FLOUR and FLOUR MANUFACTURE . The
See also:term " flour " (Fr. fleur, flower, i.e. the best
See also:part) is usually applied to the triturated farinaceous constituents of the wheat
See also:berry (see WHEAT); it is, however, also used of other cereals and even of leguminoids when ground into a
See also:fine powder, and of many other substances in a pulverulent state, though in these cases it is usual to speak of
See also:rye flour, bean flour, &c . The flour obtained from oats is generally termed oatmeal . In
See also:Great Britain wheaten flour was commonly known in the 16th and 17th centuries as
See also:meal, and up to the beginning of the loth century, or perhaps later, the term mealing
See also:trade was not infrequently used of the milling trade . The ancestor of the millstone was apparently a rounded
See also:stone about the
See also:size of a man's fist, with which
See also:grain or nuts were pounded and crushed into a
See also:rude meal . These stones grinding . grinding. are generally of hard
See also:sandstone and were evidently used against another stone, which by dint of continual hammering was broken into hollows . Sometimes the' crusher was used on the
See also:surface of rocks . St Bridget's stone, on the
See also:shore of Lough Macnean, is supposed to have been a
See also:primitive Irish
See also:mill; there are many depressions in the
See also:fate of the table= like
See also:rock, and it is probable that
See also:round this stone several
See also:women (for in early
See also:civilization the preparation of flour was peculiarly the
See also:duty of the women) would stand and grind, or rather pound, meal . Many such stones, known as Bullan stones, still exist in
See also:Ireland . Similar remains are found in the Orkneys and Shetlands; and it is on record that some of these stones have been used for flour-making within historic times .
See also:Bennett in his
See also:History of Corn Milling remarks that the
See also:Indians to this
See also:maize and crush it into a
See also:paste between loose stones .
In the same way the
See also:Omahas pound this cereal in holes in the rocks, while the
See also:Oregon Indians parch and pound the capsules of the yellow
See also:lily, much after the fashion described by
See also:Herodotus in his account of the
See also:ancient Egyptians . In California the
See also:Indian squaws make a sort of paste by crushing acorns between a round stone or "
See also:muller," and a cuplike hollow in the surface of a rock . Crushing stones are of different shapes, ranging from the primitive '
See also:ball-like implement to an elongated shape resembling the pestle of a
See also:mortar . Mullers of the latter type are not infrequent among prehistoric remains in
See also:America,' while Dr
See also:Schliemann discovered several == specimens of the globular
See also:form on the reputed site of the city of ,Troy, and also among the ruins of '
See also:Mycenae . As la
See also:matter of fact stone mullers survived in highly civilized countries into
See also:Modern days, if indeed they are now altogether '
See also:extinct . The
See also:saddle-stone is the connecting
See also:link between the primitive pounder, or muller, and the
See also:quern, which was itself the
See also:direct ancestor of the millstones still used to some extent ad in the manufacture' of flour . = The saddle-stone, the stonase.• first true grinding implement, consisted of a stone with a more dr less
See also:face on which the grain was spread, and in and along this hollow surface it was rubbed and ground into coarse meal . "Saddle-stories have been discovered in the sand caves of Italy, among the lake dwellings of
See also:Switzerland, in the dolmens of France, in the
See also:pit dwellings of the
See also:British Isles, and among the remains of primitive folk all the
See also:world over . The Romans of the classical
See also:period seem to have distinguished the saddle-stone from the quern . We find allusions to the mola trusatilis, which may be translated the thrusting mill "; this would fairly describe a backwards and forwards motion . The mola versatilis evidently referred to the revolving millstone or quern . In primitive parts of the world the saddle-stone is not yet extinct, as for instance in Mexico .
It is known as the metata, and is used both for grinding maize and for making the maize cakes known as tortillas . The same implement is apparently still in use in some parts ofSouth America, notably in Chile . According to Richard Bennett, the quern,. the first
See also:complete milling mathine, originated in Italy and is in all probability not older than the and century B.C . This is, however, Quern. a controverted point . Querns are still used in most primitive countries, nor is it certain that they have altogether disappeared from remoter districts of Scotland and Ireland . Whatever was their origin, they revolutionized flour milling . The rotary motion of millstones became the essential principle of the trituration of grain, and exists to-day in the rolls of the
See also:roller mill . The early quern appears to have differed from its descendants in that it was soniewhat globular in. shape, the
See also:lower stone being made conical, possibly with the idea that the ground flour should be provided with a downward flow to enable it to fall from the stones . This type did not, however, persist . Gradually the convexity disappeared and the surface of the two stones became
See also:flat or very nearly so . In the upper stone was a
See also:species of
See also:funnel, through which the grain passed as through a hopper, making its way thence, as the stone revolved, into the space between the
See also:running and the '
See also:bed stone . The ground meal was discharged at the periphery .
