Malt Mills and Malt Milling


Mr. Albert E. Taylor in the Chair.

The following paper was read and discussed:—

Malt Mills and Malt Milling
by Thomas R. Callon.

The subject of malt mills and their working, which I propose to deal with, is one on which there has been little or no information published. As a practical engineer, and having had experience with various types of mills, I consider that such a subject could not be devoid of interest to those who are continuously engaged in the use of ground malt, prepared by passing through one or other of the various mills which I intend to describe. I propose first to give a description of the gradual improvements and inventions. The use of mill stones dates back at least 6000 years, and for 4000 years nothing but hand stones, or stone pestle and mortar were employed, worked chiefly by women.

The hand stone or quern, in use 4000 B.C. consisted of a stone slab, slightly hollow in the centre to hold the grain, whilst large stones were pushed backward and forward, thus grinding the grain to the fineness required.

The slave or Kaffir-driven stones, 2000 B.C., driven by the slaves, consisted of two stones of equal diameter, the bottom stone being fixed while the top stone, which runs loose, is shown to have a rough wood handle for two slave women to revolve it with.

A type was introduced 450 B.C., consisting of a pair of stones driven by a water wheel, and gave such excellent results as regards even grinding and output that the Romans took up the matter, and in the year 350 B.C. the water wheel with three or four pairs of stones driven off one shaft was introduced. The great objection to the water wheel was the uncertainty of the supply of water for driving.

The windmill was introduced A.D. 600, and found very great favour as a cheap means of grinding, and although universally adopted it entailed great expenditure in the carriage of grain, owing to the lofty positions which were always chosen so as to catch all the available wind. This mill had an objection similar to the water wheel, namely, the uncertainty of the source of power.

In the year A.D. 1784 the windmill was superseded by the steam-driven mill, of which thousands are running at the present day, and have found such favour that it is with the greatest difficulty one can get people to appreciate the advantages of the roller system over and above that of stone grinding. In the year 1820 the first roller mill was introduced, but only in a very experimental form, and presented many difficulties in the way of obtaining uniform grinding. Granite rolls were first tried and found unsuitable, owing to flats wearing very quickly on the periphery of the roll, which allowed corns to pass through unbroken, therefore entailing enormous expense in constantly truing up the rolls. Granite rolls are never homogeneous in structure; like all other stones they possess soft veins which are detrimental for the purpose of grinding. Cast-iron rolls were next tried with rough cast surfaces, and these, though not wearing so quickly as the granite rolls, were found to be very difficult to fix on a shaft to give even running on the periphery, owing to the unequal shrinkage in the casting, so that they quickly shared the same fate as the granite rolls. The idea of the rough cast surfaces on the rolls was to give better biting action on the grain. Cast-iron rolls with chilled surfaces were the next to be tried, the rolls being keyed on to their respective shafts and then trued up in the lathe. This was found to be very efficient, and at a later stage grooves were cut on the surface, which materially increased the output of the mill. In mills with smooth rolls only, a difficulty is experienced with foreign seeds such as peas, which get mixed with the malt, and when entering the nip the rolls will not bite them, thus causing a block. The rolls then have to be thrown out to allow them to pass, and at the same time whole malt is allowed to pass also.

At first the grooves were cut in line with the axis of the roll, but the present day practice is at an angle of about 15° to that of the axis. Although there is no great advantage by adopting the latter, especially where there are, say, from 10 grooves to the inch and upwards, it is useful whore there are a small number of grooves, since it ensures one groove always being in contact with the grain being cracked. When the rolls were perfected the difficulty of an evenly distributed feed presented itself, and this was quickly overcome by the introduction of the coarse fluted feed roll, by which the feed could he spread over the rolls in an even and continuous stream.

It was not until the great flour milling exhibition, which was held in the Agricultural Hall, London, in the year 1881, that the development of the roller mill was accepted as being the right principle for the thorough separation of the husks and semolina, without injury to the husks. In the early days of roller milling the usual length of the roll was 12 to 14 inches; this was increased to 20 and 24 inches, and subsequently to 32 and 40 inches, and remained at this length for some time, but as the demand for output called for larger rolls, the mills were constructed with rolls 50 and 60 inches long, which latter dimension now stands as the maximum. Such mills are found to work very economically.

Roller milling in the brewing industry does not date very far back, the bulk of the grinding being done with French Burr stones, flat running, and three or four pairs of stones being driven off one shaft.

