Diastase, therefore, is elaborated by the scutellar epithelium during the growth of the embryo. It attacks the starch of the endosperm, and renders it soluble, so that the products can now diffuse through the water present and reach the embryo, there to serve as aliment for the young plant. The attacking of the starch has been facilitated, and indeed made possible, by the previous softening action of the cytase on the starch cell-walls, as the latter in their normal state are not permeable to the diastase.1

By experiments on somewhat similar lines to those described, it has further been shown that during germination there is also a transference of a part of the nitrogenous constituents of the barley grain from the endosperm to the embryo. Thus in barley which had been on the malting-floor for nine days, about one-third of the to al endosperm nitrogen was found to have migrated to the embryo. There is, in fact, a development of proteolytic enzymes (peptone and tryptase) during germination, and these convert a proposson of the insoluble proteins of the grain into simpler substances, such as proteoses, peptones, and amino-acids. These proteolytic enzymes, there is good reason to believe, are, like the diastase and cytase, secreted by the scutellar epithelium.

1 So so Mann and Harlan on the " Morphology of the Barley Grain," U.S. . Agr. Bull., No. 183 (1915). A reprint of this is given in J. Inst.

Brewi 16, 22, 73.

The simpler products into which the protein is converted arc soluble in water, and hence in malt there is a larger proportion of soluble nitrogenous bodies than in the original barley; in fact nearly double as much. Thus Bungener and Fries found the "soluble " nitrogen in a specimen of barley to be 0 355 per cent., and in the malt made from it, 0 642 per cent. The total amounts of nitrogen in the barley and malt were 1.69 and 1.58 per cent, respectively. The importance of the production of soluble nitrogenous compounds during malting lies in the fact that they pass into the wort when the malt is mashed, and serve as nitrogenous nutriment for the yeast during the subsequent fermentation.

Summing up, then, we find that during the germination of barley, enzymes of three classes are secreted by the embryo: (1) a cellulose-dissolving enzyme cytase, which attacks the walls of the starch cells and makes them permeable to diastase; (2) a diastatic enzyme. malt-amylase or diastase, which can convert starch into sugars and other soluble matters; and (3) proteolytic enzymes, peptase and tryptase, which convert a portion of the insoluble proteins of the grain into simpler, soluble nitrogenous substances. By these means the whole solid contents of the endosperm can be broken down and utilised by the young plant.

"The art of the maltster," Dr. H. T. Brown remarks, " consists in directing, co-ordinating, and limiting these natural physiological processes of interaction between the embryo and endosperm, and making them as far as possible subservient to a particular end ' - namely, the production of a friable malt, which will yield the maximal amount of extract of the right composition for the special purpose in view.

This purpose is not the same for the distiller as for the brewer. It has already been seen that the former uses "long" malt, which has been germinated for a more extended period than the brewer's "short ' malt, and has therefore produced more diastase. The aim of the distiller is to produce alcohol; that of the brewer is to make a beverage which contains as essential ingredients no only alcohol but other substances derived from starch, namely destrins and malto-dextrins. These impart "body" and palate-fulness to the beer, and provide material for the secondary fermation which it undergoes in the cask. In fact the flavour and charecter of beer depend quite as much on the presence of unfermented dextrins and other extractive matters as they do on the fermented alcohol which the beverage contains. Hence the brewer not want completely to convert all the starch of his grain into sugar: his wort must not be wholly fermentable. The brewer's malt is therefore not germinated to produce the maximum of diastase, and moreover it is heated on the kiln to a temperature which destroys much of the diastase that has been formed. On the other hand, the distiller wishes to convert the whole of his starchy material into alcohol; any not so converted is mere loss. He looks upon his malt as, essentially, a source of diastase, used for the purpose of transforming the starch of raw cereals or of potatoes as completely as possible into fermentable sugars.

Hence distillery malts are usually germinated long enough to produce the maximum amount of diastase, and are preferably used as "green" malts, or, if kilned at all, only at the lowest practicable temperature. The higher the temperature used in drying the malt, the greater is the loss of diastatic power. This is especially so if the heat is applied too quickly, while the malt still contains much moisture; because diastase when moist is very sensitive to the action of heat. Green malt, however, can only be employed to a limited extent for making malt whisky, since the special flavour of this is due mainly to the use of kilned malt. In distilleries which make compressed yeast, too, a proportion of kilned malt is employed.

Ordinarily, the diastatic power of green malt is from 110° to 125° (Lintner's scale). In brewery malts it is reduced by the kilning process to less than one-fourth of this amount, ranging generally from 20° to 40°. Distillery malts, and also malts used by vinegar-makers, have usually a diastatic power of 80° upwards.

Diastatic power of malt ("Lintner value"). - This is determined in a conventional manner by allowing an extract of the malt, prepared under standard conditions, to act upon a 2 per cent, solution of soluble starch for an hour at 21.1° (70° F.). The quantity of starch converted is then estimated from the volume of the converted liquid required to reduce a given volume (5 c.c.) of Fehling's solution. So long as the maltose produced does not exceed 45 per cent. of the starch used, this maltose may be taken as a measure of the diastatic activity of the extract (Kjeldahl). The modus operandi recommended by the Malt Analysis Committee of the Institute of Brewing is as follows.1