The runner, or upper stone, was provided with a wooden handle by which the stone was revolved: The typical
See also:Roman mill of the Augustan age may' be seen at
See also:Pompeii . Here, in what is believed to have been a public pistrinum or mill, were found four pairs of mill-stones . The circular
See also:base of these mills is 5 ft. in diameter and i ft. high, and upon it was fastened the
See also:meta, a blunt
See also:cone abbut 2 ft. high, on which fitted the upper millstone or catillus, also conical . These mills were evidently rotated by slave labour, as there was no
See also:room for the=perambulation of a
See also:horse or donkey, while the side-lugs in which the handle-bars were inserted are plainly visible . Slave labour was generally used up to the introduction of
See also:Christianity, but was finally abolished by the emperor
See also:Constantine, though even after his edict mills continued to be driven by criminals . The Romans are credited by some authorities with having first applied power to the
See also:driving of millstones, which ; they connected with
See also:water-wheels by a
See also:horizontal spindle through the intervention of bevel gearing . But long use of pliWer . after millstones had been, harnessed to water power slave labour was largely employed as a
See also:motive force . The water-mill of the Romans was introduced at a relatively early period into Britain . Domesday
See also:Book shows that England was covered by mills of a. kind at the
See also:time of the Norman
See also:conquest, and mentions some Soo mills in the counties of Norfolk and
See also:Suffolk alone . No doubt the mike of Domesday Book consisted of one pair of stones connected by rude gearing with a water-
See also:wheel . Windmills are said to have been introduced by the Crusaders, who brought them from the East .
Steam power is believed to have been first used in a British flour mill towards the close of the 18th century, when
See also:Boulton &
See also:Watt installed a steam engine in the Albion Flour Mills in
See also:London, erected under the care of
See also:Rennie . Another great engineer,
See also:William Fairbairn, in the early days of the 19th century,
See also:left the impress of his
See also:genius on the mill and all its accessories . He was followed by other
See also:engineers, and in the days immediately preceding the roller period many improvements were introduced as regards the balancing and driving of millstones . The introduction of the blast and exhaust to keep the stones cool was a great step in advance, while the substitution of
See also:gauze for woollen or
See also:linen bolting
See also:cloth, about the
See also:middle of the 19th century, marked another era in British milling . Millstones, as used just before the introduction of roller milling, were from 4 to 42 ft. in diameter by some 12 in. in thickness, and were usually made of a siliceous stone, known as buhr-stone, much of which came from the
See also:quarry of La Ferte-sous-Jouarre, in France . - Nine-tenths, or perhaps ninety-nine hundredths, of all the flour consumed in Great Britain is made in roller mills, that is, Roller mills in which the wheat is broken and floured by n,imnB: means of rollers, some grooved in varying degrees of fineness, some smooth, their
See also:work being preceded and supplemented by a wide range of other machinery . All roller mills worthy of the name are completely automatic, that is to say, from the time the raw material enters the mill warehouse till it is sacked, either in the shape of finished flour or of offals, it is touched by no human
See also:hand . The history of roller milling extends back to the first
See also:half of the 19th century . Roller mills, that is to say,
See also:machines fitted with rolls set either horizontally, or. vertically, or obliquely, for the grinding of corn, are said to have been used as 'far back as the 17th century, but if this be so it is certain that they were only used in a tentative manner . Towards the middle of the 19th century the
See also:firm of E . R . & F .
See also:Turner, of
See also:Ipswich, began to build roller mills for breaking wheat as a preliminary to the conversion of the resultant middlings on millstones . The rolls were made of chilled iron and were provided with serrated edges, which must have exercised a tearing
See also:action on. the integuments of the berry . These mills were built to the design of a German engineer, of the name of G . A .
See also:Buchholz, and were exhibited at the London
See also:exhibition of 1862, but they never came into general use . It has also been stated that as early as 1823 a French engineer, named Collier, of
See also:Paris, patented a roller mill, while five years later a certain
See also:Malar took out another French patent, the
See also:specification of which speaks of grooves and
See also:differential speeds . But the direct ancestors of the roller mills of the
See also:present day were brought out some time in the third
See also:decade of the 19th century by a Swiss engineer named Sulzberger . His apparatus was rather cumbrous, and the chilled iron rolls with which it was fitted consumed a large amount of power relatively to the work effected . But the Pester Walz-Mtihle, founded in 1839 by Count
See also:Szechenyi, a Hungarian nobleman, which took its name from the roller mills with which it was equipped by Sulzberger, was for many years a great success; some of its roller mills are said to have been kept at work for upwards of
See also:forty years, and one at least is preserved in the museum at
See also:Budapest . It may be noted that Hungarian wheat is hard and flinty and well adapted for treatment by rolls . Moreover, gradual reduction, as now understood, was more or less practised in Hungarian Hungary, even before the introduction of roller practice, milling . Though millstones, and not rolls, were used, yet the, wheat was not floured at one operation, as in typical low or flat grinding, but was reduced to flour in several successive operations .