Stone grinding is still carried on to a great extent in distilleries, their aim being the highest possible yield of extract, irrespective of drainage. Special arrangements are provided in the side of the mash-tun or Kieve for running off the wort, level with the mash-bed; in the side of the tun a series of sliding doors are arranged which can be moved to suit the varying levels of the wort. Stone grinding in breweries is practically obsolete, inasmuch as the husks and grits are all powdered together, forming a dead mash in the tun, and thus preventing clarification.

We now turn to several designs of roller mills, which are at present working in breweries, and with which most of you will ho more or less familiar. The question of extract in the brewery has been discussed for some years by many eminent persons, but the question of the grist has not been thoroughly discussed, and it is the grist that I propose to make the chief point of my paper.

To obtain by the manipulation of the roller mill the greatest yield from malt in the brewery, a thorough separation of the husks and grits or semolina is required, but even with this the yield is again dependent on the plant being in thorough and efficient order, and everything connected with it used in the proper manner. Again, if the grist does not show a proper admixture of husks, grits, and flour, on which the yield is dependent, all efforts in the brewery will be of no avail, even with the best systems of mashing and sparging, thus pointing to the fact, which is becoming universally recognised, that more attention might well be paid to its composition.

As I have not heard of any authority for going into the composition of the grist, it may be that there is no recognised basis for working upon; but I suggest that the use of sieves in a small box, which I propose to describe later, might prove useful as a practical guide for the adjustment of the roller mill to give the highest possible extract.

To separate the grist by means of sieves gives a clear idea of the percentage of the component parts, and from the tables below, I give the results of tests on three different malts, giving four grades, namely husks, large grits Nos. 1 and 2, and fine grits and flour.

The sieves used were clothed as follows :—

These samples were passed through the Seek laboratory mill, because, being the recognised standard, I thought it would be the best basis for my experiments, and would serve as a practical guide for setting the brewery mill to give the same results.

It will be noticed that the three tests are quite different in composition, No. 1 test giving a low percentage of husks and a high percentage of fine grits and flour, while No. 3 test gives a high percentage of husks and a low percentage of fine grits and flour.

The difference might be due to excess of moisture, and if so, by taking the husks in the hand and pressing them they would have a tendency to ball. The sieves also act as a practical guide for determining the mellowness of malt, that is, the mellower the malt the higher the percentage of flour.

On examining the material from the different sieves, the coarse grits, on further reduction, were found to produce very little flour, and since they are of a vitreous nature they break up into smaller grits, while the fine grits from the lower sieve, being of a tender nature, produced flour on further reduction.

The two- and four-roller mills, if properly worked, give quite a suitable grist, and care should be taken to avoid the rolls running too quickly, which would result in injury to the husks, especially when the rolls were of large diameter.

Large diameter rolls are seldom used on account of the cumbersome design and unnecessary weight, and last, but not least, the amount of vibration set up by then; the standard diameters for rolls are 10—14 inches. Some of the malt mills I have seen in several breweries are so adjusted as to render thorn most unsuitable for economical use.

In the four-roller mill there are two separate breaks, and the rolls are adjusted so as to take the separate grades from the grading sieve, but, in practice, it is found that enough of each grade is not produced to fully feed each pair of rolls.

This clearly points to the fact that a certain proportion of the two grades must pass through one pair of rolls, and if these rolls are set for a fat malt, then some of the thin malt will pass through practically unbroken. If this be so, then grading is not necessary, it would be better to sieve out the dust and large substances, then pass the mixed malt on to each pair of rolls; but a few words on the adjustment of the two- and four-roller mills might prove of interest. Each pair of rolls should be set at about 1/32 of an inch in the nip, and a locking device arranged on the lever, enabling the brewer to adjust the rolls to suit the varying grades of malt.

The four-high roller mill, with scalping sieves between the first and second breaks, is next to be considered. 

The malt in this class of mill passes from the first cracking on to a small scalping sieve, which is kept vibrating by a mechanically driven tappet hammer, and so assists in extracting the fine grits and flour not requiring further reduction, which are passed along to the grist bin.

The husks, with the hard steely ends adhering to them, are then passed from the sieve to the second nip, and then on to the second scalping sieve for further extraction of flour, etc., while the husks are again (ailed off on to the third nip of the rolls, the troughs from the sieves mixing with the husks again as they pass along the shoot or conveyor to the grist bin. Unfortunately, this class of mill is very troublesome to handle, the adjustment being the chief drawback, and, bypassing the husks through three successive breaks, they get very much broken, rendering the mill practically unsuitable for brewery purposes, but useful for distilling.

