Sorghum Sugar.

Botanical name: 


From an Inaugural Essay.

The different kinds of sorghum (Sorghum saccharatum), now under cultivation in the United States, are varieties and hybrids from two main groups; the one the Chinese sugar cane, or sorgho, or sorghe, from China and India, and the second the African sugar cane, or imphee from the south of Africa. As varieties of the first group, we have the regular sorghum, Honduras cane, honey top, sprangle top, etc. Of the second group the most important are, the Liberian imphees, white African, white mammoth, Iowa red top and wolf's tail. As hybrids, the early amber is the most common, early orange and a number of others. These hybrids need, as also their names indicate, a shorter time to attain maturity, and are therefore especially adapted for the more northern range, Wisconsin, Minnesota, etc., where the season is rather short; while the countries further south, with a longer season, have the advantage, that they can utilize both the early and late varieties, and thus be able to supply the mills for a longer time; besides that they also can utilize the other qualities, desirable in good cane, as saccharine richness, large percentage of juice, and large stalks. A rather sandy loam is said to be the most favorable soil for its cultivation.

The first seeds of the new sugar cane were brought to America in 1854 from France, where they had been imported from China only a few years previous. Not long afterwards also seeds of the African variety found their way over here. And now sorghum is to be found cultivated almost in all parts of the United States, where the climate is favorable to its growth; and it is said that where maize will thrive, sorghum also will.

Its principal use has, until lately, been confined to the mere production of syrup, as a very sweet, and to most persons, agreeable article of this kind may be prepared by means of quite inexpensive machinery. But the production of a cheap, marketable sugar from it, has, until the last three years, met with no success. Sugar has of course been produced from it long before this, but on account of inferior machinery and limited means it would not pay. It is also said that a fatty substance is contained in the juice of sorghum, which hindered the crystallization of the sugar, and necessitated another process than that used for the common sugar cane. The first sugar reported obtained from sorghum, was made by a farmer in Wisconsin (according to Prof. Carl Mohr). In 1858, J. S. Levering, a chemist of Philadelphia, received the gold medal from the United States Agricultural Society, as an acknowledgment for his successful and meritorious experiments in sugar making from sorghum ("Amer. Jour. Phar.," 1855. p. 182; 1858, p. 105). In spite of the publication of his process, no attempt was made to utilize it. Later, through the Commissioner of the Department of Agriculture at Washington, G. W. Le Due, a great deal was done in order to arouse the interest for it, that new experiments should be undertaken. Steward, a Pennsylvania chemist, also treated the subject, and showed at the Centennial Exhibition, in 1876, samples of sugar which he had obtained by his experiments. With still greater energy Dr. Collier, chemist of the Agricultural Department at Washington, took up the work, and of the results of his thorough investigations, he has given a minute account in his several reports, which has thrown much light on the subject.

At the same time, Prof. Swenson, of the University of Wisconsin, was occupied with investigations of the same kind, and when the United States government, through the Agricultural Department at Washington, offered a prize of $1,200 for the best method of treating sorghum cane, it was awarded to him.

Some New York capitalists, after having corresponded with Prof. Swenson and secured his service, determined to establish a sugar mill in some portion of the country, where the cane could be grown successfully and cheaply. The Arkansas river valley was decided upon, and in 1882 the mill was built at Hutchinson, Kansas. As an experiment some sugar was successfully made, already late, the same season. Last fall (1883), they made as an average 40 barrels of sugar and about 200 gallons of syrup a day. This was the first undertaking on a large scale, and as it proved a success, others have followed their example, and many more are likely to follow.

