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.
Starch is a compound which, from the chemical point of view, belongs to the class known as carbohydrates - that is, compounds in which the element carbon is associated by a chemical union with water. Starch is therefore a compound made of carbon, hydrogen, and oxygen, existing in the proportion of two atoms of hydrogen to one atom of oxygen. Each molecule of starch contains at least six atoms of carbon, ten atoms of hydrogen, and five atoms of oxygen. The simplest expression for starch is therefore C6 H5 O5.
The principal starch producing plants are the cereals, the potato, and cassava. With the potato may be classed, though not botanically related thereto, the sweet potato and the yam. Among cereals rice has the largest percentage of starch and oats the smallest. The potato, as grown for the table, has an average content of about 15 per cent, of starch. When a potato is grown specifically for the production of alcohol it contains a larger quantity, or nearly 20 per cent. Cassava contains a larger percentage of starch than the potato, varying from 20 to 30 per cent.
Under the microscope the granules of potato starch have a distinctive appearance. They appear as egg-shaped bodies on which, especially the larger ones, various ring-like lines are seen. With a modified light under certain conditions of observation a black cross is developed upon the granule. It is not difficult for an expert microscopist to distinguish potato from other forms of starch by this appearance.
The mineral matters which the potato extracts from the soil or from the fertilizers which are added thereto consist chiefly of phosphate and potash. The mean average composition of the ash of the potato is shown in the following table:
Soda (NaX)) ...........
Iron oxid. (FE2O3)
Phosphoric acid (P2O5)
Sulphuric acid (SO3)
Silicic acid (SiO2)
This analysis was made upon the so-called pure ash, deprived of its unburned carbon, and freed of sand and carbon dioxid.
Of all the common root crops, the potatoes, including the yam and the sweet potato, are the most valuable for the production of alcohol, meaning by this term that they contain more fermentable matter for 100 pounds than other root crops. This is shown by the following comparative statement:
Potatoes, sweet potatoes and yams .
Under the most favorable circumstances and with potatoes which have been bred especially for the purpose an average content of fermentable matter of about 20 per cent, may be reasonably expected. It is thus seen that approximately ten pounds of industrial alcohol can be made from one hundred pounds of potatoes. If sixty pounds be taken as the average weight of a bushel of potatoes, there are found therein twelve pounds of fermentable matter, from which six pounds of industrial alcohol can be produced, or six sevenths of a gallon. It has also been shown that at the prices quoted in 1905 the amount of Indian corn necessary for the production of a gallon of industrial alcohol costs not less than 15 cents. From this it is evident that the potatoes for alcohol making will have to be produced at a cost not to exceed 15 cents per bushel before they can compete with Indian corn for the manufacture of industrial alcohol.
The three principal steps in the manufacture of alcohol are (1) the preparation of the mash or wort, (2) the fermentation of the mash or wort drawn off from the mash tun, and (3) the distillation of the dilute alcohol formed in the beer or wash from the fermentation tanks. The preparation of mash includes (1) the treatment of the material used with hot water to form a paste of the starch or the sugar, and (2) the action of the malt or ferment on the paste to convert the starch into fermentable sugar.
The object of the mash tun is to reduce the starch in the ground grain to a pasty, gummy mass, in order that the ferment of the malt may act upon it vigorously and convert it into sugar. If the mashing be done before the addition of the malt the temperature may be raised to that of boiling water. If, however, the malt be added before the mashing begins, the temperature should not rise much, if any, above 140 degrees F., since the fermenting power is retarded and disturbed at higher temperature. The mashing is simply a mechanical process by means of which the starch is reduced to a form of paste and the temperature maintained at that point which is best suited to the conversion of starch into sugar.
The mash, after the starch has all been converted into sugar, goes into fermenting tanks, which in Scotland are called ' wash backs' when the yeast is added. They often have a stirring apparatus whereby the contents can be thoroughly mixed with the yeast and kept in motion. This is not necessary after the fermentation is once well established, but it is advisable, especially in the early stages, to keep the yeast well distributed throughout the mass. In these tanks the fermentations are conducted, the temperature being varied according to the nature of the product to be made. For industrial alcohol the sole purpose should be to secure the largest possible percentage of alcohol without reference to its palatable properties."
Consul John H. Grout, Odessa, Russia, says:
In the alcohol-distilling industry of Russia potatoes are annually increasing in importance. the alcohol produced therefrom exceeding that produced from all other sources.
Aside from the large quantities of potatoes purchased every year by the factories from peasant producers and estate owners whenever these may have a surplus which they cannot more profitably dispose of, there are large plantations devoted solely to the production of potatoes for distilling purposes, there being also a tendency to increase these plantations.
The potato crop of 1910 for European Russia was greatly in excess of that of the previous year, which was also a good one, and the quality of the tubers was in most districts better than in 1909. It is generally supposed that the climate of Russia is favorable for the production of potatoes in vast quantities, and that, with the aid of fertilizers, their production can be increased to meet all demands of distillation, the production of dena-turized sprits for industrial and illuminating purposes now being only in its infancy."