This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
It is the opinion of Secretary of Agriculture James Wilson and other close students of the food supply of the world that there should be some way of preparing and preserving potatoes that stocks may be carried over from the "fat" (large producing) to the "lean" (small producing) years. This would balance or equalize supplies to guard against possibility of famine or an approach to it because of crop shortage in densely populated countries.
In the Daily Consular and Trade Reports of the Bureau of Manufactures of the Department of Commerce and Labor, February 19, 1910, Consul Thomas H. Norton, of Chemnitz, describes a process recently introduced by a Prussian firm by which potatoes may be converted into a dry concentrated meal. He writes as follows:
The potato occupies a relatively more important position in Germany than in other European countries. It is not only employed largely for food for both man and beast, but also for conversion into starch and alcohol. The 1908 crop was estimated at 46,500,000 metric tons (51,256,950 short tons), 13,000,000 tons being used for human food and 19,000,000 tons for feeding domestic animals. Starch factories utilized 1,500,000 tons, distilleries 2,500,000 tons, while 5,500,000 tons were required for seed. There remained 5,000,000 tons, lost by decay, freezing, etc. German economists have recognized the extent of this national loss, of about $28,500,000 in value, especially because the empire now imports annually about $72,000,000 worth of cattle fodder. Nearly 40 per cent. of this sum, paid to foreign agriculture, could be saved if the loss by subsequent decay in the harvest potato crop could be prevented.
Numerous processes have been submitted in response to an offering of prizes amounting to $6,000. These are based upon two distinct methods of treatment. In the first, sliced potatoes are exposed to the current of hot gases from a furnace; in the second, the flake process, potatoes are more finely divided, and dried at a lower temperature with the aid of steam coils. This last method is costly. The product of the first method, while available for industrial purposes, is not fully satisfactory for use as a fodder.
A process recently patented and introduced by a Prussian firm seems to have successfully overcome the disadvantages of the earlier systems. The essential features consist in the use of pressure combined with a vacuum for withdrawing the bulk of the water in potatoes, the further drying of the residue by artificial heat, and the isolation of albumen found in the press liquor. This process has been tried with excellent results on an industrial scale.
The plant employed is comparatively simple. The potatoes are first thoroughly washed in a large vat provided with a stirring apparatus. Thence they pass into a mashing machine, and the pulpy mass is pumped into a reservoir, and from this is fed through a large funnel into the suction machine. The latter is the central feature of the plant and presents a somewhat novel form of utilizing the vacuum principle. It consists of two hollow cylinders, one immediately above the other. The exterior is made of perforated plate similar to that employed in centrifugal machines and filter pumps, and is covered with linen filtering cloth. A pipe connects the interior of each cylinder with an air exhaust. The interior spaces are, however, divided into segments, and the construction is such that the lessened pressure in each segment is felt when it is in immediate contact with the companion cylinder. As the potato pulp passes between the two cylinders, not only their pressure, but also atmospheric pressure, removes nearly all liquid. The residual mass falls into a trough and is conducted by a helical conveyor to small cars. These pass into a hydraulic press, where the mass is finally deprived of all water capable of removal by pressure.
From the press the potato mass is transferred to the drier. This consists of a cylindrical chamber, within which there is a revolving drum, divided horizontally into ten sections. The upper seven sections are heated by connection with a series of steam pipes; the lower three are cooled by means of a similar series, through which water circulates. The pressed potato cake is continuously fed into the top section. From this it gradually descends through openings into the lower sections, one after another, until it finally issues from the bottom compartment and is conveyed to storage rooms. The construction of this revolving drum is such that prongs attached to its axis continually stir up and crumble the nearly dried potato cake, so that it is in coarse grains when it leaves the apparatus. At the same time, by means of properly directed air currents and the aid of the elevated temperature in the upper seven sections, nearly all moisture remaining after the treatment in the press is effectively removed.
The resultant coarse potato meal has one quarter of the original weight of the tubers employed, and occupies one eighth of the space. It has an odor and taste similar to that of freshly made bread. It may be used or kept in this condition, or can be pressed into compact cakes for convenience in transportation. The chemical analysis of potato meal, dried as above described, gives the following percentages: Water, 11.50; fat, 0.31; protein, 3.73; ash, 2.06; fibre, 1.71; carbohydrates, 80.69.
Pressed potato cake is easily broken up by hand, and can be fed to animals, alone or mixed with other forms of fodder, preferably after moistening with a little water, when it is at once softened.
