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.
Somewhat above the bottom of the vat, a steam inlet pipe I enters, connected at its other end by a coupling i with a suitable steam generator (see Fig. 43). Preferably the outlet of this pipe is
screened by a perforated plate M so that it may not be clogged by the pulp. It is also best that a filling piece be placed at the junction of the bottom with the sides in order that there be no sharp corner from which the pulp may not be easily cleaned out.
The bottom of the vat may either have a discharge door at the side as in Fig. 44 or at the bottom, as in Fig. 41,
An under side view of the latter construction is shown in Fig. 42. The bottom of the vat is made in two parts or doors J K. These are held closed by a transverse bar L inserted at its end into a stirrup l' and supported at its other end by a button l, or other means.
While various forms of steam generators may be used, Fig. 43 shows a simple construction well adapted to the needs of a small distillery. D desig-
nates the brick work of a furnace, and A the boiler. This is so set that an annular space E surrounds the sides of the boiler, through which the products of combustion must pass.
The head of the boiler is connected by a pipe B and collar b to the steam inlet pipe I of the steaming vat, heretofore described, as by the collars b i.
A filling tube C enters the boiler and projects nearly to the bottom, and the water outlet-pipe b
with cock f leads off from the upper water line. The tube C forms also a safety valve, for if the steam pressure becomes too great in the boiler and connected vat, it will force water up and out through the tube. If, however, the water falls below the level of the lower end of the tube, steam will issue and warn the attendant that water is too low. It would be best however, to provide a steam gauge, whereby the pressure of steam in the boiler and vat could be accurately indicated. It is to be noted that when steamed the potatoes will swell and occupy more space and that the steam vat should therefore not be much more than two-thirds filled with potatoes.
With the steaming vat above shown, the potatoes are delivered mixed with a considerable quantity of water, but a better plan is to have a per
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