Grain mill products

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1. GENERAL DESCRIPTION:


1. General Flowsheet of grain mill products


2. Description of techniques, methods and equipment
(BAT for Food, Drink and Milk Industries, June 2005)

There are a number of cereals important as food sources. These include wheat, barley, maize, oats, rye and rice. The main operations associated with flour milling are cleaning, conditioning, breaking, scalping, purification, reduction and dressing. The incoming grain is transferred to bulk silos prior to further processing. Gas or heat treatment may be applied to prevent insect infestation. The grain is first washed by passing through a series of screening, scouring, brushing and aspiration operations. These processes remove extraneous matter such as other cereals, stones, metal contaminants, chaff, loosened bran layers, seeds and dust. After washing, the grain is conditioned to optimise the milling process. This involves dampening the grain by the measured addition of water, which immediately binds the kernels. Conditioning may be made by using steam. Conditioning has a number of functions, such as toughening the bran, and thereby improves the separation of the bran from the endosperm, allowing the endosperm to be reduced more effectively in subsequent stages of the process. The conditioned grain enters the break system of the mill, which consists of pairs of corrugated rollers which revolve in opposite directions and at different speeds. Five sets of break operations are common, with the aperture gradually decreasing and the corrugation becoming finer between subsequent sets. The grain is split by the break-rollers and the endosperm is scraped from the bran. A screening operation known as scalping or grading is carried out after each break-roller. The semolina or middlings are then transferred onto reduction rollers, which are smooth and whose purpose is to crush the endosperm, As in the break section of the mill, there are a series of rollers and screening operations, so that flour is screened off whilst the coarser endosperm, retained on the sieves, passes to another set of reduction rollers to be further reduced in size. At the end of the reduction process, most of the endosperm will have been converted to flour, the coarse bran will have been removed and there will be a third stream of endosperm consisting of material containing fine bran which cannot be practically separated. There could be as many as 12 reduction stages in the process. Flour is normally passed over a final redresser at the end of the milling process or after bulk storage to remove any residual foreign bodies. Flour may be dried and classified by sieves into fractions.


3. Temperature ranges and other parameters (table)


4. Benchmark data


2. NEW TECHNOLOGIES:


a) Changes in the process


b) Changes in the energy distribution system


c) Changes in the heat supply system


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