The above data show the average content of fermentable matter in German potatoes, as determined by three of their leading authorities, to be about 20 percent. The potatoes used for the manufacture of alcohol in Germany are not of the variety raised for edible purposes. In a large number of experiment stations in Germany systematic efforts have been made for many years to grow a potato rich in starch without respect to its edible qualities. These potatoes are coarser in structure and less palatable than those grown for the table. The object of the cultivation of this class of potatoes is to produce as much starch and other fermentable matters per acre as possible. It is evident that our own experiment stations should undertake work of a similar character if the potato is to be used to any great extent in the manufacture of industrial alcohol. There is no doubt of the fact that success equal to that attained by the German experimenters will attend any systematic efforts of this kind in our country. Not only will larger crops per acre of potatoes be grown, but these potatoes will contain larger quantities of starch and other fermentable substances. If the crop of potatoes is to remain at the present average, namely, less than 100 bushels per acre, profitable returns for alcohol making can not be expected, either by the farmer or by the manufacturer. A much larger quantity must be grown and, if possible, at less expense, in order that encouraging profits may be realized.
Maercker, one of the most celebrated of German authors, states that in certain instances the potato in Germany reaches a very high starch content. Some varieties, in exceptional instances, have shown as high as 29.4 percent, 28.1 percent, and 27.3 percent, respectively. In warm, dry seasons potatoes often are found containing from 25 to 27 percent of starch. According to Maercker, the sugar content, including all forms of sugar, varies greatly. Perfectly ripe potatoes contain generally no sugar or only a fractional percentage. When potatoes are stored under unfavorable conditions, large quantities of sugar may be developed, amounting to as high as 5 percent altogether. In general, it may be stated that the content of sugar of all kinds will vary from 0.4 percent to 3.4 percent, according to conditions.
While potatoes grown thus to increase the content of starch are not generally used as food, yet they are nutritious but not as palatable as those grown especially for table purposes.
Ash analyses: The mineral matters which the potato extracts from the soil or from the fertilizers which are added thereto consist chiefly of phosphate of potash. The mean average composition of the ash of the potato is shown in the following table:[1]
Potash (K_{2}O), 60.37 percent
Soda (Na_{2}O), 2.62 "
Lime (CaO), 2.57 "
- ↑ Maercker, "Handbuch der Spiritusfabrikation," p. 99.
