The cane is generally ripe for harvest at from twelve to sixteen months' growth. It is cut close to the round iust before its flowerinz time. beinE then heaviest in juice. The stubble develops new cane, the plants thus continuing, if so permitted, for several years. As however they gradually become weaker, it is customary to plow the stubble out after the second, third or fourth cutting—according to the strength of the soil—and to plant new slips.
The tops are sliced off the cane immediately after cutting and -the leaves stripped, only the denuded stalks being transported to the mills. An average analysis of high grade stalks in this condition shows about 72% water, 18% sugar and 10% woody and vegetable matter.
The Manufacture of Raw Sugar and Sugar Refining.
Two different processes are in use for extracting cane juice—"milling" and "dif fusion." The former is the "old" way, but it is still the one most generally employed, except in a few localities particularly suited to the diffusion method. "Diffusion" is used exclusively in treatment of the sugar-beet.
By the Milling Process, the stalks are unloaded from cars or wagons in huge bundles, often weighing five tons or more, into a "hopper," or onto a "carrier," which transports them to a "shredding" machine which tears the cane to shreds, or a "crusher" which crushes the hard rinds. They go next to the roller mills. The first mill extracts probably 60% of the juice. The "bagasse," as the crushed stalks are called, is then sprayed with water and put through a second, and again, after macera tion or saturation, through a third mill—after which the stalks are consumed as fuel in furnaces specially designed to utilize them.
The Diffusion Process recognizes the fact that in both cane and beet sugar juice there are two distinct substances—one that crystallizes and becomes sugar, and another that is gummy and will not crystallize. Crushing the cane in the mill extracts both together and the entire product must be treated and separated afterwards. Dif fusion takes out little except crystallizable juice, thus obtaining a liquid that gives a maximum of sugar and a minimum of syrup.
For the Diffusion process, the cane-stalks are sliced thin by cutting machines. The beets may either be similarly sliced, or crushed into pulp. The "chips" or pulp go to a series of large tanks called "diffusers" or "cells," where steam or water satura tion extracts the sucrose, the liquid being forced from one tank to the other, from those containing the partially exhausted chips to those filled with fresh chips.
The juice obtained by either process is of a sweetish taste and the appearance of sweet cider. It is pumped into tanks called "defecators," where it is first treated with
milk of lime and carbon-dioxide, to remove impurities. It then commonly undergoes two or three other purifying processes, by evaporation, through filters, etc., before it is ready for the multiple vacuum boilers, where it is condensed to syrup, and the vacuum pans, where it forms into crystals.
Next comes the separation of proportion of uncrystallizable syrup is mixed with the crystals. This is now generally accomplished by centrifugal machines —a wide-sided, cylinder-shaped basket of fine mesh is revolved at high speed inside an iron casing, and the syrup is ejected by the action into the casing, whence it drains into a receiver. The "cured" sugar left is known as Centrifugal, or "Raw," sugar, or locally as "Brown Sugar." The syrup of the cane product is shipped as Molasses. When the centrifugal process is not used, the Raw Sugar is known as Muscovado.
Molasses Sugar is that obtained by further boiling of the molasses. The uncrystallized resi due of this process is known as "Black-strap." It is frequently marketed as "molasses," but is an inferior article.
Practically all of the sugar imported into the United States—whether beet sugar from Eu rope or cane sugar from Cuba, the Dutch East Indies or Hawaii (the three chief sources), or elsewhere, comes in as Raw Sugar to be refined here, being graded in the custom-house according to its response to the polari scope test (see POLARISCOPE) . In refining, it is melted, passed through cloth filters to remove impurities and then through animal-charcoal filters to abstract all coloring matter. The clear syrup thus obtained is next boiled in a series of vacuum pans to crystallization. At this point, the process varies according to the market size of the sugar to be produced. For Granulated or Powdered sugar comes a further turbining, etc., and grinding to the desired size. Confec tioner's Sugar is powdered sugar ground especi ally fine. For Cut or Tablet, or "Lump," sugar, the melted product is run into frames divided into compartments about an inch wide, the frames after cooling being placed in turbines, where brisk revolving brings out the "first" syrup. A cleansing liquid is then added and further prolonged revolving brings out the "last" syrup. Next comes the drying in the ovens and, finally, the bars are cut or broken by special machinery into the desired size. The syrup yielded in these processes is again melted and further refined into sugar.