In the first break the stones would be placed just wide enough apart to " end " the wheat, and in each succeeding operation the stones were brought closer together . But Hungarian milling was not then automatic in the sense in which British millers understand the word . For a long time a great
See also:deal of hand labour was employed in the
See also:merchant mills of Budapest in carrying about products from one machine to another for further treatment . This practice may have been partly due to the cheap labour available, but it was also the deliberate policy of Hungarian millers to handle in this way the middlings and fine " dunst," because it was maintained that only thus could certain products be delivered to the machine by which they were to be treated in the perfection of
See also:condition . The results were
See also:good so far as the finished products were concerned, but in the
See also:light of modern automatic milling the
See also:system appears uneconomical . Not only did it postulate an inordinately large
See also:staff, but it further increased the labour
See also:bill by the demand it made on the number of sub-foremen who were occupied in classifying, largely by
See also:touch, the various products, and directing the labourers under them . Hungarian milling still differs widely from milling as practised in Great Britain in being a longer system . This is due to the more minute subdivision of products, a necessary consequence of the large number of grades of flour and offals made. in Hungary, where there are many intermediate varieties of middlings and " dunst " for which no corresponding terms are available in an
See also:miller's vocabulary . It will be convenient here to explain the meaning of three terms constantly used by millers, namely, semolina, middlings and
See also:duns' . These three products of roller mills are practically identical in composition, but represent mld sedUnmo/'na,g,, different stages in the
See also:process of reducing the endo- inst. sperm of the wheat to flour . A wheat berry is covered by several layers of skin, while under these layers is the floury kernel or endosperm . This the break or grooved rolls tend to
See also:tear and break up .
The largest of these more or less cubical particles are known as semolina, whilst the
See also:medium-sized are called middlings and the smallest sized termed dunst . The last is a German word, with several meanings, but is used in this particular sense by German and
See also:Austrian millers, from whom it was doubtless borrowed by the pioneers of roller milling in England . If we were to
See also:lay a sample of fairly granular flour beside a sample of small dunst the two would be easy to distinguish, but place a magnifying
See also:glass over the flour and it would look very like the dunst . If we were to repeat this experiment on dunst and fine middlings, the former would under the glass present a strong resemblance to the middlings . The same effect would be produced by the putting side by side of large middlings and small semolina . This is a broad description of semolina, middlings and dunst . Semolina and middlings are more
See also:apt to vary in appearance than dunst, because the latter is the product of the later stages of the milling process and represents small particles of the floury kernel tolerably
See also:free from such impurities . as
See also:bran or fluff . The flour producing middlings must not be confounded with the variety of wheat
See also:offal which is also known to many English millers as middlings . This consists of husk or bran, more or less comminuted, and with a certain proportion of floury particles adherent . It is only
See also:fit for feeding beasts . The spread of roller milling on the continent of
See also:Europe was undoubtedly accelerated by the invention of
See also:porcelain rolls, by
See also:Friedrich Wegmann, a Swiss miller, which were brought into general use in the seventh decade of the 19th century, and are still widely employed . They are admirably fitted for the reduction of semolina, middlings and dunst into flour; and for reducing pure middlings, that is, middlings containing no bran or wheat husk, there is perhaps nothing that quite equals them .
They were introduced into Great Britain in 1877, or thereabouts, and were used for several years, but ultimately they almost disappeared from British mills . This was partly due to the fact that as made at that date they were rather difficult to work, as it was not easy to keep the rolls perfectly parallel . Another
See also:drawback was their in-adaptability to over-heavy feeds, to which the British, and perhaps still more the
See also:American, miller is frequently obliged to resort . However, since the beginning of the loth century some of the most advanced flour mills in England have again Porcelain rolls . taken to using porcelain rolls for some part of their reduction process . The
See also:birth of roller milling in Great Britain may be said to date from 1872, when Oscar Oexle, a German milling engineer, Roller erected a set of roller mills in the Tradeston Mills, m1/!mg in
See also:Glasgow . This was long before the introduction of In automatic roller mills . But the
See also:foundations of the England millstone system were not seriously disturbed till 1877, when a party of leading British and Irish millers visited Vienna and Budapest with the
See also:object of studying roller milling in its native home . In x878 J . H .
See also:Carter installed in the mill of J . Boland, of
See also:Dublin, what was probably the first complete automatic roller plant erected in the
See also:Kingdom, and in 188r a milling exhibition held at the Royal Agricultural
See also:Hall, London, showed the automatic roller system in complete operation .
From that time the roller system made great progress . By 1885 many of the leading British millers had installed full roller
See also:plants, and in the succeeding ten years small roller plants were installed in many
See also:country mills . For a time there was a transition stage in which there was in operation a number of so-called " combined " plants, that is to say, mills in which the wheat was broken on millstones or disk mills, while the middlings were reduced by smooth rolls; but these gradually dropped out of being . Well-found British flour mills at the present time are probably the best fitted in the world, and as a whole have nothing to fear from comparison with their American competitors . It is true that American millers were rather quicker to copy Hungarian milling methods so far as gradual reduction was concerned . But from about 188o the British miller was quite awake to his position and was straining every nerve to provide himself with a plant capable of dealing with every kind of wheat . It has often been said that he commands the wheat of the whole world . This is true in a sense, but it is not true that he can always command the exact kind of wheat he requires at the price required to meet
See also:foreign competition: Therein he is at a disadvantage . But engineers have done their best to meet this weak point, and by their assistance he is able to compete under almost all conditions with the millers of the whole world . Processes of Milling.—Fully to appreciate the various processes of modern milling, it must be remembered not only that the wheat as delivered at the mill is dusty and mixed with sand and even more objectionable refuse, but also that it contains many light grains and seeds of other plants . It is not therefore sufficient for the miller to be able to reduce the grain to flour on the most approved principles; he must also have at command the means of freeing it from foreign substances, and further of " conditioning " it, should it be
See also:damp or over dry and harsh . Again, his operations must be conducted with reference to the structure of the wheat grain .