By the combined processes of pressure and suction nearly three quarters of the weight of raw potatoes are removed in the form of a cloudy liquor. This portion is allowed to stand in reservoirs until all traces of starch have settled to the bottom. The clear liquor is then boiled and filtered with the aid of a vacuum apparatus. A precipitate is obtained of crude protein amounting to about 2 per cent. of the original weight of the tubers. By proper treatment this yields about 80 per cent. of technically pure albumen, which is constantly in demand in German markets.
The residual liquors from the protein precipitate contain small amounts of sugar, salts, and nitrogenous matter. They can be advantageously used for irrigation purposes on agricultural lands.
The plant requisite for the treatment of 10,000 tons of potatoes during a season of about eight months costs $18,000 to $19,000. The machinery alone, without a press for transforming the meal into cakes, costs $12,000. For a building, $3,000 suffices, and the remainder is needed for pumps, motive power, washing vats, etc.
The force needed to operate the plant consists of seven men, and includes one engineer, a stoker, one helper, one workman in the potato cellar, two to attend to the machines, and one to handle the residual liquors. If the final product is to be pressed into cakes, the additional cost of the plant is about $4,000, and two more operatives are required. Such an installation can naturally be operated with great economy in connection with a distillery or starch factory.
In practice it is found that the total cost of preparing unpressed potato meal by the above method (including interest, depreciation, etc.) is $0.56 per long ton of tubers. The additional cost for pressing into cakes is $0.12 per ton of potatoes. In estimating the cost of the fodder thus produced it is, of course, necessary to deduct a certain sum for the albumen extracted from the residual liquor, as mentioned above. When potatoes are to be raised for supplying regions more or less remote with cattle fodder the advantage of having the nutritive constituents of the tuber in a concentrated form is obvious. Thus, in practice, 3.8 tons of raw potatoes yield one ton of the desiccated product. The freight charges in Germany for transporting (in carloads) the 3.8 tons a distance of 100 kilometers (62 miles) are $3.07. The freight charge, under similar conditions, for the one ton of meal would be $0.81. Adding to this the cost, 56 cents per ton, of treating the 3.8 tons of raw potatoes, or $2.13, the total expense of delivering the fodder would be $2.94. At the comparatively short distance of twenty-six miles there is then a distinct economy in shipping the meal instead of tubers. With every increase in distance there would be a proportionate increase in the saving.
In these days of rising values for all meat products there is a prospect that the newly introduced process will aid materially in decreasing the cost of cattle raising in various sections of the empire, where stock raisers are largely dependent upon fodder transported from a distance."
The manufacture of desiccated potatoes has been started in the United States.
C. F. Langworthy, in "Farmers' Bulletin 295," .says:
Potatoes are so valuable in the diet that many attempts have been made to put them into a compact form in which they can be kept for a long time. This is usually accomplished by drying them, which both preserves them from decay and reduces their bulk. One of the oldest of such preparations is one long used in Peru and known as chunno. To make it, part of the juice is pressed out of the potatoes, which are then dried in the air until they are reduced to about one fourth of their original weight. There is a variety of similar preparations in American and European markets, and although the mode of procedure differs considerably in the various brands the main principle is the same - namely, to check bacterial action. The changes which we call decay are caused mainly by the development of bacteria. These can reproduce only where there is moisture and warmth present. Therefore, if the moisture is removed, their growth is retarded. The fact that the bulk of the potatoes is reduced at the same time is especially advantageous because such dried preparations are used mainly for camping expeditions, long sea voyages, and under other conditions where storage space is at a premium. The composition of such desiccated or evaporated potatoes is practically that of the original tubers minus more or less of the water. Of course, if extreme heat is used in the preparation, part of the starch may be changed to dextrin and there may be other minor changes in the chemical composition. There is no reason to believe that these decrease the nutritive value. Various kinds of desiccated potatoes have been studied at the California Agricultural Experiment Station. Their water content ranged from 4.8 to 7.9 per cent. and their total carbohydrates from 77.9 to 80.6 per cent. In fact, their general composition was not unlike that of good white flour. They contained slightly less water, protein and fat, slightly more carbohydrates, and noticeably more mineral matters. Of course desiccated potatoes are supposed to be soaked in water before using and in this way regain somewhat their original characteristics. While their flavor and appearance cannot equal these of good fresh potatoes, they are considered very appetizing and acceptable where fresh ones are unobtainable.
Chemical substances are sometimes used for improving the color (i. e., 'bleaching') of desiccated potatoes. While a small quantity of these may be harmless, their continued presence in the diet might be very dangerous, and their use is not to be recommended.
Canned potatoes are on the market and are prepared for use in camps or wherever it is not convenient to cook food. They also may be kept in good condition for a long time. In composition such goods do not differ from similar freshly cooked potatoes."