Open main menu

Page:Popular Science Monthly Volume 19.djvu/265

This page has been proofread, but needs to be validated.
253
GLUCOSE AND GRAPE-SUGAR.

trade have optical and chemical properties quite different from many other substances bearing the same name. I shall use the words in the signification explained above.

Properties of Glucose.—Glucose is a thick, tenacious sirup, almost colorless, or of a yellowish tint. It has an average specific gravity, at 20° C., of 1·412. That which is made for summer consumption is a little denser than that manufactured for winter use. This sirup is so thick that, in the winter, it is quite difficult to pour it from one vessel to another.

The sweetness of glucose—i. e., the intensity of the impression it makes on the nerves of taste—varies greatly with different specimens. Some kinds approach in intensity the sweetness of cane-sugar, while others seem to act slowly and feebly. It has been shown that the degree of sweetness depends on the extent of the chemical changes which go on in the conversion of starch into sugar. When the process of conversion is stopped as soon as the starch has disappeared, the resulting glucose has a maximum sweetness.[1] The color of glucose depends on the thorough washing of the substance, during the process of manufacture, through animal charcoal, and lowness of temperature at which it is evaporated, and rapidity of evaporation. The methods of securing these conditions will be described further on.

There is one variety of glucose which is made for confectioners' use, which is much thicker and denser than that just described. Its specific gravity may reach 1·440, but it has no tendency to become hard and solid, like the so-called grape-sugar.

The grape-sugar made from corn-starch, when well made, is pure white in color when first made, but has a tendency to assume a yellowish tint when old. It is hard and brittle, does not usually take on a visible crystalline structure, and is less soluble in water than cane-sugar. Perhaps it would be more accurate to say that it dissolves more slowly, since both cane- and grape-sugar dissolve in all proportions in hot water. I have found its specific gravity to be as high as 1·6. It is much less sweet to the taste than glucose, and a faint bitter after-taste is to be perceived.

Uses of Glucose and Grape-Sugar.—Glucose is used chiefly for the manufacture of table-sirups, candies, as food for bees, for brewing, and for artificial honey.

It is impossible at present to get any reliable statistics concerning the amount of glucose used in beer-making. The brewers themselves try to keep its use a secret, since it is quite common to proclaim that beer is made from barley and hops alone, although this is rarely the case. Dealers and manufacturers are likewise reticent when approached on this subject, since it is but natural for them to wish to protect the interests of their patrons. We shall not go far wrong, however, when

  1. See paper read by the author at the Boston meeting of the American Association for the Advancement of Science.