The wheat berry is afruit, not a seed, the actual seed being the germ or embryo, a
See also:body which is found at the base of the berry and is connected with the plumule or
See also:root . The germ is tough in texture and is in roller milling easily separated from the
See also:rest of the berry, being flattened instead of crushed by the rolls and thus readily sifted from the stock . The germ contains a good deal of fatty matter, which, if allowed to remain, would not increase the keeping qualities of the flour . Botanists distinguish five skins on the berry—epidermis, epicarp, endicarp, episperm' and embryous membrane—but for
See also:practical purposes the number of integuments may be taken as three . The inner skin is often as thick as the
See also:outer and second skins together, which are largely composed of woody fibre; it contains the cerealin or aleurone cells, but although these are made up of a certain proportion of proteids, on account of the discolouring and diastasic action of the cerealin in flour they are best eliminated . The endosperm, or floury kernel, coming next to the inner skin, consists of
See also:starch granules which are caught as it were in the minute meshes of a
See also:net . This network is the
See also:gluten, and it may be noted that these meshes are not of equal consistency throughout the berry, but are usually finer and more dense near the husk than in the interior of the kernel . This glutinous portion is of great importanceto the
See also:baker because on its quantity and quality depends the " strength or rising power of the flour, and the aim of modern roller milling is to retain. it as completely as possible, a matter of some difficulty owing to its close adherence to the husk, especially in the richest wheats . Another
See also:organ of the wheat berry which has a most important bearing on the work of the miller is the
See also:placenta, which is in effect a
See also:cord connecting the berry with its stalk or
See also:straw . The placenta serves to
See also:filter the
See also:food which the plant sucks up from the ground; it passes up the crease of the berry, and is enfolded in the middle skin, being protected on the outer side by the first and having the third or inner skin on its other side . A good deal of the matters filtered by the placenta are
See also:mineral in their nature, and such portions as are not digested remain in the crease . This is the matter which millers
See also:call " crease dirt." It is highly discolouring to flour, and must be carefully eliminated .
The fuzzy end of the berry known as the
See also:beard also has a distinct
See also:function; its hairs are in reality tubes which serve to carry off superfluous moisture . They have, in
See also:common with the bran, no nutritive value . (See also WHEAT.) In the old " flat " or " low " milling the object was to grind as perfectly as possible, at one operation, the central substance of the grain, constituting the flour, and to
See also:separate it from the embryo and outer skins constituting the bran . In " high " milling, on the other hand, the grinding is effected in a series of operations, the aim being to get as much semolina and middlings as possible from the wheat, and to make as. little flour as possible during the earlier or " breaking " part of the process . It is impossible altogether to avoid the production of flour at this stage, but properly set and worked break-rolls will make as little as 15% of " break-flour," which is of less value, being contaminated with crease dirt, and also because it is weak owing to the
See also:absence of the gluten cells which adhere more readily to the middlings . Whole wheaten flour, some-times called
See also:Graham flour, consists of the entire grain ground up to a
See also:uniform mass . Wheat cleaning has been well called the foundation of all good milling . In the
See also:house, as the wheat-cleaning department of the mill is termed, will be found an array of machinery
See also:Bry almost equal in range and variety to that in the mill ning itself . The wheat,
See also:drawn by an elevator from the
See also:barge, cle a or hoisted in sacks, is first treated by a machine known as a
See also:ware-house separator . This apparatus accomplishes its work by means of flat
See also:sieves, some of which will be of much coarser mesh than others, and of air currents, the
See also:adjustment of which is a more delicate task than might appear . The warehouse separator serves to free dirty wheat of such impurities as lumps of
See also:earth, stones, straws and sand, not to mention small seeds, also some maize, oats and
See also:barley . Great care has to be exercised in all operations of the screen house lest wheat should pass away with the screenings .
