The action of diastase upon starch is one of hydrolysis, whereby the starch is converted into dextrins, maltose, and intermediate products. The changes involved are very complex. Much study has been devoted to them, and much discussion has ensued, but it cannot be said that there is even yet general agreement as to the exact transformations which take place. Nevertheless, the main outlines of the changes are established definitely.

The hypothesis most generally favoured as to the reactions which occur is one due to Brown and Morris.1 These investigators explain the action of diastase upon soluble starch, at mashing temperatures, as a progressive degradation proceeding as follows: -

The starch molecule is regarded as being composed of five "amylin" groups, each having the formula (C12H10O10)20. Four of these groups are arranged about the fifth.

1 Trans. Laboratory Club, 1890, 3, 83.

When attacked by diastase, the starch molecule first breaks up into its five component groups. One or-these is very markedly resistant to further attack ("stable dext in"); the four others ("amylin" groups) are more readily hydroslysable: -

The amylin groups are then progressively hydrolysed into "amyloin" or "maltodextrin" complexes. Each C12H10O10 group in its turn takes up a molecule of water, forming a inaltose group, C12H12O11, which, however, remains for the time attached to its amyloin complex. Thus this first stage would be: -

An intermediate stage, when more maltose groups have been formed, would give a different maltodextrin, e.g.,

(C12H12O11)10 (C12H10O10)10 in which the change has proceeded halt-way. The final maltodextrin would be

(C12H12O11)19

C12H10O10

As the hydrolysis proceeds, the complex maltodextrins break down into smaller molecular aggregations, which, however, retain all the characteristics of the maltodextrins. This goes on until the maltose stage is reached - that is, until all the C12H10O10 groups of a maltodextrin have been hydrolysed to C12H12O11 groups. Thus, for example, the particular maltodextrin last formulated above would, on taking up another molecule of water, give 20 molecules of maltose: -

It follows, therefore, according to Brown and Morris's views, that if diastase is allowed to act for a sufficiently long time on starch under proper conditions of temperature, the products will eventually be maltose and "stable dextrin," the latter being only very slowly attacked.

As already indicated, however, the reactions are complex, and other products than those mentioned have been found. Thus Ling and Davis1 have shown that dextrose also is formed by the

1 Trans. Chem. Soc, 1904, 85, 16.

F prolonged action of diastase on starch; and the production of an "isomaltose" (Lintner) or "dextrinose" (Syniewski) has also been noted. Baker and Hulton1 have found that when diastase acts on barley starch granules the products are maltose, dextrose, dextrins, and a dextrin-like carbohydrate having the same molecular weight as maltose.

Under the ordinary mashing conditions for brewing, where the action of the diastase is stopped by boiling the wort, there will be a considerable proportion of the intermediate maltodextrins present, as well as the maltose and stable dextrin. These maltodextrins are important to the brewer of beer, because they are less readily fermented than the maltose in the main fermentation, but are gradually broken down, and undergo a slow " secondary ' fermentation whilst the beer is stored in casks, and thus prevent it becoming "flat." The distiller's interest, however, lies in having as much as possible of the wort directly fermentable, in order to get the best yield of alcohol. Hence the wort is not boiled, but the diastase is allowed to act as fully as possible, and this not only during the mashing, but during the subsequent fermentation also, when, under the combined action of diastase and yeast, the remaining maltodextrins and even the "stable' dextrin are largely converted into fermentable sugars. Since the distiller's wort is not boiled, it is, as already mentioned, more liable to bacterial contamination than the brewery wort is, and hence arises the necessity for heating to a high temperature (68° or 75°) after saccharification; or, alternatively, for the use of hydrofluoric acid or other antiseptic.