Popular Science Monthly/Volume 19/June 1881/Glucose and Grape-Sugar
|GLUCOSE AND GRAPE-SUGAR.|
By Professor HARVEY W. WILEY.
THE manufacture of sirup and sugar from corn-starch is an industry which, in this country, is scarcely a dozen years old, and yet it is one of no inconsiderable magnitude. On August 1, 1880, ten glucose-factories were in operation in the United States, consuming daily about twenty thousand bushels of corn. These, with their several capacities, are as follows:
|Higher, St. Louis||1,000||"|
|Peoria Refinery, Peoria||2,500||"|
|Peoria Grape-sugar, Peoria||850||"|
|Davenport, Davenport, Iowa||1,500||"|
|Freeport, Freeport, Illinois||1,500||"|
|Sagetown, Sagetown, Illinois||250||"|
At that time, also, there were in process of construction nine factories, with a total capacity of twenty-two thousand bushels daily.
At the same time additional machinery was in process of erection in the two Peoria factories, which increased their capacity two thousand and twenty-five hundred bushels, respectively.
The new factories were building in—
We may safely assume that at the present time one half of these new factories are in running order. The total daily consumption of corn, therefore, for sugar-and sirup-making, is not far from thirty-five thousand bushels.
Eleven million bushels of corn during the present year will be used for this purpose, and every indication leads us to believe that the amount will be doubled in 1882.
The capital invested in this sugar industry is likewise no inconsiderable one. Taking the large and small establishments together, each thousand bushels of daily capacity represents sixty thousand dollars of capital. Over two million dollars are therefore actively employed in the glucose-works. The number of men employed amounts to about sixty for each thousand bushels capacity, making a total of twenty-one hundred. On account of the nature of the process of manufacture, the mills are run night and day, and work is not entirely suspended on Sunday.
To avoid confusion of ideas, the following statements seem necessary: The word glucose, in this country, is employed among dealers to designate exclusively the thick sirup which is made from cornstarch. On the other hand, grape-sugar is applied to the solid product obtained from the same source. The glucose and grape-sugar of the 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. 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 we say that the amount of glucose used by brewers is by no means small, and that the quantity is constantly increasing. I do not know any reason why its moderate use should injure the quality of the beer.
Bees eat glucose with the greatest avidity, or, rather, they act as funnels by which the glucose is poured into the comb. For it is quite true that honey made by bees which have free access to glucose differs scarcely at all from the glucose itself. But the quantity of honey which a bee will store away when fed on glucose is truly wonderful. This gluttony, however, rapidly undermines the apiarian constitution, and the bee rarely lives to enjoy the fruits of its apparent good fortune. In commercial honey, which is entirely free from bee mediation, the comb is made of paraffine, and filled with pure glucose by appropriate machinery. This honey, for whiteness and beauty, rivals the celebrated real white-clover honey of Vermont, but can be sold at an immense profit at one half the price.
All soft candies, waxes, and taffies, and a large proportion of stick candies and caramels, are made of glucose. Very often a little cane sugar is mixed with the glucose, in order to give a sweeter taste to the candies, but the amount of this is made as small as possible. As has been stated above, the glucose which is used in confections is evaporated nearer to dryness than that which is used for sirups. In such glucoses I have found the percentage of water to be as low as 6·37. Such a product is almost thick enough for "taffy" without any further concentration.
A very large percentage of all the glucose made is used for the manufacture of table-sirups. The process of manufacture is a very simple one:
The glucose is mixed with some kind of cane-sugar sirup until the tint reaches a certain standard. The amount of cane-sugar sirup required varies from three to ten per cent., according to circumstances. These sirups are graded A, B, C, etc., the tint growing deeper with each succeeding letter.
When these sirups are sent into the shops, they are sold to consumers under such altisonant names as "Maple Drip," "Bon Ton," "Upper Ten," "Magnolia," "Extra Choice," "Golden Drip," "White Loaf Drip," etc. Dealers tell me that these sirups, by their cheapness and excellence, have driven all the others out of the market. So much is this the case that it is no longer proper to call glucose the "coming sirup." It is the sirup which has already come.
In addition to the uses above mentioned, small quantities of glucose are used by vinegar-makers, tobacconists, wine-makers, distillers, mucilage-makers, and perhaps for some other purposes.
Grape-sugar is also used for many of the purposes enumerated above, but chiefly for the adulteration of other sugars. When it is reduced to fine powder, it can be mixed with cane-sugar in any proportions, without altering its appearance. Since the grape-sugar costs less than half the price of cane-sugar, this adulteration proves immensely profitable. The presence of grape-sugar in table-sugars can be approximately determined by several simple tests. When placed on the tongue, the bitter after-taste, already spoken of, may be detected. If spread in a thin layer on a piece of glass, and treated with a little water, the cane-sugar granules dissolve first, and the grape-sugar is left as a flocculent mass. With the microscope, its particles can be detected by the absence of all crystalline structure. Its exact quantity can only be determined by the polariscope. This is hardly a proper place to describe how this is done.