The four-high roller mill has been somewhat modified, and this form presents many distinct features over the last mill mentioned, and by carefully adjusting the rolls, a uniform grist of any desired fineness can be obtained. The malt passing from the first pair of rolls falls on to the first sieve, which extracts the fine grits and flour, while the husks tail over to the second pair of rolls which reduce the hard steely ends adhering to them. From the second nip the husks then pass over a coarse sieve, which takes out all the grits and flour, allowing only then the husks, which are practically in their whole state, to pass on to the grist bin.

It will be noticed that the grits and flour from the coarse sieve fall on to a lower sieve, which takes out the flour and tails over the larger grits to the third nip of the rolls for further reduction. With this mill, it will be seen that a grist of four grades can be obtained and kept separate by the introduction of division boards, and at the base a sampling arrangement is provided, whereby a sample can be drawn at any time during grinding, and adjustments made accordingly.

There is a five-roller mill which is almost similar in the working to the last-mentioned mill, but the rolls are in two groups of three and two and are so placed to allow for a larger sieve for the thorough separation of the husks and grits.

There is a general tendency for mill manufacturers to introduce sieves in mills, even in flour milling on the break rolls, and the mill which embodies all the principles of modern milling both in design and output is that manufactured by Messrs. Seek Brothers, of Dresden.

The Seek mill has two pairs of rolls placed immediately above each other, and with a shaking sieve constructed between them.

It can be worked, either as a single mill by using the top pair of rolls only, or as a double mill by bringing both pairs into action.

When the top pair of rolls are used singly, they are set at a slightly finer crack, the crushed malt then following its usual course over the sieves, while the husks are tailed past the lower pair of rolls by the introduction of a sliding plate.

This is an important feature in malt milling, especially in the case of tender malts which only require cracking and separating, the length of travel on the oscillating sieves making a thorough separation of grits and flour which mix again with the husks in the shoot to the grist bin, but when hard flinty malts are being ground it is advisable to pass -the husks with hard particles of semolina attached on to the second or lower pair of rolls, which are set very close to ensure all the grits being reduced to a minimum fineness without the production of too much flour.

Messrs. Boby also kindly supplied me with a section of their two high malt mill, which is very neat in design and also very compact. The design shows that they have carefully guarded against explosions, which so frequently occur, and in some instances cause extensive damage.

The general principle of the mill is somewhat similar to the others mentioned, but instead of using an oscillating sieve to free the grits and flour from the husks, the ground malt passes from the top pair of rolls, through the explosion preventer, into a receptacle in which beaters are gently revolving.

These beaters serve the purpose of thoroughly freeing the husks of any particles adhering to them before passing on to the lower pair of rolls.

I have also a section of Messrs. Adlam’s latest design of mill, which might prove interesting, especially in the design.

In the section four rolls are shown, two of small and two of large diameter, ingeniously arranged to give three breaks, and at the same time the cavity formed by the grouping of the four rolls acts as an explosion preventer.

In this mill the two grades of malt which are cracked between their respective pairs of large and small rolls pass into the nip of the large pair of rolls, which are shown to be working together, and which, when properly adjusted, should give good results.

An arrangement of mills and sieves working in conjunction with each other, such as has been designed, would be more useful for the decoction system than for the English system of brewing.

In conclusion, if there is any point connected with the paper on which you desire further information I shall be pleased to answer any question.

The Chairman said there were two points which occurred to him as being very important. First, however complete and perfect a mill might be, it was very essential that the malt should be in a condition which in itself would ensure satisfactory grist. Sometimes even a poor kind of mill could produce wonderfully good grist if the malt was well conditioned. In the second place, they were all fairly familiar with the system of grading malts before introducing them into the mill; but he thought they would have gathered from the paper that that system was now challenged by another one which, instead of grading the malt, graded the grist. Milling had made wonderful advances in recent years, and it seemed almost incredible that modern milling, such as they knew it, was only invented 20 or 30 years ago. By way of illustrating the advantages of steel rollers, as compared with stone milling, ho mentioned that ho saw it stated in a book on the subject that the wear and tear of the stones was 3 or 4 feet in two years, whereas the wear and tear of steel rollers was only one-sixteenth part of an inch.

Mr. Callon said that it was true that a grinding stone lasted only about two years. They wore down to about 9 inches, and were then useless.

Mr. J. G. Wells inquired if there were any stone mills in use at the present time.

Mr. Callon replied only in distilleries.

Mr. H. J. Marriott said that he believed that where a stone mill was used, a man had to be employed who was experienced in keeping the grooves in the stones in order.

Mr. Callox said that that was so; it required a skilled man to do such work.

