The object of "mashing" is to bring the starchy material into a condition favourable for its conversion into sugar and other products by the enzymes present, and eventually to effect this conversion.

In Continental practice the starchy substances - potatoes, maize, rice - are generally steamed under pressure to gelatinise the starch, as a preliminary to the mashing operation. Any other cereals used may be similarly treated for convenience of obtaining a concentrated mash, although with malt, barley, wheat, and oats actual gelatinisation is not necessary for attack of the starch by diastase.

The steaming is usually effected in a conical iron vessel known as a "converter," which is commonly of a size to take a charge of two or three tons of potatoes. In this vessel the potatoes are prevents the softened grain settling down and blocking the discharge tube. The steaming takes about two hours. Sometimes the operation is divided into two stages, the charge being passed into an intermediate converter for completion of the gelatinisation before being blown into the mash-tun. Here it is stirred and cooled as above described, until the proper temperature for saccharification is attained.

1 F.P. 459634 and 459815, Sept,, 1912, subjected to the action of steam at a pressure of three atmospheres during forty-five minutes or so, the temperature rising to about 135°. On opening the discharge valve at the bottom of the converter when the steaming is finished, the softened mass of potatoes is forced out by the pressure, and passes through a grid or cutting arrangement which helps to complete the pulping of the mass. The latter goes then to a mash-tun fitted with rotating stirrers, where the gelatinisation finishes as the mass cools down. The cooling is effected by water flowing through "attemperator" coils in the tun, or, in some forms, by means of an external water-jacket.

Maize, rice, and other cereals, since they contain less water than potatoes do, are mixed with one or two parts of water before steaming. If very dry, maize may be first steeped in water for a day; and if the steam pressure for the converter is limited, the grain may be coarsely ground before treatment with water. Moreover, the product obtained by steaming maize is liable to form a stiff, unworkable paste on cooling down, and to obviate this a little malt (0'5 to 1 per cent.) is added in order to effect a partial saccharification. Alternatively, a small quantity of hydrochloric acid, equivalent to about 0 2 per cent, of HC1 calculated on the weight of the maize, may be used instead of malt. The effect of the acid is to convert the basic phosphates of the grain, which are said to be chiefly responsible for the partial solidification of the pulp or paste, into acid salts. The coarsely-crushed maize is mixed with the requisite quantity of water, to which the hydrochloric acid has been added, at a temperature of 50-60°, kept stirred by means of an air jet for an hour, and then run into the converter. During the steaming operation the maize is kept in motion by jets of steam or air entering at the bottom of the converter, a small valve at the top serving as outlet for the air; this

Fig. 17. - "converter."

For steaming potatoes, maize, etc., under pressure (Egrot and Grange).

The temperatures at which various kinds of starch are gelatinised are given by Lintner1 as follows: -

Dox and Roark, however, using an electrically heated chamber on a microscope slide, and taking the loss of optical anisotropy as indicating the point at which gelatinisation occurs, found that different varieties of maize have different temperatures of gelatinisation.2 The range found was from 641° to 711°. Probably therefore the temperatures in the above table are approximations only.