Wet-Milling Operations

Historically, the use of wheat starch by the ancient Egyptians as an adhesive of papyrus and as an aid to harden the cloth material that covered the mummies is well known. A procedure for starch production was given in some detail in a Roman treatise by Cato in about 184 bc. Briefly, the grain was steeped in water for 10 days, pressed and mixed with fresh water, and the resulting slurry was filtered on a linen cloth. The filtrate, rich in starch, was allowed to settle, washed with water, and solar dehydrated (Whistler et al. 1984). The industrial production of wheat starch started in England in the 17th century and soon reached the United States. The first American wheat starch processing plant was established in New York around 1807. Nearly 40 years later, the same plant started to process maize starch. 

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In recent years, several wet milling operations have been initiated with obvious advantages in dust control and potential advantages in the separation of mineral contaminants from the fiber product. On the other hand, large-scale industrial wet classification methods are not in use at present. 

Extraction of Bertrandite. Bertrandite-containing tuff from the Spor Mountain deposits is wet milled to provide a thixotropic, pumpable slurry of below 840 p.m (—20 mesh) particles. This slurry is leached with sulfuric acid at temperatures near the boiling point. The resulting beryUium sulfate [13510-49-1] solution is separated from unreacted soflds by countercurrent decantation thickener operations. The solution contains 0.4—0.7 g/L Be, 4.7 g/L Al, 3—5 g/L Mg, and 1.5 g/L Fe, plus minor impurities including uranium [7440-61-1/, rare earths, zirconium [7440-67-7] titanium [7440-32-6] and zinc [7440-66-6]. Water conservation practices are essential in semiarid Utah, so the wash water introduced in the countercurrent decantation separation of beryUium solutions from soflds is utilized in the wet milling operation. 

The abundance of corn in North America at a relatively low and steady price, and its higher starch content, make it a much more attractive raw material for starch production than barley. Therefore, the potential success of a barley wet-milling operation which produces starch as a main product would rely on the value of other grain components such as (3-glucan, bran and protein. 

The ability to make corn syrups of high quality at a low cost depends upon having a supply of low-cost, high-purity starch. The com wet-milling operation is very efficient in its separation of corn into its constituent parts of starch, water-soluble materials, protein-fiber-rich materials, and corn oil at high yield and low operating costs. 

This also implies that the main mechanism for crystal breakage is individual crystal breakage in the cavitation field rather than particle-particle interaction, which is more common for most wet-milling operations. The breakage constant of about 0.03 gm/hr per (gm/liter, watt) was found to hold for a number of small molecule organic compounds tested in the fluidized bed crystallizer system. 

Particulate Matter (PM) Emission Factors for Corn Wet Milling Operations... 

Vibrating screens can be used for the separation of oversize material, which is then returned to the mill. Air cyclones have been used for classification operations after dry milling and their counterparts, hydrocyclones, are now coming into more frequent use as classifiers in conjunction with wet milling operations. 

Type 2 biorefineries differ from the first type by the number of products. A typical example is the production of starch, ethanol and lactic acid together with high fructose syrup, corn syrup, corn oil and com meal from corn wet mill operations. A more recent example that has been suggested is the use of citrus waste, such as orange peel (Figure 1.3). ... 

FIGURE 8.2 Equipment commonly used in wet-milling operations, (a) Disc-attrition mill, (b) Hydrocyclone (courtesy of American Association of Cereal Chemists). 

What are the three main functions of sulfur dioxide in wet-milling operations Why does the lactic acid generated by Lactobacillus act synergisti-cally with the sulfur dioxide ... 

FIGURE 8.2 Equipment commonly used in wet-milling operations.228... 

Potential applications of membrane processes in cereal production are in the treatment of stillage, in com wet milling operations, evaporation of steep water, concentration of dilute sweet waters, and in polishing of reverse osmosis permeate and evaporator overheads. Com proteins can be recovered from stillage solubles of dry milled fractions of com, grits, flour, degerminated meal, etc. by reverse osmosis. 

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