The process used in the above named mill I have not seen myself, but will give it as it has been described. The cane, having been examined by the chemist and found in the desirable ripe condition (when it contains most saccharose and least glucose), is cut, topped and hauled to the mill without stripping. Arrived there it is placed on a long endless belt, which acts as an elevator to carry it to the crusher, which consists of huge iron rollers. The cane is passed through this crusher at the rate of 25 tons per hour. The juice, as it runs from the rollers, passes into a large tank, from which it is pumped into the defecating room. Here it is run into six defecating pans, capable of holding three tons of juice each. In these are coils of copper tubing, through which steam is passed to heat the juice. To the lukewarm juice is then added milk of lime, until slightly alkaline, in order to neutralize the acids, which are always contained in it, and to coagulate the albuminous matter present. It is then heated as rapidly as possible to the boiling point, and the steam is shut off when the thick scum, which rises to the surface, begins to swell and break. After a few minutes the juice is skimmed, and it is again heated, this time to a quiet ebullition and again skimmed. This is repeated a few times, and the result is a very clear juice, almost free from sediment. From the defecating room the juice, containing 84 parts of water and 16 parts of sugar, passes to the evaporating pans, where it is boiled down to 54 parts of water and 46 parts of sugar, when it is called "semi-syrup." This passes into a small vacuum pan, and from there into the bone-black filters. These are six in number, and are each cylindrical in shape, four feet in diameter and 20 feet high. Here the syrup is decolorized and deodorized, after which it is pumped into the large vacuum pan. This is ovoid in shape, made of boiler iron, and looks like a huge retort. It is seven feet in diameter, nine feet high, and will hold more than 1,000 gallons. In this the semi-syrup boils at 70°C. under diminished pressure, instead of 110°C. in free air. This is a great advantage, as it is a well-established fact that high heat and much exposure to the air quickens the conversion of sacharose into invert sugar. From the vacuum pan the syrup is put into large iron wagons, which hold about 250 gallons each, and in them is run into the crystallizing room. This room is kept at a temperature of 55° C., and in it the syrup is allowed to stand for several days until it crystallizes. The "melado" as the syrup at this stage is called, is then run into the mixer. This is a long bar with fingers attached, the whole revolving in an iron box. In this the melado is thoroughly mixed and made ready for the last process. From the mixer the melado is run into the centrifugals. These, four in number, are tubular vessels about three feet in length and two feet high, open above and closed below. Each is lined with fine copper sieve, a space of perhaps two or three inches intervening between the sieve and the outer wall of the centrifugal. The centrifugals are set in motion at the rate of 2,000 revolutions per minute, and the melado is run into them, falling upon a revolving disk in the centre. From this the melado is thrown with great force against the side of the vessel, striking upon the copper sieve, which is also in rapid revolution. The force of the projection throws the syrup through the sieve, while the crystallized sugar remains behind, whitening the longer it "spins," as the process is called. It is generally allowed to spin about fifteen minutes, after which the raw sugar is taken out and put into barrels, and the process is completed. Each centrifugal is capable of spinning 200 lbs. of sugar in those fifteen minutes. Besides these details, the process has, of course, its secrets, which are also kept as such.

From the above-named factory I obtained a sample of sugar, of which I made an analysis, which shortly will be explained. In appearance the sugar looks very much like the common raw sugar of commerce. But in odor and taste it differs somewhat, as it has retained some of that peculiar sorghum flavor, which is not disagreeable, and in which place in common raw sugar is found a taste and smell of burnt sugar.

In my analysis of the sorghum sugar I found the following constituents:

Saccharose 92.00 per cent.
Glucose 4.50 per cent.
Moisture 1.50 per cent.
Ash 1.10 per cent.
Impurities 0.90 per cent.

The amount of saccharose was ascertained by the use of the Wilde polariscope, which as an average showed 92°. With the same instrument I examined samples of different sugars with the following results (The strength of the solutions was 10 grammes of sugar and water sufficient to make 100 cc.):

White rock candy polarized 100°
Yellow rock candy polarized 93°
Best granulated sugar polarized 99°
White A sugar polarized 94°
Common raw sugar polarized 84°
Sorghum sugar (4 experiments) 90°, 92°, 93°, 92°

Common raw sugar was also subjected to analysis for comparison:

Saccharose 84.00 per cent.
Glucose 11.80 per cent.
Moisture 2.50 per cent.
Ash 0.70 per cent.
Impurities 1.00 per cent.

The moisture and ash of granulated sugar was also ascertained and found to be respectively 0.55 and 0.44 per cent. This shows in reference to the moisture, that the more glucose contained in the sugar, the more moisture is absorbed. As to the sorghum sugar the comparison is very satisfactory, as it contains eight per cent. more saccharose than the common raw sugar, and only two per cent. less than the A sugar, which has gone through a refining process. This very satisfactory result is due to the improved machinery of which the vacuum pan and the centrifugals are the most important, and without which the idea of sugar making, from sorghum, at the present sugar prices, might be given up as almost hopeless. But as it is, sorghum sugar can compete with other sugars, both in price and quality.

The American Journal of Pharmacy, Vol. 56, 1884, was edited by John M. Maisch.