Mr. Marriott said that he thought that after being re-cut the grooves lasted only a short time.

Mr. Gallon replied that that would depend upon the hardness of the grain ground. The stones might run about a month before requiring re-cutting.

Mr. Marriott said Adlam’s mill contained two sets of rolls, but he would like to know what particular advantage there was in grinding twice without any sieving-out between the rolls.

Mr. Callon replied that he did not consider there was any advantage. On the other hand, he should say it was more a disadvantage, because, on the first cracking of the malt, the bulk increased by about 30 per cent. If they passed that increased bulk through another set of rolls, they would get a squeezing action. It would then produce more flour than was desirable in brewery milling.

Mr. G. Jones remarked that with regard to the two-pair roll malt mill the Lecturer suggested that the adjustment should be made with the lever. In actual practice, however, it was almost impossible to get fineness of adjustment with the lever; but with reasonable care it was an easy matter to got an exact adjustment with the screw.

Mr. Callon replied that the micrometer adjustment was fitted to roller mills only recently, and was used for adjusting the rolls instead of the lever. Once the lever was set in position the adjustment was regulated by the screw.

Mr. Wells pointed out that Mr. Callon had not indicated whether the rolls in the malt mills he had described were fluted or plain, or whether the machines contained one roll of each land. He would like to know which Mr. Callon considered to be the best arrangement, a pair of fluted rolls, or one fluted and one smooth.

Mr. Callon replied that on rollers where there was only one “cracking” he thought it was possible to have one roll fluted and one smooth; but where they had two sets of rolls, with two successive

breaks, it was possible to have them both smooth.

Mr. Marriott desired to know if experiments had been made with the sittings from the mill with the three sets of rolls, and if, where the grist had been so graded, it had been ascertained whether there was an increased or decreased extract?

Mr. Callon replied that tests had been made with the siftings, but the extracts were very high, and for that reason these mills were rejected, because they would cause trouble in the mash-tun and subsequent nitration in breweries, but they were useful in distilleries.

Mr. Richards said that Mr. Callon had referred to the fact of rolls working at different speeds, but he did not mention what should be the speed in an ordinary Seek Mill.

Mr. Callon said that he was afraid he could not give the exact figures; but, taking the mills he had seen, the average speed was somewhere about 650 feet per minute of the periphery.

Mr. A. H. Morris thought that the point to be aimed at was to get as large a proportion as possible of very small grit, and yet to keep the percentage of flour as low as possible.

Mr. Callox thought that the only way to get a large proportion of fine grits would be by having fairly coarse cracks between the rollers.

In moving a hearty vote of thanks to Mr. Callon, Mr. Wells said they would all be of one mind that such a paper as they had heard read was of particular interest to them as practical brewers. The review of the various machines that were at present in the market afforded some very valuable information. The brewer was generally limited to one machine, and in these days of financial stress he could not afford to “scrap” a mill with any frequency in order to try another one, and was therefore not in a position to speak from experience as to the merits of the different makes of mills. For this reason, such a paper as Mr. Callon had read was much appreciated; as it pointed out to them, in a succinct way, the respective value of the various mills now in use, and would, perhaps, make them consider whether they already had installed in their various breweries the beat type of mill. There were many factors in malt grinding which affected the results, and Mr. Callon’s paper helped them to understand, to some extent, the respective influences of those factors. He himself had an objection to the grist being knocked about more than was necessary, and had some little antipathy to the idea of screening after the malt had passed through the rolls. With regard to the Seek mill described, Mr. Callon assured him that the shaking action was very slight, and did not do more than dislodge the dust from the grits. Personally, he had always obtained good results with two pairs of rolls after grading the malt. Mr. Callon referred to the explosion preventer in Adlam’s mill, but did not say whether a similar arrangement existed on the Seek mill.

Mr. Callon replied in the affirmative.

Continuing, Mr. Wells said explosions were at times serious occurrences in a brewery, and were produced by causes which were not often easy of elucidation. He spoke of an experience he had of constantly recurring explosions, in which case the cause was proved to be the ends of the rolls grinding on the sides of the mill casing and so setting up sufficient heat to ignite the malt-dust. When, however, the rollers were properly adjusted there were no more explosions.

Dr. A. K. Miller, in seconding, said they were all indebted to Mr. Callon for so instructive a paper. It had been extremely interesting, and had been admirably illustrated.

The resolution was cordially adopted, and in a few words of acknowledgment, Mr. CALLON said he followed brewing as a hobby, and he was glad that what he had been able to say on the subject of Malt Mills and Milling had been so acceptable to them.

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