The story behind a loaf of bread
OLD AND NEW METHODS OF MILLING
In the mill, the grain passes through more than forty processes before it emerges as flour and bran.
|At the first stage of the milling process, the clean blended wheat passes between chilled iron rolls which revolve rapidly, one roll faster than the other. These first sets of rolls (known as the break rolls) have ridges or 'flutes' on them. The slower moving roll tends to hold the wheat while the faster one strikes the grain as it passes between them. They are set very delicately, so that as the wheat passes between them, they do not crush it, but shear it open in order to make the inner white floury portions of the wheat come away from their brown outer skins. If the wheat was merely crushed, the brown skins would break up into countless tiny fragments, and would mix with the white portions so thoroughly, and so finely, that they could never be separated properly. These skins would then discolour the flour badly and also spoil its baking qualities. Some of the white floury portions will have broken away||
cleanly from their brown outer skins, but other white portions will still have pieces of skin fastened firmly to them. Therefore the materials from the break rolls must be sorted out. The pieces of brown skin must be separated from the white portions, and some of the material must be sent back to the fluted rolls for further separation. This sorting out is done mainly by sifting the mixture of particles from the 'break' rolls; the mixture is first moved by elevators to the top of the mill.
There are several different types of sieving machine but usually only two kinds are used at this stage: first the 'plansifter' and then the 'purifier'. This is how they work.
Plansifters on Sifter Floor
|The plansifter is an arrangement of about a dozen large sieves, one below
the other-just like the floors of a tall building. The top sieve has the
coarsest mesh, the next not quite so coarse, and so on. These sieves are
all made to swing briskly by machinery - in fact they swing continuously
with a motion very like that of the ordinary sieve at home. The broken wheat
comes first onto the top sieve, and then through the others in turn, each
sieve helping to separate the material. The first sieves remove the bran
skins, which, because they still have flour particles adhering to them,
are returned to another milling machine for re-treatment. The finest sieves
are of silk, and these separate flour, which then starts on its way to the
flour-packing spout. The majority of particles are not of bran, of course,
but are at present too large for grinding down into flour. They are known
as semolina at this stage. They are taken to the next sieving machines -
|The purifier is an ingenious machine that not only separates the broken
parts of the wheat by sieving, that is, according to size, but it also separates
those parts which are of the same size but of different weight. This is
done by using currents of air. The skins are much lighter in weight than
the inner white floury parts, and a current of air is drawn upwards through
the mixture on the sieve, lifting up and 'floating' the skins, but allowing
the heavier white parts to remain on the sieve and be separated by the sieving
Sieving on the plansifters and purifiers will eventually have removed most of the brown skins. Now the inner floury portions of the broken wheat grains are brought together for final milling between the 'reduction' rolls. These are smooth rolls which mill down very gradually and accurately the inner white portions of the wheat (the endosperm or semolina) into a smooth, powdery, 'lively' flour.
Thus flour, clean bran and wheatfeed are collected, each in its own channel, from a large number of different machines and are finally brought either to bulk storage bins or to a packing floor where they are filled into sacks and weighed.
Mill Control Room
Lastly, the packed products are sent to the mill warehouse and stacked ready for dispatch. However, around 70% of the flour is dispatched in bulk. Some idea of the need for this section of the mill may be gathered when it is remembered that a large modern flour mill may produce around 750 tonnes per day.
The whole process of cleaning, and milling, etc., is done by machine, with the material passing automatically from machine to machine, and from one stage to the next. No hand touches the wheat from the moment it arrives, throughout its long journey in the mill, until the flour leaves the mill on lorries for the baker, biscuit-maker and other users.
Today the range of flours available is wider than ever before. Each type of flour has been milled with specific uses in mind.
Flours vary in their composition and, broadly speaking, are
defined by their rate of extraction.
This refers to the percentage of whole cleaned wheat grain that is present in the flour.
The three basic flour categories are:
|Wholemeal -||100 percent extraction, made from the whole wheatgrain with nothing added or taken away.|
|Brown -||usually contains about 85 per cent of the original grain, some bran and germ have been removed. This flour is frequently labelled as "85 per cent flour" rather than brown.|
|White -||usually 75 per cent of the wheatgrain. Most of the bran and wheatgerm have been removed during milling.|
Other varieties of flour:
|Wheatgerm -||white or brown flour with at least 10% added wheatgerm.|
|Malted wheatgrain -||brown or wholemeal flour with added malted grains.|
|Stoneground -||wholemeal flour ground in traditional way between two stones.|
|Organic -||flour milled from a wheat grown and processed naturally without the use of chemicals.|
|Some recipes for making bread can be found here.|