The ordinary alcohol of commerce (ethyl alcohol) is chiefly obtained by the fermentation of some form of sugar through the action of yeast. The sugar may be already existent in the raw materials employed; it is so, for instance, in grape juice, beet juice, and molasses. Other raw materials, however, may not contain sugar as such, or may contain it in trivial quantities only. Thus in cereals and potatoes, which are some of the chief sources of alcohol, the utilisable substance is starch; and in sawdust or wood-pulp, other sources, it is wood-cellulose. But whether starch or cellulose, the material must be converted into sugar before it can be fermented by yeast to produce alcohol.

Starch, in fact, is the source of by far the larger part of the sugar from which alcohol is eventually obtained, and it will be useful to give forthwith, in a few words, a preliminary idea of the chief process by which this raw material is converted into the finished product. The various phases of the operation will afterwards be dealt with in greater detail.

The starchy material is first ground, and heated with water to gelatinise the starch. This forms the "mash," which is then saccharified by means of malt, the conversion of starch into sugar being effected through the action of an enzyme, diastase {amylase), which is present in the malt. The resulting liquid is now known as the "wort"; it is essentially a solution of sugar (maltose) with dextrin and other ingredients obtained from the starchy material.

Next, the wort is fermented by adding yeast ("pitching"). As a result of the fermentation, the sugar is converted into alcohol through the action of certain other enzymes (maltase; zymase) which are present in the yeast. The fermented alcoholic liquid is termed the "wash." Finally, the wash is distilled to separate the alcohol, and the latter, if necessary, is subsequently "rectified" by further distillation to such a degree of strength and purity as may be desired.

If molasses or other sugar-containing material is being us and instead of starch, the preliminary saccharification stages are ture course, unnecessary. A solution of the material is prepared con-contain a suitable proportion of sugar, and fermented directly. asitic

We now proceed to describe more fully the materials and udies cesses employed, and the principles underlying the various opd he tions.

I - Materials Employed

The possible sources from which alcohol can be obtained areh very numerous, since any substance containing either sugar or starch may be used for the purpose. Moreover, not only sugar and starch, but wood and other cellulose-containing materials are also in use as sources of alcohol, and synthetic alcohol from hydrocarbons is emerging out of the purely experimental stage and becoming, or promising soon to become, a regular commercial product.

Sugar and starch, however, are foodstuffs, and they, or the substances containing them, may for this reason sometimes and in some places be too expensive for use in making alcohol. Thus comparatively little wheat is employed for the purpose anywhere. Potatoes are very largely used on the Continent for making alcohol, but in this country scarcely at all. They command here a higher price for ordinary consumption than the distiller will pay. Be finds maize and molasses more economical, in spite of the fact that they are not indigenous products, whilst potatoes are so. Moreover, many of the substances which contain starches and sugars do not contain a sufficient proportion to make it profitable, in normal circumstances, to use them in spirit manufacture.

Hence, in spite of the great number of articles from which it is possible to obtain alcohol, the materials actually employed to any large extent are comparatively few. They may be grouped into the following classes: -

(a) Starch-containing materials.

(b) Sugar-containing materials.

(c) Cellulosic substances.

(d) Synthetic materials.

A tabular botanical summary of the first two classes will be found at the end of this section (p. 22).

(A) Materials Containing Starch

Of these, cereals and potatoes are the principal substances used in making alcohol.

The chief cereals employed for the purpose are barley, maize, oats, rice, rye, and wheat. Naturally they vary in their content starch, and in large distilleries the calculations as to yield are ed upon analysis of the actual consignments of grain in use.

average values may be taken as approximately the following: -

Starch, per cent.

Barley........................................................

60

Maize ................................................................

63

Oats............................................................

53

Rice..........................................................

67

Rye..........................................................

63

Wheat.......................................................

65

Green malt..............................................

40

Dry malt....................................................

68

Barley is used in large quantities for malting and in the making of potable spirits. For industrial alcohol, it is too expensive to be used by itself on a large scale.

Wheat, for the same reason, is employed to a relatively small extent, and chiefly for special spirits. On the Continent, for instance, malted wheat is used for making "Geneva" spirit, and also in brewing certain kinds of beer.

Maize is used very largely, both in Europe and in America. It is so easily grown in the latter country, and stands storage and carriage so well, that it has become pre-eminently a raw material for distillers' use.

Oats are rather extensively employed in this country, and rye on the Continent; whilst rice is often cheap enough to be used on a large scale, here and abroad. Other kinds of grain used to an important extent are millet, and sorghum grain or dari.

Potatoes contain on an average about 20 per cent, of starch, the amount ranging usually from 15 to 24 per cent. They are very largely used on the Continent for the making of alcohol. In Germany, where about eight million acres of land are devoted to potato cultivation, more than four-fifths of the total alcohol produced (84 million gallons in 1913) is derived from potatoes, of which some 3 million tons per annum are used for this purpose. In Russia the principal sources of alcohol are potatoes and rye.

Not much alcohol is produced from potatoes in France, where the chief raw materials are sugar-beet, molasses, maize, and wine. In this country, barley, oats, maize, rice, and molasses are the main substances used. Maize is the principal starchy source of alcohol in the United States.

In the tropics, starch plants such as cassava (manioc) and arrowroot are comparable with potatoes as regards starch yield, and are expected to become more and more important as sources of alcohol. Manioc, in fact, is already employed to some extent in Europe for the purpose. The cassava tubers are about 8 to 10 lb. in weight.

c 2

They contain approximately 25 per cent, of starch, and from 4 to 6 per cent, of fermentable sugars.

An acre of ground yielding a crop of five tons of potatoes will furnish about one ton of starch, equivalent to 160 gallons of absolute alcohol theoretically, or approximately 130 gallons in practice. From barley and oats, the yield of starch per acre of land is much less, lying between one-third and one-half of the foregoing quantity. Maize, taking the average yield at 27 /2 bushels (56 lb.) per acre, and the starch plus sugar at 65 per cent., will give 1000 lb. of fermentable matter for each acre. An average acre of cassava, however, is stated to yield 10 tons of tubers, giving about 5000 lb. of extractable starch,1 or more than double the amount obtained from an average acre of potatoes.