[CHAPTER VII.]
Alcohol from Potatoes.
In certain countries, as for instance Germany and France, potatoes form the greatest source of alcohol, particularly for industrial purposes. With the possible exception of corn and beets they will probably be most used in America.
The best potatoes for distilling are those which are most farinaceous when boiled. In other words, those which are “mealy” and most appetizing. These give the largest yield of alcohol per bushel. The best season of the year in which to use potatoes is from October to March, when they germinate.
The potatoes should be kept in dry cellars, and at even temperatures, warm enough to prevent freezing and yet not so warm that they will rot or sprout. Diseased potatoes may however be used, if they have not been attacked by dry rot, though they are not so easily worked. Frosted potatoes may be also used, but they must not have been completely frozen.
Before being steamed, the potatoes should be washed, either by hand or by a machine, care being taken to remove all stones, clods of earth, and other foreign substances which might impede the subsequent operations.
There are three main methods of saccharifying the fecula or starch of the potato. The first and most important by reducing the tubers to a pulp, and malting the entire mass. The second and third, by rasping the potatoes and so separating the fecula or starch grains from the mass, and then making a thin liquor or wash containing this fecula.
Originally, in the first process, the washed potatoes were submitted to the action of boiling water, but later cooking by steam at a temperature of 212° F. was used, as being much more convenient to handle and more effective in action. The object of steaming is to break the coating and reduce the contents thereof to a pasty condition, wherein the starch is more effectively acted on by the malt and yeast. Ordinary steaming does not, however, render the pulp sufficiently pasty; some of the starch remains undissolved and is lost, hence in the modern practice, steam is turned into the steaming vat under a pressure of three or four atmosphere (45 to 60 lbs. to the square inch).
High pressure steaming will be later described but the simple and older method of mashing and apparatus therefor, used prior to 1870, was as follows:
Fig. [41] shows a section of a steaming vat. This consists of a conical wooden tub H provided at its top with a suitable cover O having a trap or door P for putting in the potatoes. This as shown, consists of a hinged lid, having a button p or other fastening means. This lid and cover should be of course steam tight, and it would be better to have it clamped down by a screw clamp than held by a button.