Besides the warehouse separator, which is made in different types and sizes, grading and sorting cylinders, and what are known ascockle and barley cylinders, are much used in the screen house . These cylinders are provided with indents so shaped and of such size as to catch seeds which are smaller than wheat, and reject grains, as of barley or oats, which are longer than wheat . Sorting cylinders should be followed by machines known as scourers, the function of which is to free the wheat from adherent impurities . These machines are of different types, but all depend on percussive action . A vertical scourer consists of a number of
See also:steel or iron beaters attached to a vertical spindle which revolves inside a metallic
See also:woven or perforated casing, the whole being fitted with an effectual exhaust . Scourers with horizontal spindles are also in great favour . Not every wheat is suitable for scouring, but some wheats are so mingled with impuritiesthat a severe action between the beaters and the perforated case is absolutely necessary . The most efficient scourer is that which frees the wheat from the greatest amount of impurity with a mini-mum of abrasion . The beaters should be adjustable to suit different kinds of wheat . Scourers are followed by
See also:brush machines which are similar to the last and are of three distinct types: solid, divided and cone brushes . In the solid variety the brush surface is continuous around the circumference of a revolving cylinder; in divided brushes there is often a set of beaters or bars covered with brush but leaving intermediate spaces; while the cone brush consists of beaters covered with fibre arranged like cones around a vertical spindle . The object of all these brushes, the cylinder containing them being fitted with an exhaust
See also:fan, is to
See also:polish the. wheat and remove adhering impurities which the percussive action of the scourer may have failed to eliminate, also to remove the beard or fuzzy end and any loose portions of the outer husk .
But the miller must be careful not to overdo the scouring action and unnecessarily abrade the berry, else he will have trouble with his flour, the triturated bran breaking under the rolls and producing powder which will discolour the break flour . To remove such metallic fragments as nails, pieces of
See also:wire, &c., magnets are used . These may either be of horseshoe shape, in which case they are usually set at the
See also:head of the wheat spouts, or they may consist of magnetized plates set at angles over which the wheat will slide . It is not a
See also:bad plan to place the magnets just before the first set of break-rolls; where they should ensure the arrest of steel and iron particles, which might otherwise get between the rolls and spoil the edges of their grooves, and also do damage to the sifting machines . Mention must also be made of the automatic scales which are used to check the milling value of the wheat . In principle these machines are all the same, though details of construction may vary . Each weigher is set for a given
See also:weight of grain . As soon as the receiving hopper has poured through a
See also:valve into the recipient or skip, which is hung at one end of a
See also:beam scale, a load of grain sufficient to overcome the weight hung at the other end of the beam, the inlet of grain is automatically cut off and the skip is discharged, automatically returning to take another
See also:charge . Each weighing is automatically recorded on a
See also:dial . In this way a record can be kept of the
See also:gross weight of the uncleaned wheat entering the warehouse and of the net weight of the cleaned wheat . The difference between the two weighings will, of course, represent the loss by cleaning . The percentage of flour obtained from a given wheat can be ascertained in the mill itself .
In practice the second weigher is placed just before the first break . The cleansing of wheat by washing only became a fine
See also:art at the close of the 19th century, though it was practised in the
See also:north of England some twenty years earlier . Briefly it may be said Wet that certain wheats are washed to free them from extranecteantng ous matters such as adherent earth and similar impurities and
See also:con- which could not be removed by dry cleaning without dttloning, undue abrasion . Such wheats are Indians, Persians and hard Russians, and these require not only washing but also conditioning, by which is meant mellowing, before going to the rolls . With another class of wheats, such as the softer Russians and Indians,
See also:spring Americans and Canadians, hard American winters, Californians and the harder
See also:River Plates, washing and conditioning by
See also:heat is also desirable, though care must be exercised not to let the moisture penetrate into the endosperm or floury portion of the kernel . In a third and distinct class fall soft wheats, such as many kinds of Plates, soft Russians and English wheat . It is generally admitted that while wheat of the first two divisions will benefit from the application of both moisture and heat, wheat of the third class must be washed with great circumspection . The object of washing machines is to agitate the wheat in water till the adherent foreign matters are washed off and any dirt balls broken up and drained off in the waste water . To this end some washers are fitted with Archimedean
See also:conveyors set either at an inclined
See also:angle or
See also:tally or vertically; or the washer may consist of a
See also:barrel revolving in a tank partly filled with water . Another function of washing machines is to separate stones of the same size which are found in several varieties of wheat . This separation is effected by utilizing a current of water as a
See also:balance strong enough to carry wheat but not strong enough to carry stones or bodies of greater specific gravity than wheat . This current may be led up an inclined worm or may flow horizontally over a revolving
See also:tray .
The washer is followed by a whizzer, which is an apparatus intended to free the berry by purely
See also:mechanical means from superfluous moisture . The typical whizzer is a vertical
See also:column fed at the bottom and delivering at the top . The wet wheat ascends by centrifugal force in a
See also:spiral direction round the column to the top, and by the time it is discharged from the spout at the top it has thrown off from its outer skin almost all its moisture, the water escaping through the perforated cover of the machine . But there still remains a certain amount of water which has penetrated the integuments more or less deeply, and to condition the berry it is treated by a combination of hot and
See also:cold air . The wheat is passed between perforated
See also:metal plates and subjected to a
See also:draught first of hot and then of cold air . The perforated plates are usually built in the shape of a column, or
See also:leg as it is often called, and this is provided with two air
See also:chambers, an upper one serving as a
See also:reservoir for hot, and the lower for cold air . The air from both chambers is discharged by pressure through the descending layers of wheat, which should not be more than an inch thick; the air is drawn in by a steel-
See also:plate fan, which is often provided with a divided casing, one side being used for cold, and the other for hot air . Coupled with the hot air side is a heater consisting of a series of circulating steam-heated pipes . The temperature of the heated air can be regulated by the supply of steam to the heater . This process of washing and conditioning, one of the most important in a flour mill, is characteristically British; millers have to deal with wheats of the most varied nature, and one object of conditioning is to bring hard and harsh, soft and weak wheats as nearly as possible to a common standard of condition before being milled . Wheat is some-times washed to toughen the bran, an end which can also be attained by damping it from a spraying
See also:pipe as it passes along an inclined worm . Another way of toughening bran is to pass wheat through a heated cylinder, while again another process known as steaming consists of injecting steam into wheat as it passes through a metal hopper .
