effect on the character of the beer obtained.