HOW GRAIN BECOMES FLOUR.
In order to make bread, the first operation is to grind the corn, be
it wheat, rye, barley, or oats, and we have already seen the rough
methods used by primitive man and others to effect this; we have noted
the mealing stones, the pestle and mortar, the hand quern, and the
grinding of corn by the Greeks and Romans. They soon gave up man as a
motive power, and substituted mules or horses; these in their time gave
place to water, which is a cheap and, if there be anything like a fall,
a very powerful motor—hence the mills dotted all over the country, by
the side of brook or river, with their water-wheels either over or
undershot Very picturesque are they mostly, and the drowsy murmur of
the wheel and the gentle splashing of the water are very pleasant We
are seeing the last of them; they have done their work and must be
thrown aside, for no one in his senses, who had water-power, would now
erect water-wheels when he could get a turbine.
As with the water-wheel, so its congener, the windmill, beloved of
artists, is going. A motive power as cheap as water is the wind, but,
unfortunately, it is not so reliable. It is believed that the Chinese
were the first to use the wind as a motive power for mills, and we
have no record as to when they were introduced into Europe; we only
know they were in use in the twelfth century. As a rule, in England,
windmills have four arms, or ‘whips,’ but sometimes they have six.
These arms are generally covered with strong canvas, but occasionally
they are covered with thin boarding; they are set at an angle, which
varies according to the fancy of the miller, but the shaft to which
they are attached (called the ‘wind shaft’) is invariably placed at
an inclination of 10 or 15 degrees, in order that the revolving arms
should clear the bottom portion of the mill.
[Illustration: A POST MILL.]
[Illustration: A WATER-WHEEL MILL.]
The oldest kind of windmill is called a _post_ mill, because the
whole structure is centred on a post, or pivot, and, when the wind
shifts, the mill has to be turned bodily to meet it, by means of a long
lever. The _smock_, or _frock_, windmill is an improvement upon the
post mill; the building itself is stationary and permanent, but the
head or cap, where is the wind shaft, rotates, and this is more easily
managed.
For hundreds of years people were contented with the four and six arms
to their windmills, and it was only in modern times that Messrs. J.
Warner and Sons, of Cripplegate, London, patented their annular sails,
which, as is plain to the meanest capacity, are vastly superior. The
shutters, or ‘vanes,’ are connected with spiral springs, which keep
them up to the best angle of ‘weather, for light winds. If the strength
of the wind increases, the vanes give to the wind, forcing back the
springs, and thus the area on which the wind acts diminishes. In
addition, there are a striking lever and tackle for setting the vanes
edgeways to the wind, when the mill is stopped, or a storm expected.
We have seen how from the very first man used stones wherewith to
triturate his corn, and to this day stones are still used for grinding,
although their days are in all probability numbered, and in a very
little time they, with the windmill, will be relegated to limbo. The
_Encyclopædia Britannica_ gives such an excellent description of these
mill-stones, that I quote it in its entirety.
[Illustration: THE GRINDING SURFACE OF A MILLSTONE.]
‘They consist of two flat cylindrical masses inclosed within a wooden
or sheet metal case, the lower, or _bed-stone_, being permanently
fixed, while the upper, or _runner_, is accurately pivoted and
balanced over it The average size of millstones is about four feet two
inches in diameter, by twelve inches in thickness, and they are made
of a hard but cellular siliceous stone, called buhr-stone, the best
qualities of which are obtained from La-Ferté-sous-Jouarre, department
of Seine et Marne, France. Millstones are generally built up of
segments, bound together round the circumference by an iron hoop, and
backed with plaster of Paris. The bed-stone is dressed to a perfectly
flat plane surface, and a series of grooves, or shallow depressions,
are cut in it, generally in the manner shown, which represents the
grinding surface of an upper or running stone. The grooves on both are
made to correspond exactly, so that when the one is rotated over the
other the sharp edges of the grooves, meeting each other, operate like
a rough pair of scissors, and thus the effect of the stones on grain
submitted to their action is at once that of cutting, squeezing, and
crushing. The dressing and grooving of millstones is generally done
by hand picking, but sometimes black amorphous diamonds (_carbonado_)
are used, and emery wheel dressers have likewise been suggested. The
upper stone, or runner, is set in motion by a spindle on which it is
mounted, which passes up through the centre of the bed-stone, and there
are screws and other appliances for adjusting and balancing the stone.