Here the object is to cleanse to some extent, and to warm and soften (by the condensation of moisture on the grain), but these processes are imperfect substitutes for a full washing and conditioning plant . Hard wheats will not be injured by a fairly long
See also:im-mersion in water, always provided the subsequent whizzing and drying are efficiently carried out . The second class of semi-hard wheats already mentioned must be run more quickly through the washer and freed from the water as rapidly as possible . Still more is this necessary with really soft wheats, such as soft River Plates and the softer English varieties . Here an
See also:immersion of only a few seconds is desirable, while the moisture left by the water must be immediately and energetically thrown off by the whizzer before the grain enters the drier . Treated thus, soft wheats may be improved by washing . It is claimed that hard wheats, like some varieties of Indians, are positively improved in flavour by conditioning, and this is probably true; certain it is that English country millers, in seasons when native wheat was scarce and dear, and Indian wheat was abundant and cheap, have found the latter, mellowed by conditioning, to be an excellent substitute . Wheats which have been exposed to the action of water during
See also:harvest do not necessarily yield unsound flour; the matter is a question of the amount of moisture absorbed . But it must be remembered that it is not so much the water Effect of itself which degrades the constituents of the wheat damp . (starch and gluten) as the chemical changes which the dampness produces . Hence perhaps the best remedy which can be found for damp wheat is to dry it as soon as it has been harvested, either by kiln or steam drier at a heat not exceeding 120° F., until the moisture has been reduced to 10 % of the whole grain . The
See also:Hour made from wheat so treated may be weak, but will not usually be unsound .
The practice of drying damp flour has also good results . Long before the roller milling period it was found that only flour which had been dried (in a kiln) could safely be taken on long
See also:sea voyages, especially when the vessel had to navigate warm latitudes . It may be noted that in the days of millstone milling it was far more difficult to produce good keeping flour . The wheat berry being broken up and triturated in one operation, the flour necessarily contained a large proportion of branny particles in which cerealin, an active diastasic constituent, was present in very sensible proportions . Again, the elimination of the germ by the roller process is favourable to the production of a sounder flour, because the germ contains a large amount of oleaginous matter and has a strong diastasic action on imperfectly matured starches . The tendency of flours containing germ to become rancid is well marked . During the South
See also:African War of 1899—19o2 the British army supply department had a practical
See also:proof of the diastasic action of branny particles in flour . Soldiers'
See also:bread is not usually of
See also:colour, and the military authorities not unnaturally believed that comparatively low-grade flour, if sound, was eminently suitable for use in the
See also:field bakeries . But in the
See also:climate of South Africa flour of this description soon
See also:developed considerable acidity . Ultimately the supply department gave up buying any but the driest patent flours, and it is understood that the most suitable flour proved to be certain
See also:patents milled in Minneapolis, U.S.A., from hard spring wheat . Not only did they contain a minimum of branny and fibrous matters, but they were also the driest that could be found . After being cleaned the wheat berry is split and broken up into increasingly fine pieces by fluted rolls or " breaks." In the earlier years of roller milling it was usual to employ more breaks than is now the case .
The first pair of break-rolls used Break- to be called the splitting rolls, because their function was rolls. supposed to be to split the berry longitudinally down its crease, so as to give the miller an opportunity of removing the dirt between the two lobes of the berry by means of a brush machine . The dirt was in many cases no more than the placenta already described, which shrivelling up took, like all
See also:vegetable fibre, a dark tint . The neat split along the crease was not, however, achieved in more than 10 % of the berries so treated . Where such rolls are still in use they are really serving as a sort of adjunct to the wheat-cleaning system . Four or five breaks are now thought sufficient, but three breaks are not recommended, except in very
See also:short systems for small country mills . Rolls are now used up to 6o in. in length, though in one of the most approved systems they never exceed 40 in.; they are made of chilled iron, and for the breaking of wheat are provided with grooving cut at a slight twist, the spiral averaging 4 in. to the
See also:foot length, though for the last set of break-rolls, which clean up the bran, the spiral is sometimes increased to 1 in. per foot . The grooves should have
See also:sharp edges because they do better work than when blunt, giving larger semolina and middlings, with bran adherent in big flakes; small middlings, that is, little pieces of the endosperm torn away by blunt grooves, and comminuted bran, make the production of good class flour almost impossible; cut bran, moreover, brings less
See also:money . The break-rolls should never work by pressure, but nip the material fed between them at a given point; to cut or shear, not to flatten and crush, is their function . Rolls may be set either horizontally or vertically; an oblique setting has also come into favour . The feed is of the utmost importance to the correct working of a roller mill . The material should be fed in an even stream, not too thick, and leaving no part of the
See also:roll uncovered . The two rolls of each pair are run at unequal speeds, 22 to I being the usual ratio on the three first breaks, while the last break is often speeded at 3 to I or 31 to I ; in one of the oblique mills the difference is obtained by making the diameter of one roll 13 and of the other io in. and running them at equal
See also:speed .
