Wheat is one of the world’s most consumed cereal grains. It comes from a type of grass (Triticum) that is grown in countless varieties worldwide. Bread wheat, or common wheat, is the primary species. Several other closely related species include durum, spelt, emmer, einkorn, and Khorasan wheat. White and whole-wheat flour are key ingredients in baked goods, such as bread. Other wheat-based foods include pasta, noodles, semolina, bulgur, and couscous. Wheat is highly controversial because it contains a protein called gluten, which can trigger a harmful immune response in predisposed individuals. However, for people who tolerate it, whole-grain wheat can be a rich source of various antioxidants, vitamins, minerals, and fiber. Milling is the process by which cereal grains are ground into flour. The milling of Wheat consists in the separation of bran and germ from the endosperm and reduction of endosperm to fine flour. Various steps are involved in making the wheat flour.
The traditional procedure for milling wheat in India has been stone grinding to obtain whole wheat flour. This method results in 90-95% extraction rate flour which retains almost all the nutrients of the grain while simultaneously eliminating that part of the grain which is most indigestible like cellulose and phytic acid which binds and carries away minerals.
In modern milling, the wheat is subjected to cleaning to remove various types of impurities together with damaged kernels.
Following are the steps involved in wheat milling process-
- Grain Cleaning / Vibrating Screen: Grain is removed of various types of impurities together with damaged, shrunken and broken kernels which are collectively known as screenings. This removes bits of straw and other coarse materials and second screen removes foreign materials like seeds.
- Aspirator: It lifts off lighter impurities in the wheat. The stream of grain is directed across screens while air sucks off the dust and lighter.
- Disc separator: After the aspirator it moves into a disc separator consisting of discs revolving on a horizontal axis. The surface of the discs indented to catch individual grains of wheat but reject larger of smaller material.
- Scourer: The wheat then moves into the scourer, a machine in which beaters attached to a central shaft throw the wheat violently against the surrounding drum, buffing each kernel and breaking off the kernel hairs.
- Magnetic Separator: The stream of wheat next passes over a magnetic separator that pulls out iron and steel particles contaminated during harvesting.
- Washer stoner: high-speed rotators spin the wheat in the water bath. Excess water is thrown out by centrifugal force. Stones drop to the bottom and are removed. Lighter material float off leaving only the clean wheat.
- Tempering: Wheat is tempered, before the start of grinding, the process in which moisture is added. Tempering aids in separation of the bran from the endosperm and helps to provide constant controlled amount of moisture and temperature throughout milling. The percentage of moisture, length of soaking, time and temperature are three important factors in tempering with different requirement in soft, medium and hard wheat.
- Entoleter: Discs revolving at high speed in the scourer aspirator hurl the wheat against finger like pins. The impact cracks down any unsound kernel which is rejected.
- Grinding bin: The “first break” rolls of a mill and are corrugated rather than smooth, break into coarse particles.
- Sifter: The broken particles of wheat and bran go into a box like sifter where they are shaken through a series of cloth or screens to separate larger from the smaller particles. Larger particles are shaken off from the top by leaving the final flour to shift towards the bottom.
- Purifier: The top fractions and particles of endosperm graded by size are carried to separate purifiers. In a purifier a controlled flow of air lifts off bran particles while cloth screen separates and grade coarse fractions by size and qualities.
- The down purifier: Four or five additional break rolls with successively final corrugations and each followed by a sifter are usually used to rework the coarse stock from the sifter and reduce the wheat particles granular middling’s as free from bran as possible. Sifters, purifiers and rollers reduces wheat until the maximum amount of flour (72.0%) is separated.
Milling is a unit operation that transforms solid particles into smaller ones by applying forces such as shear, compression, friction, collision or impact. Milling processes can be used for making flour or for extracting gluten and starch (wet milling) from grains and cereals. In the food industry, raw materials, flours and intermediate products must often undergo milling or grinding for size reduction. Wheat is one of the cheapest and most nutritious crops. It is widely grown and is produced in abundance that is why it is used as staple food in most parts of India and the world. Clean, dry grains have to be milled to flour before further processing and consumption. The whole grain can be milled to leave just the endosperm for white flour. The products of this are bran and germ. The whole grain is a concentrated source of vitamins, minerals, and protein.
- Slide 1 (iaom-mea.com)
- flour | Production, Types, & Facts | Britannica
- Wheat Milling (cerealsdb.uk.net)
- wheat milling process – Google Search