FLOUR MILLING.-THE ELECTRIC MIDDLINGS PURIFIER.
Scientific American April 9, 1881
However simple in outward appearance, a grain of wheat exhibits, when looked into,, a curious complexity of structure, organically as well as chemically; and the processes now employed in converting grain into flour are scarcely less complex and curious. Indeed, unless one has made a special study of modern milling he can have no idea of the many processes of reduction and purification a grain of wheat now undergoes between the bin and the flour barrel.
It is doubtful whether any other great industry has during the past ten years experienced so complete a revolution as flour making. For the previous half century or more, from the day when Oliver Evans set up the first automatic milling machinery in his mill on the Brandywine, the industry grew in volume and importance, but underwent no signal or radical improvement in machinery or processes. The non-progressive period came to an end about 1870; and since then change, and rapid radical change, has been the order of the day, at least in the great merchant mills, which turn out by far the larger and better portion of American flour.
The causes which led to the era of change were several, chief among them the conditions and exigencies of wheat growing in the new Northwest, the development of cheap railway communication with the seaboard, and the resulting possibility of competing with Austria and Hungary in supplying the flour markets of Western Europe. The problem was to make good white flour out of the spring wheat of Minnesota, and the processes of milling were revolutionized for its solution. To describe in detail even the more characteristic changes in the means and methods of milling thus brought about does not fall within the scope of this paper. It is necessary, however, to indicate roughly the more important of them to enable those of our readers who are not millers to appreciate the improvement in milling processes to be described and illustrated below.
Structurally the wheat kernel is composed of the following parts:
(1) The light, straw like, valueless hull, comprising the three parts called epidermis, epicarp, and endocarp, together making about 3 per cent of the weight of the grain.
(2.) The testa or episperm, which forms, with an underlying membrane, the inner skin of the berry. This part carries the coloring matter, and constitutes about 2 per cent of the weight.
(3.) The germ and its membranous expansion, say 5 per cent; nutritious but not desirable in the flour, since it carries an oil likely to become rancid and injure the sweet¬ness of the flour.
(4.) The central or floury portion, 90 per cent, composed of starch and gluten variously combined.
The heart is the softest, and contains the least gluten. In the successive layers around the center the proportion of gluten increases outward, the entire amount varying with the kind of grain, the quality of the crop, etc., etc.
The old process of milling involved but two distinct operations after the wheat had been cleaned—the grinding and the bolting, or separation of flour from bran. Three products were obtained: fine flour, more or less discolored by particles of 1 and 2; a coarser and more granular part, rich in gluten and dark in color, called middlings; and bran, more or less mixed with the other two.
To obtain the largest possible yield of flour the stones were set close together, or the upper stone "low." With soft, starchy, winter wheat, having a tough husk, low grinding gave excellent flour. With the hard and brittle hulled spring wheat the flour was mixed with so much fine bran, which could not be bolted out, that it was unpopular and' unprofitable.
The new process was designed to remove these objections to the flour made from Minnesota wheat. The aim now be-came, not to make the most fine flour and the least middlings at a grinding, but the reverse; it being found that, when properly purified or freed from branny particles, the middlings yielded a flour as white as that from winter wheat and much stronger, owing to its larger percentage of gluten. The new method was characterized as high grinding, the stones being set so far apart at first as to granulate rather than crush the kernel.
The stages of this process were four:
(1) the granulation of the berry;
(2) the separation of the product (" chop" or meal) by bolting into fine flour from the starchy center of the grain, the middlings or hard glutinous portions, and the coarser bran ;
(3) the purification of the middlings by an air blast, which winnowed away the bran mixed with them; (4) the regrinding and rebolting of the middlings, thus getting a strong, white, "fancy," or " patent " flour.
Under the stress of competition and the necessity of obtaining larger and larger yields of high quality flour, through the increase of middlings and the more perfect separation of discoloring elements, the still more complicated processes of gradual reduction were developed. By this method the aim is to remove the hull as completely as possible with the least breaking, to separate the weak flour of the heart of the grain from the rest, and to convert the more glutinous parts of the berry into high grades of flour by slow and-gradual reductions, each time subjecting the several grades of middlings to successive purifications and subsequent reductions by means of high grinding, or by crushing between rollers. It thus came to pass that the work of purifying middlings became the most important part of the milling operation, and the purifiers and their appurtenances the most conspicuous and characteristic portion of the machinery of the flour mill.
The higher quality of the flour produced justified the greater cost and trouble, but the system was not all gain. The fine flour-dust blown about the mill, particularly through the systems of purifiers and into the settling rooms or dust houses, was soon found to be as explosive as gun-powder; and several mills were wrecked by the careless handling of lights or by chance sparks from the rolls or stones firing the dust in the atmosphere of the mill or in the purifiers. The inapplicability of the purifying system to the smaller custom mills, which constitute numerically the larger part of the milling interest, was another though minor objection, the chief objections being the extra life and fire risk I involved; the cost and cumbersomeness of
the purifying systems; the power required to operate them; the space required for dust houses; the wastefulness of the system, some of the finer flour being blown away with the bran; and the largely increased complication of the work of flour making.
