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Extraction of Sugar by Diffusion
The first step when the beets enter the factory is to remove any soil which is clinging to the beet. This is accomplished by spraying the beets
with high-pressure water sprays as well as passing the beet through a series of cylindrical tumble washers and rock catchers which will catch
and rocks or large dirt clumps that could damage equipment and would dull the slicing knives.
The next step in the “diffusion” process is slicing. In order to extract the soluble materials from the insoluble materials in the sugarbeet
we must first expose a maximum of surface area of the sugarbeets to the extracting solution (hot water). This is done by slicing the sugarbeets
into thin rectangular strips called “cossettes”, which resemble shoestring potatoes. This is done in large drum slicers, a type of industrial
grater, set with several pairs of rotating opposed groove knives.
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Removing soil from beets
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The cossettes are then conveyed across a weightometer, which feeds back information that controls the rate of slicer activity, and into the
cossette mixer. Here the cossettes are scalded with hot juice to sterilize them and to break down the cell walls in preparation for extraction
of the juice, and then pumped to two diffusers. The two diffusers used at SMBSC, both counter current mixing devices, are called tower
diffusers, each rated at 8,000 metric tons capacity per day (combined capacity of 17,600 short tons). Hot water is introduced at one end of the
diffusers and the cossettes at the other. The cossettes are propelled upward by a large, vertical screw conveyor.
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Slicing beets into Cossettes
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The purpose of the counter current design is for the cossettes to continuously come in contact with water which has a lower sugar content than
that left in the cossettes as the cossettes continue to lose sugar. What actually happens is a complex process involving osmosis, diffusion, and
active transport through and between denatured and ruptured beet cells and beet cell membranes, and the concentration gradients of the water
flowing in the opposite direction. What is important is that out of the opposite end of the diffuser from which they entered, come nearly sugarless
cossettes. Out of the end from which the cossettes entered, and opposite where the hot water entered, emerges the sugar extracted from the cossettes
contained in a “raw juice” which also contains many other soluble beet materials in addition to the sugar, all dissolved in the hot water.
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Diffusers
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