For break-rolls up to 36 in. in length 9 in. is the usual diameter; for longer rolls to in. is the standard . To do good work rolls must run in perfect
See also:parallelism; otherwise some parts of the material will pass untouched, while others will be treated too severely . The products of the break-rolls are treated by what are known as scalpers, which are simply machines for sorting out these products Scalpers for further treatment . Scalpers may either be revolving reels or flat sieves . The
See also:sieve is the favourite form of scalper on account of its gentle action .
See also:Scalping requires a separating and sifting, not a scouring action . The break products are usually separated on a sieve covered with wire or perforated
See also:zinc plates . Generally speaking, two sieves are in one
See also:frame and are run at a slight incline . The throughs of the top sieve fall on the sieve below, while the rejections or overtails of the first sieve are fed to the next break . The " throughs," or what has passed this sieve, are graded by the next sieve, the tailings going to a purifier, while the throughs may be freed from what flour adheres to them by a centrifugal dressing machine and then treated by another purifier . A form of scalper which has come into general use on the continent of Europe, and to a lesser extent in Great Britain and America, is known as the plansifter . This machine, of Hungarian origin, is simply a collection of superimposed flat sieves in one box, and will
See also:scalp or sort out any kind of break stock very efficiently .
A system of grading the tailings, that is, the rejections of the scalpers, introduced by
See also:Harrison Carter (Carter-Ziemer patent), was known as pneumatic sorting . Its object was to supplement the work of the scalpers by classifying the tailings by means of air-currents . To this end each scalper was followed by a machine arranged some-what like a gravity purifier; that is to say, a current of air drawn through the casing of the sorter allowed the heaviest and best material to drop down straight, while the lighter stuff was deposited in one or other of further compartments formed by obliquely placed adjustable cant boards . So searching was this grading, that from the first sorter of a four-break plant four separations would be obtained, the first going to the second break, the second joining the first separation from the second sorter and being fed to the third break, while the third went with the best separation of the third sorter to the
See also:fourth break, and the last separation from all the sorters went straight into the bran
See also:sack . The work of the break-rolls was greatly simplified and reduced by this sorting process, as each particle of broken wheat went exactly to that pair of break-rollers for which it was suitable, instead of all the material being run indiscriminately through all the break-rollers and thereby being cut up with the necessary result of increasing the production of small bran . The object of the purifier, a machine on which milling engineers have lavished much thought and labour, is to get away from the Purifiers. semolina and middlings as much impure matteras possible, that those products may be pure, as millers say, for reduction to flour by the smooth rolls . The purifiers used in British mills take
See also:advantage of the fact that the more valuable portions of the wheat berry are heavier than the less valuable particles, such as bran and fibrous bodies, and a current of air is employed to weigh these fragments of the wheat berry as in a balance and to separate them while they pass over a silk-covered sieve . To this end the semolina or middlings are fed on a sieve vibrated by an eccentric and set at a slight downward angle . This sieve is installed in an air-tight
See also:longitudinal wooden chamber with glass windows on either side, through which the process of purifying can be watched . Up-wards through this sieve a fan constantly draws a current of air, which, raising the stock upwards, allows the heavier and better material to remain below while the lighter particles are lifted off and fall on side platforms or channels, whence they are carried forward and delivered separately . The good material drops through the meshes of the silk, and is collected by a worm . It is usual to clothe the sieve in sections with several different meshes of silk so that stock of almost identical value, but differing size, may be treated with uniform accuracy .
In good purifiers the strength of the current can be regulated at will in eachsection . The tailings of a purifier do not usually exceed to to 15 % of the feed . The clothing of purifier sheets must be nicely graduated to the clothing of the preceding machines . Repurification and even
See also:purification may be necessary under certain conditions . In Hungary and other parts of Europe, gravity purifiers are much in use . Here the material is guided along an open sieve set at a slight angle, while an air-current is drawn up at an acute angle . Under the sieve may be arranged a series of inclined boards, the position of which can be varied as required . The heaviest and most valuable products resist the current and drop straight down, while lighter material is carried off to further divisions . From the purifier all the stock except the tailings, which may require other treatment, should go to the smooth rollers to be made Smooth into flour, but here the rollerman will have to exercise roils . great care and discretion . Many of the remarks already made in regard to break-rolls apply to smooth rolls, notably in respect of parallelism . But instead of a cutting action, the smooth rolls
See also:press the material fed to them into flour .