Further provision is made within the stone case for passing through air
to prevent too high a heat being developed in the grinding operation,
and sweepers for conveying the flour to the meal spout are also
provided.
‘The ground meal delivered by the spout is carried forward in a
conveyor, or creeper box, by means of an Archimedean screw, to the
elevators, by which it is lifted to an upper floor to the bolting or
flour-dressing machine. The form in which this apparatus was formerly
employed consisted of a cylinder mounted on an inclined plane, and
covered externally with wire cloth of different degrees of fineness,
the finest being at the upper part of the cylinder, where the meal
is admitted. Within the cylinder, which was stationary, a circular
brush revolved, by which the meal was pressed against the wire cloth,
and, at the same time, carried gradually towards the lower extremity,
sifting out, as it proceeded, the mill products into different grades
of fineness, and finally delivering the coarse bran at the extremity of
the cylinder. For the operation of bolting or dressing, hexagonal or
octagonal cylinders, about three feet in diameter, and from 20 to 25
feet long, are now commonly employed. These are mounted horizontally
on a spindle for revolving, and externally they are covered with silk
of different degrees of fineness, whence they are called “silks,” or
“silk dressers.” Radiating arms or other devices for carrying the
meal gradually forward as the apparatus revolved, are fixed within
the cylinders; and there is also an arrangement of beaters, which
gives the segments of cloth a sharp tap, and thereby facilitates the
sifting action of the apparatus. Like all other mill machines, the
modifications of the silk dresser are numerous,’
We have seen the ordinary operation of grinding flour in the
old-fashioned way; now let us notice the improvements in making wheat
into flour.
‘We will suppose that the wheat has arrived by lighter at one of the
large mills on the Thames, and that it has been shovelled into sacks
and hoisted into the warehouse. The process by which it is turned into
flour may be divided into three stages: (1) cleaning, (2) breaking, (3)
grinding; but the number and complexity of the operations included in
these stages are astounding. It must be understood that the following
description refers to a first-class London mill—that is, one which has,
certainly no superior, and, probably, no equal, in the world.
‘In the first stage the wheat is merely prepared for the mill,
and this is done in the cleaning department, which is separate
from the mill proper. From the warehouse the grain is passed to a
sifter or “separator,” which is a kind of sieve. Here the grosser
impurities—straw, sticks, stones, earth, seeds, and what not—are
removed. Thence to an “elevator,” precisely similar in principle to
that previously described, and by the elevator straight to the top of
the building. Here it enters a wire sieve in the form of a revolving
hexagonal “reel,” by which the smaller heavy impurities with which it
is still mixed are separated. Passing through this, it drops into the
next storey, to be subjected to the “aspirator,” an apparatus by means
of which currents of air are blown through the grain as it falls and
carry off the lighter and more volatile rubbish mixed with it. In the
next floor is an ingenious instrument with a special purpose. Among
the wheat is still a quantity of small black seeds, known as “cockle”
seeds, and to get rid of these the “cockle cylinder” is employed. It is
a revolving metal cylinder, the inner surface of which is fitted with
small holes; the grain passes into the interior of the cylinder, and
as the latter goes round and round the cockle seeds stick in the small
holes and are carried up to a certain height, when they fall out and
are caught by an “apron”; while the wheat, which is too large to stick
in the holes, continually falls back into the bottom of the cylinder.
