Starch From Wheat

by CECIL T. LANGFORD and CARL E. RIST

STARCH is one of the most important industrial commodities derived from agricultural crops. Just before the war the annual domestic production was nearly 4 billion pounds. More than 98 percent of it was produced from corn, and only about 1 percent from wheat. The almost complete reliance on corn as a raw material has been due to the normally higher price of wheat as compared with corn. Another factor is the good return of oil as a byproduct from the milling of corn for starch.

Shortly after we entered the war, when large quantities of corn were being diverted to livestock production and industrial alcohol, it became apparent that a starch shortage would ensue. Because of the scarcity of cane and beet sugar, it was also evident that the production of corn sugar and sirup would be inadequate to meet the increasing demand for sweetening agents.

Accordingly, investigations were undertaken at the Northern Regional Research Laboratory in Peoria, Ill., for working out new processes whereby starch could be produced from wheat and wheat flour, both of which were plentiful then. There were two necessary restrictions : The processes should require a minimum of equipment for new installation, and, if possible, they should be adaptable to existing available plants. As a result of the work, two processes were developed for producing wheat starch for conversion into sirup, sugar, or industrial alcohol.

The use of wheat flour as a raw material for the production of starch had several advantages. The ample flour-milling capacity available permitted the use of existing equipment to remove more than 25 percent of the starch-poor constituents in the form of bran and other feed products. This initial purification saved the installation expense of hard-to-get new equipment in starch-processing plants. A rather ample supply of clear grade flour also was available, a byproduct of milling wheat for other products. The two major constituents of wheat flour are starch and gluten. Accepting wheat flour as a raw material, the problem was to develop a process that would give a separation of the two in relatively pure form.

Starch and Gluten From Wheat Flour

A successful process was developed at the Northern Regional Research Laboratory that required no extensive installation of equipment. It was called the batter process because it involved mixing flour and water to give an elastic but free-flowing batter. The basic principle involved is readily understood by anyone who has chewed wheat grain. Slow mastication leaves in the mouth a gummy, chewy mass of gluten a farm-made chewing gum of years past.

One part of flour and about one and one-fourth parts of warm water (depending on the type of flour and gluten content) are mixed. The batter, after thorough mixing for 10 to 20 minutes, should be quite smooth and free of lumps. Compared with the usual pancake batter, this is a stiff batter because it contains about one-third less water.

In the next step the batter is mechanically broken up in the presence of about 2 3/4 parts of cold water. The starch is quickly and almost completely washed out of the batter, and the gluten is left suspended in the slurry of starch and water in the form of lumps or curds. The gluten is separated by allowing the whole slurry to be drained or pumped onto a vibrating screen that has 60 to 80 meshes to the inch. The lumps of gluten collect into larger masses on the screen and fall off the end. The starch and the water that contains other flour solubles pass through the screen. The suspension of starch in water is usually called starch milk.

This starch milk, containing some fine fiber, soluble protein, and a small amount of fine gluten particles, may be used directly for fermentation into industrial alcohol. Without further purification, the starch milk may also be converted into glucose sirup or dextrose by being cooked in the presence of hydrochloric acid. The sirup and sugar produced by the use of the starch milk as it comes through the screen will not be of the highest quality. Unless extra-large quantities of decolorizing agents are used, the sirup and sugar will be slightly dark in color. Also, the protein contained in the sirup will cause it to become cloudy on long standing. To make the best refined sirup and sugar, the starch has to be purified by removing the protein and impurities in the starch milk.

Prime-quality starch is obtained by allowing the starch to settle out 01, starch tables. In large-scale practice, the tables are long troughs about 2 feet wide and 90 to 120 feet long. They are set on an inclined base, dropping about 5 inches from the head to the tail end. The settled starch is flushed off the tables by strong streams of water, collected in tanks, and finally filtered. Besides being used to prepare refined sirup and dextrose sugar, the purified starch may be dried and used for numerous other purposes. Sirup may also be made by the action of malt on either the crude-starch milk or the purified starch. The resulting product is either crude or refined malt sirup, depending on the purity of the raw material.

The crude gluten passing over the end of the mechanical screen contains 72 to 75 percent protein and about 20 percent starch on the dry basis. When this first crude gluten is washed again in fresh water, the protein content is easily raised to about 85 percent, and the starch content is reduced to about 10 percent on a moisture-free basis. Gluten containing up to 95 percent protein can be prepared by repeated washings in water.