Impressed by the prevailing discontent of millers, both at home and abroad, with respect to the weans of purifying middlings in general use, a young American miller, Mr. Kingsland Smith, naturally gave much thought to the problems involved. While making a practical study of the European systems of milling in 1876 and 1877, Mr. Smith conceived the idea of using frictional electricity to remove the bran, and experimented enough with an electrically excited hard rubber roller to convince him-self that the matter was worthy of investigation. On his return home, he referred the problem to his friend and former classmate, Mr. Thomas B. Osborne, of New Haven, whose inventive talent he had a high respect for. Young Osborne, then a student at Yale College, undertook the task, and in a short time devised the plan of the desired machine. It consisted of a series of hard rubber rolls (electrified by the friction of hair, silk, wool, or other suitable material), under which rolls the middlings were to pass slowly along a shallow receiver, the latter being rapidly shaken so as to bring the bran to the top. The expectation was that the particles of light bran would be attracted to the revolving rolls, where they would cling until carried over a bran receiver into which they could be brushed.
His principal doubts were whether the electrified rolls would not also attract the floury particles, and whether the material attracted might not be repelled so quickly as to defeat the desired object. Both these doubts were dissipated by the action of the first working model of the machine. The principle of his device being happily established, Mr. Osborne added the necessary attachments, and had made a working machine with twelve rolls. This machine was tested in New Haven about a year ago, and from its successful working attracted much attention. It remained to be proved, however, whether the machine would be equally efficient in practical use in all sorts of weather. To settle this question a machine was placed in the Atlantic Mills, Brooklyn, N. Y., where, since May, 1880, it has been run almost continuously as a part of the mill machinery. The construction and appearance of the electric purifier will be made clear by the engraving on our front page. The material to be purified Middlings, bran, and flour dust in whatever combination—is received at the further end, and passes slowly under the rolls about two inches below. The agitation of the sieves causes the bran to rise to the surface, whence the light particles leap to the rolls and cling thereto until brushed into a shallow gutter placed in front of each roll. Meantime the heavy and electrically rejected middlings descend by gravity and pass through the bolts in the order of their fineness. Traveling brushes constantly sweep the bran from the gutters into the bran receiver on the left side of the purifier, in which is seen the spiral conveyor. By the time the last line of rolls is reached the material has been successively diminished by the abstraction of the bran and the screening out of the several grades of middlings, until only a trifling quantity of heavy refuse (if there be any) is left to pass over the tail of the purifier into the spout provided for it.
The power required to operate the purifier and generate the electricity employed is so slight that a man can work the entire machine with one hand. The trial machine in the Atlantic Mills purifies over fifty barrels of middlings a day, and its efficiency appears to be entirely unaffected by lapse of time or atmospheric changes. The machine occupies a space nine feet long, five and a half feet high, and three feet wide. The proprietors of the mill say that it works equally well on spring and winter wheat, and on all grades of middlings, and absolutely without dust. Dust-house material, when passed through the electric purifier, yields fully half its weight of fine flour and middlings suitable for flour. This alone would effect great economy in the working of large mills employing air purifiers. Compared with the best air purifiers in use, by weighing materials and products, the difference in favor of electric purifying is found to be from six to eight per cent. The saving of space and power is even more remarkable, the extra room required for air purifying and the power needed to drive the machinery and supply the blast being equivalent to one-tenth the capacity of a mill; in other words, without any addition to the power employed, the output of a mill may be increased ten per cent by the introduction of electric purifiers. For example, the Atlantic Mills have a maximum capacity of 700 barrels a day, and average 600 barrels. The space saved by displacing the air purifiers is 2,500 square feet. At the same time the engine is relieved of work requiring 22 horse power, now employed in driving the tans and other purifying apparatus. The power saved by electric purifying will easily grind 60 bar¬rels a day, and the space saved will amply accommodate the stones and other machinery required to increase the average output to 660 barrels a day.
In dispensing with the use of air blasts, there is no possibility of filling the air of the mill or any part of it with ex-plosive starch dust, and the serious problem of insurance is thus materially simplified. With the source of hazard removed the excessive rates charged for insuring flour mills would be unnecessary.
Taking into account, therefore, the great saving in cost of machinery, in power required, and in space; the more rapid action of the bolts since the material meets with no resistance in passing through the meshes; the more perfect separation of the bran from the flour products; the diminished waste; the fewer processes required to achieve a given result.; the diminished fire risk from the absence of dust; the great simplification of the work of milling promised by electric purification and the possible increase in the capacity of mills, the new system can scarcely fail to meet with immediate attention if not favor at the hands of progressive millers. To those operating custom mills, it seems to offer especial advantages, since it makes possible the conversion of grain in small distinct lots into new process flour, giving each customer his own.
The ultimate importance of the new system, if wider application sustains the promise of its performance hitherto, must be enormous. Our annual wheat crop is equivalent to something like 100,000,000
barrels of flour. The proprietors of the Atlantic Mills say that, "after making all allowances and reductions, we estimate the saving in material alone effected by the electric purifier to be at least 10 cents on a barrel of flour, wheat being at present $1.20 per bushel." By this estimate, the saving of material in milling a year's crop of wheat would be $10,000,000, and this is but one of several savings made possible by electric purifying over purification by air blasts and the machinery now in use.
Little needs to be said in explanation of the detail illustrations, which tell their own story. Fig. 2 shows very clearly the appearance of the bran as it leaps from the sieves and clings to the rolls. The adhering bran is brushed off when it reaches the sheepskin cushion, which lightly touches the top of the roll to electrify the hard rubber. The bran trough in front of the roll has been omitted, to show the behavior of the bran more clearly. Fig. 3 shows the tail of the purifier broken, to expose the shoot for the tailings and the spiral conveyor further in, by which the several grades of middlings are conveyed to their respective delivery spouts.
The Smith-Osborne patents for this process of purifying middlings are owned by The Electric Purifier Company, of New Haven, Mr. John Rice, General Manager. New York office, 17 Moore Street.