Again our corn drops a storey, and encounters the “decorcitator.” The
object of this apparatus is to knock off the dust and dirt adhering
to the grains, and it is effected by agitating them between two metal
surfaces at a high rate of speed. The amount of dust removed by this
method from apparently clean grain is astonishing. In the next storey
is another decorcitator, and below that a second aspirator, which
brings us once more to the ground.
‘On reaching the ground floor again, our now clean wheat is first
passed through the “grading” or “sizing” reels, which separate it into
two sizes, and then it enters the mill proper. It should be said here
that the milling industry of the world has been revolutionised within
the past few years by the substitution of steel rollers for the old
millstones. The process of crushing or grinding, however, by steel
rollers is accomplished in a very gradual manner, as will be explained:
First come the “break rolls.” These are solid steel rollers set in
pairs, with corrugated surfaces; this gives them a cutting action.
Wheat is passed through five successive pairs of these rollers. The
first are about 1/16th inch apart, and only break or bruise the grain
slightly. Each successive pair is set closer, and carries the bruising
a step further. But this is only half the business. After each set of
rollers the grain goes through a “purifier,” which is either a sieve of
some kind or an aspirator, or both together, and the object is always
the same—namely, to separate the solid particles of the broken wheat
from the lighter ones. The former are, or rather will eventually be,
flour; the latter constitute “offal.” And the whole art of milling is
merely an extension of this process; first reduction, then separation,
repeated over and over again. As the grain passes through each
successive set of rollers it is broken up finer and ever finer, and the
separating action of the “purifier” accompanies it step by step. The
solid particles grow smaller and smaller, the “offal” correspondingly
finer and finer. This is the process in brief, but there are endless
complications and refinements on the way. For instance, the solid
particles are not only separated but are themselves divided into groups
according to size. Then the offal often undergoes a further purifying
process. Then the purifiers differ—some are complex, others simple;
some of wire, others of silk; some revolve, others oscillate; some are
“aspirated,” others not; and so forth. Meanwhile, at the end of the
five rolls and five purifiers, which make up our breaking department,
we have got three products: (_a_) semolina; (_b_) middlings; (_c_)
offal. The first two are practically varieties of the same—_i.e._,
both solid particles, which will afterwards be flour, but of different
sizes. They are half way between grain and flour—hence the term
“middlings.”
‘Grinding is only a continuation of the above process, but the rollers
are different; their surfaces are smooth, and they are set closer
together. The purifiers, too, are, for the most part, more elaborate.
A look at one of them will show the extreme ingenuity expended on
these operations. It consists primarily of an oscillating sieve made
of silk, through the meshes of which the particles of flour fall into
a wooden bin. On the floor of the bin is a “worm” which continually
works the flour along to one end; on the under surface of the sieve is
a travelling brush which brushes off the adhering flour and prevents
the meshes from getting clogged. Above the sieve is an apparatus which,
with the aid of currents blown by an aspirator, catches the volatile
offal; and above that again a travelling blanket which arrests the
still more volatile particles. Finally, the blanket, as it reaches the
end, is tapped automatically to knock out what has stuck to it. By the
time a handful of grain has been converted into a handful of fine flour
it has gone through some 50 different machines, including 18 sets of
rollers and 18 purifiers.
‘The following points may be of interest: A first-class London mill
working 100 sets of rollers can turn out 45 sacks of flour per hour.
Offal, according to its fineness or coarseness, forms bran, pollard,
etc., and is worth from 5_l._ to 6_l._ a ton. The qualities of flour
are whiteness and strength. The former is tested by the eye, the
latter only really by baking capacity. There seems to be a general
consensus of opinion in favour of flour made from Hungarian wheat. The
best English is of sweeter flavour, but lacks “strength.” It has been
reckoned that 300 sacks are made per hour in London mills, all of which
is consumed in London. The flour mill industry owes nothing to American
inventive genius; on the contrary, that country is behind the times.
The steel rollers came originally from Hungary—always a great milling
country.’