This pressure, however, must be applied with great discrimination, large semolina with impurities attached requiring quite different treat- ment from that called for by small pure middlings . The pressure on the stock must be just sufficient and no more . Reduction rolls are usually run at a differential speed of about 2 to 3 . The feed must be carefully graded, because to pass stock of varying size through a pair of smooth rolls would be fatal to good work . Scratch rolls very finely grooved are used for cracking impure semolina or for reducing the tailings of purifiers . The latter often hold fragments of bran, which are best detached by rolls grooved about 36 to the inch and run at a differential of 3 to i . The reduction requires even more roll surface than the break system . To do first-class work a mill should have at least 35 to 40 in. on the breaks and 50 in. on the reduction for each sack of 280 lb of flour per hour . Many engineers consider too to 110 in. on the break, scratch and smooth rolls not too much . The dressing out of the flour from the stock reduced on smooth rolls is generally effected by centrifugal machines, which consist of a slowly revolving cylinder provided with an
See also:internal pressing.
See also:shaft on which are keyed a number of iron beaters that run at a speed of about 200 revolutions a minute, and fling the feed against the silk clothing of the cylinder . What goes through the silk is collected by a worm conveyor at the bottom of the machine . Most centrifugals have so-called " cut-off " sheets, with internal divisions in the tail end ; these are intended to separate some intermediate products, which, having been freed from floury particles, are treated on some other machine, such as a pair of rolls either direct or after a purifier .
The centrifugal is undoubtedly an efficient flour separator, but the plansifters already mentioned are also good flour-dressers, especially in dry climates . A plansifter mill will have no centrifugals, except one or two at the tail end where the material gets more sticky and requires more severe treatment . The yield of flour obtained in a British roller mill averages 70 to 73% of the wheat berry . The
See also:residue, with the exception of a very small proportion of waste, is offal, which is divided into various grades and sold . Profitable markets for British-made bran have been found in Scandinavia, and especially in Denmark . In mill-stone milling the yield of flour probably averaged 75 to 8o %, but a certain proportion of this was little more than offal . The length of the flour yield taken by British millers varies in different parts of the kingdom, because demand varies . In one locality high-class patents may be at a premium; in another the call is for a straight grade, i.e. a flour containing as much of the farinaceous substance as can be won from the wheat berry . In one
See also:district there is a sale for
See also:rich offals, that is, offals with plenty of flour adhering; in another there may be no demand for such offals . Hence, though the general principles of roller milling as given above hold good all over the country, yet in practice the work of each mill is varied more or less to suit the peculiarities of the
See also:local trade . Early in the 19th century a French chemist, J . J .
E . Poutet, discovered that nitrousacid and oxides of nitrogen
See also:act on some fluid and semi-fluid vegetable oils, removing their yellow
See also:Bleaching tinge and converting a considerable portion of their sub- of flow . stance into a white solid . The importance of this dis- covery, when the
See also:physical constitution of wheat is considered, is obvious, but it was years before any attempt was made to bleach flour . The first attempts at bleaching seem to have been made on the wheat itself rather than on the flour . In 1879 a process was patented for bleaching grain by means of chlorine
See also:gas, and about 1891 a
See also:suggestion was made for bleaching grain by means of electrolysed sea-water . In 1895 a
See also:scheme was put forward for treating grain with sulphurous acid, and about two years later it was
See also:pro-posed to subject both grain and flour to the influence of electric currents . In 1893 a patent was granted for the purification of flour by means of fresh air or
See also:oxygen, and three years later another inventor proposed to employ the Rontgen rays for the same purpose . In 1898 Emile Frichot took out a patent for using
See also:ozone and ozonized air for flour-bleaching . The patent (No . 1661 of 1901) taken out by J . & S .
See also:Belfast recited that flour is known to improve greatly if kept for some time after grinding, and the purpose of the invention it covered was to bring about this improvement or conditioning not only immediately after grinding, but also to a greater extent than can be effected by keeping . The process consisted in subjecting the flour to the action of a suitable gaseous oxidizing medium; the inventors preferred air carrying a minute quantity of nitric acid or peroxide of nitrogen, but they did not confine them-selves to those compounds, having found that chlorine, bromine and other substances capable of liberating oxygen were also more or less efficacious . They claimed that while exercising no deleterious action their treatment made the flour whiter, improved its
See also:baking qualities, and rendered it less liable to be attacked by mites or other organisms . Under the. patent, No . 14006 of 1903, granted to J . N .
See also:Alsop of
See also:Kentucky the flour was treated with atmospheric air which had been subjected to the action of an arc or flaming
See also:discharge of
See also:electricity, with the purpose of purifying it and improving its nutritious properties . The Andrews and Alsop patents became the
See also:objects of extended litigation in the English courts, and it was held that the gaseous medium employed by Alsop was substantially the same as that employed by Andrews, though produced electrically instead of chemically, and therefore that the Alsop process was an infringement of the Andrews patent . Various other patents for more or less similar processes have also been taken out . (G . F .
GUSTAVE FLOURENS (1838-1871)
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