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Preparation of flour starts with the following unit operations;
I. Receiving; grains of one single proper variety are received. A random sample can be checked for the presence of extraneous material and quality of grains. The sample can be subjected to the moisture content determination and whether the grains are sprouted or not.
II. Cleaning; during the cleaning, impurities are removed which may include any foreign material. Reciprocating screws remove stones, chaff and other coarse or fine material. Then air current through aspirator remove lighter impurities. Magnetic separator, if provided, can pick up small nails, metal chips or iron objects. In a suitable washer, by the agitation action impurities sink at the bottom. It also helps to equalise the moisture level of the grains.
III. Conditioning; after washing, the moist wheat is conditioned for a predetermined time. During conditioning bran gets tough which helps its removal. Conditioning also mellows the endosperm which helps in the milling properly. Conditioning is done at 65oC for a holding time of 18 to 72 hours. the hard wheat?s retain about 90% moisture, while soft wheat 70%.
IV. Milling: the purpose of milling is to obtain maximum proportion of flour from the grain and to produce a precise specification of quality. Different types of wheat could be blended to obtain the flour of a particular specification.
Conditioned wheat passes through a set of break-rolls, which have two rolls with grooves moving at differential speeds in opposite direction from each other. The grooves are so designed and speed of break-rolls is so adjusted that wheat grain is broken only gradually.
A few wheat passes the first break-rolls, some bran is separated and lifted off by air currents. A small amount of flour is milled and separated.
Large chunks of grains are further directed to second set of break-rolls where similar process takes place till, finally, pieces of wheat kernel are almost devoid of bran.
The product so obtained is called semolina or suji. During the break-roll operation, some flour is produced. This comes from the centre of the kernel and has minimum of bran contamination. Although the protein in this flour is comparatively less, but quality is superior. This is called the patent flour. Flour of good condition should have a creamy white colour with pleasant smell.
V. Bleaching and maturing; sometimes bleaching is done to remove the yellow colour. The flour is bleached or matured, either chemically or naturally, by storing it for 10 to 15 days. The maturing process reduces the proteolytic enzyme activity. It improves the baking quality and modifies the gluten property.
VI. Enrichment; flour can then be enriched with thiamine, niacin, iron, calcium etc.
Effects on nutrient and disadvantages
• Many of the nutrients eliminated in the milling process, such as vitamin E, are crucial to good health.
• Milling removes the pericarp, aleurone layer and germ that are rich in nutrients
• Texture, and body are lost in milling
Titany answered the question on April 22, 2022 at 07:22