From the best information I can obtain, it appears that the cost of manufacture of glucose and grape-sugar is about one cent a pound. From twenty-six to thirty-two pounds are made from a bushel of corn. It is sold by the manufactories at three to four cents per pound. In the West the price of corn during the last year has averaged a little over thirty cents per bushel. It thus appears that the manufacture of glucose is a profitable industry.
I shall attempt here no detailed statement of the method of manufacture, but give only such an outline as may interest those who like to know how the things on their tables are prepared. The corn is first soaked for two or three days in warm water, and is then ground on specially prepared stones with a stream of water. The meal is next passed into a trough, the bottom of which is made of fine bolting-cloth. Here the starch is washed through, and led to large tanks, where it is allowed to settle. It is next beaten up with caustic soda to separate the gluten, and the starch is again allowed to settle in long, shallow troughs. The starch, washed from all adhering alkali, is next beaten up with water into a cream, and conducted into the converting-tubs. These tubs are supplied with coils of copper steam-piping and are made of wood. Here the starch cream is treated with dilute sulphuric acid, and steam is allowed to bubble up through the mixture from small holes in the copper pipes. This process of conversion, which is called "open conversion," is completed in about two hours.
Another method is called "close conversion." The substances are inclosed in stout copper cylinders, and subjected to the action of superheated steam. This process occupies about fifteen minutes.
The conversion is also accomplished sometimes by fermentation. This requires a much longer time. The greater part of it, however, is carried on by the method first named.
After conversion the acid is neutralized by marble-dust and animal charcoal. Since the sulphate of calcium, which is formed in this operation, is slightly soluble in water, carbonate of barium has been used instead of marble-dust. Its use, however, has not become general.
After neutralization the liquid is filtered through cloth and animal charcoal, and is then conveyed to the vacuum-pan. Here it is evaporated, at as low a temperature as possible, to the required concentration. If grape-sugar is to be made, the process of conversion is not stopped as soon as the starch has disappeared, but is carried on still further to a point which can only be determined by trial. After concentration it is conveyed into tanks, where the process of solidification begins and continues for several days.
Glucose, on the other hand, will not harden, whatever the degree of concentration may be, or, at least, if it do so, only partially and after many months.
The habit of bleaching both glucose and grape-sugar by means of sulphurous acid is sometimes practiced, but is reprehensible. By the oxidation of the sulphurous acid, free sulphuric acid is likely to occur in the finished product.
Glucose and grape-sugar are mixtures of several chemical substances. Starch, which is composed of six atoms of carbon, ten of hydrogen, and five of oxygen, when subjected to the action of dilute sulphuric acid, appears to undergo a molecular condensation and hydration. Among the substances formed may be reckoned dextrine, glucose, and a substance isomeric with cane-sugar. This latter substance appears to be one of the early products of conversion, and this is the reason that the poorly converted glucoses are sweeter than the well converted. It is only after prolonged boiling with dilute acid that the product becomes chemically homogeneous, with a constitution which is probably represented by the symbol C6H12O6H2O.
Glucose presents several anomalies when examined with polarized light. Its highest rotatory power is found when it is made with the least possible amount of conversion—i. e., when the process of conversion is stopped as soon as the starch has disappeared. Continued boiling with dilute acid causes a gradual decrease of rotatory power. It is only after six to eight hours' heating to a temperature of 104° C. that a constant rotatory power is reached. This power is only about half that exhibited by the glucose as a maximum. This minimum rotatory power, however, is greater than that possessed by cane-sugar.
Glucose, like many other bodies, has the property of reducing a hot alkaline copper solution and separating the metal as a red sub-oxide. This power in glucose is always inversely as the rotating power. I have shown this fully and conclusively in the paper already referred to. The relation between reducing power and rotating power is a constant one, and hence the percentage of reducing power can be calculated from the polarimetric observations. This, however, is of more interest to the practical chemist than to the general reader, and I therefore pass it by.
The question of most practical importance is, "Is glucose a wholesome article of food?" I do not hesitate to answer this question in the affirmative, I mean by this, however, a glucose which is properly made. Such a glucose contains only a very little sulphuric acid and lime, not much more than good spring-water, and perhaps an almost infinitesimal trace of copper, so slight as only to be detected in a large quantity of the substance. I do not doubt but that glucoses have been sold which contain large quantities of free sulphuric acid and likewise other injurious ingredients. But these are due to carelessness in manufacture, and are not constituents of the genuine article. I have never found a glucose of this kind. Many of the impurities which have been imputed to glucose, really belong to the cane-sirups with which they have been mixed. These largely adulterated glucoses should always be looked upon with suspicion. The cane-sirups, which are used for this purpose, yield from three to five per cent. of ash, while the ash from a genuine glucose is so little as to be almost unweighable.
There is no reason to believe that a glucose or grape-sugar properly manufactured is any less wholesome than cane or maple-sugar. Corn, the new American king, now supplies us with bread, meat, and sugar, which we need, as well as with the whisky which we could do without.
- See paper read by the author at the Boston meeting of the American Association for the Advancement of Science.