Diastase (Gr. suotnu, to separate), a peculiar principle which is formed during the germination of seeds. It is most abundantly produced in the cereals, particularly in barley. It is formed at the base of the sprout, by a change which takes place in the albumen within and about the germ by the action of the vitalizing principle which has been awakened within it by heat and moisture. For the mode of producing diastase, see Brewing. It may be extracted from malt by steeping in water at about 80° F., when it will be dissolved together with an albuminous body. A pasty mixture is produced, which is pressed, and the liquor filtered and heated to about 170°, to coagulate the albuminous body, and again filtered. This filtrate contains the diastase, and may be used for obtaining the peculiar effects of that body; but to obtain it in a pure state it is precipitated from the solution by the action of absolute alcohol. It is a white, amorphous, flocculent substance, soluble in water and dilute alcohol, but insoluble in absolute alcohol, tasteless, and easily decomposed.

Moistened starch, when subjected to the action of only a minute quantity of it (one part in 2,000, according to Payen and Persoz), at 150° F., soon becomes disorganized and converted into soluble starch, dextrine, and grape sugar. Diastase in solution changes so readily that it soon becomes acid and loses its power of transforming starch. It is destroyed by boiling its solution; an important fact, which is taken advantage of in the manufacture of dextrine, to arrest the transformation when the production of that substance has reached the greatest practicable amount, and also in the brewing of beer, for the purpose of preventing fermentation during the cooling of the wort. It has never been obtained in such a condition as to afford a satisfactory analysis. According to the above authorities, the amount of nitrogen varies, being less when the substance has been carefully prepared. From this fact, and from the convertibility of starch into glucose by several other substances, it has been suggested that instead of being a principle of definite composition, it is probably an albuminous compound, passing through a change or series of changes.

This view is strengthened by the discovery, by Dubrunfaut, of another substance in malt, similar in its effects, which he has called maltine, and finds to be even more active than diastase; an equal quantity being capable of effecting ten times as much transformation. He also obtained a third but less active substance than diastase, and believes the latter and the other two substances to be the same body undergoing decomposition. The action of alcohol when used to precipitate the diastase destroys the so-called modifications.