All modern varieties are derived from two standard types of "improved" sugar beet, namely, Vilmorin's Blanche Amelioree produced in France, and Klein Wanzleben produced in Germany. Although some varieties may contain over 20% of sucrose, the average sucrose-content is 16%, as compared with 13% for the sugar cane.
For the Chemistry of the Sugars, see articles : CARBOHYDRATES; GLUCOSE; and FRUCTOSE.
Formerly, white sugar could be produced only by the combined operations of the "raw sugar factory" and the "refinery." Raw sugars, made from cane and beet juices, contain about 96% of sucrose. Refined white sugars, made by further treatment of raw sugars, contain about 99.8% of sucrose. With progress in sugar technology, it became possible to produce white sugars, of high purity, from cane and beet juices by a direct process (not used in the refinery). They are termed "direct consumption sugars." Extraction of the Juice.—From the earliest times, the juice has been extracted by crushing the canes between rollers, and a simple form of mill consists of three horizontal rollers, one being placed above the other two (see one of the four mills shown in section in fig. 3). Slow rotary motion of the top-roller is trans mitted to each of the two lower rollers (front and back rollers) by toothed gearing, causing the three rollers to rotate at the same speed of 2 to 21 rev. per min. The canes are crushed between the top and front rollers, and again, between the top and back rollers; while the extracted juice flows down the surfaces of the two lower rollers and falls into a receiver below, whence it flows to a strainer and pump.
The modern cane-mill, fig. 3, is a combination of three or more of these mills, with mechanical transporters for carrying the crushed cane (megass or bagasse) from one mill to the next, and from the last mill to the furnaces, where it is used as fuel. In order to prepare a uniform and compact feed entering the first mill, the canes are first reduced to small pieces by passing through one or more machines, called knives, crushers and shredders. In
fig. 3, the first mill is preceded by a crusher, consisting of two rollers having interlocking teeth which cut the canes into short lengths, squeezing them and extracting much juice.
The heavy pressure applied by the mill-rollers is produced by hydraulic power acting on the sliding bearings of each top-roller, forcing these rollers vertically downwards upon the feed passing over the lower rollers. One top-roller may thus apply a pressure of over 5oo tons.
The extraction is greatly increased by spraying water upon the bagasse as it passes from one mill to the next, thus diluting the unextracted juice in the bagasse, and facilitating its extraction in the following mill. In fig. 3, water is sprayed upon the bagasse behind the third mill ; the very dilute juice extracted by the fourth is pumped to a spraying-pipe behind the second (see pipe-line and arrow) ; and the dilute juice extracted by the third mill is pumped to a spraying-pipe behind the first. The juice extracted by the crusher and first two mills flows to a tank from which it is pumped to another part of the factory. By this system of spray ing with water and dilute juice, the mill shown in fig. 3 will extract from 95 to 96% of the total sucrose in the canes. The addition of a shredder between the crusher and the first mill will increase the extraction to 97 or even 98%, according to the quantity of saturation water applied between the mills. A more powerful milling plant consists of two sets of knives, followed by a crusher, a shredder and five mills, and extracting about 99% of the sucrose in the canes.
The bagasse, leaving the last mill, contains about 45% water, 5o% fibre, and 2 to 4% unextracted sucrose. Under normal con ditions, no other fuel is required for steam production.
The extracted juice is a dark, opaque liquid, having an acid reaction. It contains from 12 to 16% of dissolved sucrose, and small percentages of glucose, fructose, organic acids, colouring matters, nitrogen compounds, pectin, gum and mineral matters. It also holds in suspension finely divided fibre, wax, clay and air-bubbles ; the last slowly rising to the surface, forming a thick white foam.