SUGAR, HONEY, AND MAPLE

The Production and Use of Sugarcane

L. F. Martin.

Sugarcane and sugar beets have long reigned supreme as providers of sugar, an essential energy food. Sugarcane furnishes almost three-fourths of the world's supply. Many plants contain sucrose, but from none can it be produced as abundantly and cheaply in a highly purified form as from sugarcane. Besides the sugar, cane yields fiber, a mixture of some sucrose with other sugars in molasses, an industrially important acid, and a valuable wax. These are being recovered in some places and applied profitably in making useful byproducts.

Sugar itself intrigues chemists more and more as the cheapest and most abundant pure organic chemical available to industry. Its use in plastics and other synthetic chemicals is developing. Research is pointing the way to improvements in growing and processing the crop and to new applications and greater returns from utilization of every part of the cane.

Sugarcane can excel all other plants as a converter of the sun's energy and the carbon dioxide and water of the air into energy food and fiber. All around the world, wherever soil conditions and semitropical or subtropical climate combine to favor its growth, sugarcane has established itself as a major crop. From its homeland in India it traveled east and west until it reached the West Indies with Columbus. Thence it came to the French colony of Louisiana and later to Florida. We are concerned primarily with the industry in those two areas and in Hawaii and Puerto Rico.

The United States, with its high standard of living, is the world's largest consumer of sugar, but we grow only a small proportion of our total requirements. Unlike many other major commodities, sugar is not produced in surplus on American soil. In normal Times there is no difficulty in obtaining the extra quantities from abroad, but in every crisis domestic production has been taxed to the utmost to meet our minimum requirements.

THE DOMESTIC cane-sugar industry is experiencing one of those recurrent periods of readjustments that have marked its progress during more than 150 years and have necessitated continuous effort in surmounting obstacles, technical and economic. Facing new situations and problems is no new experience to men in this industry. It met one challenge in the 1920's, when, having adjusted itself to the return to normalcy after the First World War, mosaic disease nearly destroyed it. Disaster was averted by the introduction of resistant varieties of sugarcane from the East Indies, which was followed by a program of breeding improved canes still more resistant to the disease. We expect that the present challenge will also bring forth major improvements in production and processing.

Today a major concern is the conversion to mechanical harvesting, a goal toward which there had been a gradual evolution but which was abruptly forced upon the industry almost completely by the scarcity of labor during the Second World War. There is general agreement as to the desirability of handling the crop mechanically, but the mechanization effected since 1945 has posed problems requiring ingenuity and intensive research for solution.

If the 1950 costs of producing the crop are to be justified, every substance of value, as well as every ounce of sugar, must be extracted. That has called for reappraisal of the entire process of grinding and manufacture into sugar and molasses, and for revaluing every fraction of the cane for application in producing useful byproducts.

THE PROCESS of producing pure white crystalline sugar from cane is almost invariably carried out in two stages recovery of crude or raw sugar and its refining. Both are essentially simple, traditional procedures. Innovations have increased efficiency, reduced costs, and improved every step of the operations.

To produce raw sugar, the cane is crushed in a series of roller mills, with the addition of water between crushings. The added water serves to dissolve more of the sugar, which is pressed out in other mills. In that way as much sugar as possible is extracted. The somewhat diluted juice thus obtained is thoroughly mixed and a measured amount of lime is added. The lime combines principally with phosphate in the juice and, by altering its acidity, forms a precipitate when it is heated, which removes many impurities. After adjusting the amount of lime and heating to the boiling point, the juice is passed to large vessels arranged to hasten the settling of the precipitated impurities, which are drawn from the bottom while clear juice passes from the top. In most modern mills, the sludge of impurities goes to continuous filters and is washed with water, so that a maximum proportion of the sugar trapped in it is recovered and returned with the clear juice to the evaporators.

Finally, the juice is evaporated to a sirup. That is done under vacuum to prevent darkening and decomposition, which would result from the high temperatures necessary if open kettles were still used as in earlier days. The raw sugar can be crystallized from the concentrated sirup in vacuum vessels heated by steam. Molasses is thrown out of the mass of crystals by spinning in centrifugal machines, from which the brown raw sugar is then discharged.

In some factories the crude product goes on to the refining process. More commonly, however, the raw sugar is shipped to large central refineries, which have much greater operating capacity than most sugar mills. It is redissolved at the refinery. The sirup is clarified. Impurities are filtered out. The color is removed by carbon, most commonly bone char, or bone black. The heated sirup is passed through towers charged with the decolorizing bone char; the sirup, now water-white, goes to evaporators and vacuum pans much like those of the raw-sugar factory. It is concentrated and white sugar is crystallized and separated from the sirup in centrifugals. After drying in large rotary driers, in which the sugar crystals are poured through a stream of filtered and heated air, the product is screened and packaged.

Every step in the process requires precise technical control and depends on the latest innovations of chemical and engineering science.

The most difficult step is the clarification, in which lime is added and conditions are adjusted to effect the removal of plant coloring matter and other impurities as completely and rapidly as possible. The success of subsequent operations in crystallizing the sugar and the yield obtained depend almost entirely on the effectiveness of the clarification. Sugarcane of different Varieties and grown and harvested under different conditions is not uniform, and the juice varies in composition and quality as grinding proceeds through the harvesting season. Control of the clarification process must be adjusted continually to meet varying requirements.

AFTER RECOVERING from the mosaic epidemic of the 1920's, the Louisiana cane-sugar industry has been a dynamic one. Before 1926, practically the entire crop consisted of two varieties of cane, Louisiana purple and D-74, obtained from Demarara. They were extremely susceptible to mosaic, and within about 3 years had to be replaced completely by the P. O. J. ( initials of the name of the East Java Experiment Station) canes from Java. New varieties have been released on an average of about one a year-24 since 1924. Consequently, between 1929 and 1939, nearly all the P. O. J. canes were displaced by varieties from Coimbatore, India, designated as "Co." varieties. The Co. canes, in turn, have been almost completely replaced by varieties from the Department's breeding station at Canal Point, Fla. They now occupy about 85 percent of the total cane acreage in Louisiana. Indications are that they will be displaced by other improved and more resistant varieties in the coming decade.