IGHT ON YIELD OF CHEESE

Taranaki Daily News, 15 July 1929, Page 14

IGHT ON YIELD OF CHEESE

INVESTIGATIONS BY A SCIENTIST EXHAUSTIVE REPORT SUBMITTED DISCUSSION BY DAIRY EXPERTS A comprehensive report discussing cheese factory yields and bher phases of the dairy manufacturing industry was presented > a special meeting of the Federation of Co-operative Dairy Comanies, in conjunction with the Dairy Factory Managers Assoeiaon, at Hawera on Saturday, by Mr.. P. O. Veale, scientist in charge E the federation’s laboratory. Cbnsideration is given in the first part of the report to the ictors having a true influence on yield, the composition of milk, ;s abnormalities and variations, fallacies with regard to experiments, moisture content and the difference between pasteurised and aw milk. j-f , Factors influencing the false, or theoretical, calculation of yield re discussed in the second portion of the report, showing how a igli yield may be obtained without improvement in the management or without any actual benefit to the supplier. Part-skim-ling is shown to have an influence on this aspect. The effect of ield upon the pay-out is also considered.

In accordance with the modern tenmcy to seek maximum efficiency, it lias icoine customary for the cheese-making idustry of New Zealand to devote conderabie attention to published stattics, and particularly to the figure ying the yield of cheese per pound ‘ butter-fat. This fact has resulted

i great rivalry between, neighbouring ictories in certain districts, and under ;ress of competition for more milk suply has given rise to a species of conjst which has been termed “the race >r yield.” By some persons the pubshed figure for the number of pounds f cheese made from each pound of but-jr-fat has been taken as an index 1 of lie efficiency of the factory, and not few suppliers have been attracted to ne or another company by the superior ay-out per pound of butter-fat which ccompanies a high yield. This paper is an endeavour to show

he very complex nature of the many inluences which affect the question of ield, and to show that, without a knowedge of all the attendant circumstances, ne is not in a position to make comarisons between factories, and may ven be seriously deluded by the figures hemselves. New Zealand cheese factories have universally adopted the pound of butterat as the unit in all calculations re-

atiilg to production, expenses and payments. In this paper, therefore, the term ‘yield” shall, in accordance with the travailing practice, be taken as meaning ‘the number of pounds of cheese made each pound of butter-fat contained n the milk used for cheese-making”; or Expressed in other words, “the ratio >f the' total cheese made to the total jutter-fat received.” Since it. will be shown later that the field may, by various devices, be raised or lowered, the term “yield figure” shall >e taken as meaning, not the true yield actually obtained, but the false yield apparently obtained as a result of the practices discussed. ■.The “milk cheese figure” will be used In the same sense as employed on company balance-sheets, namely “the number of pounds of milk required to make one pound of cheese.”

IFFECT OF COMPOSITION OF MILK.

The most obvious factor influencing yield, and the one which is best known, is the composition of the milk, particularly its fat percentage. Since the pound of butter-fat is used as the unit of payment, seme persons consider that * knowledge of the fat test of milk, is all that is required in order to determine ita cheese yielding capacity. This is not so. The basic factor determining yield is the ratio of casein to fat. Milks naturally having a low fat test have a larger ratio of casein to each unit of butter-fat than milk naturally richer in butter-fat, and for this reason normal low test milk yields more cheese per pound of butter-fat than normal high test milk. As an indication of the extent of these differences, and as tentative standards for cheesemaking under New Zealand conditions, the following figures are submitted. These figures are the averaged results of several hundred experiments and factory records with milks of varying fat tests, but are given only within the range likely to be encountered under fiverage factory conditions.

It is logical that New Zealand should get up its own standards for cheesemaking and that we should not expect to conform rigidly to the standards formulated by American authorities. For example, Van Slyke and Price, in their latest book on cheese (page 65), give a aeries cf figures which cannot be. accepted as standards for factory yields in New Zealand for the following reasons: (1) Dairy herds in the two countries are not the same. The Holstein-Friesian breed predomiiiates in Wisconsin cheesemaking areas, whereas the Jersey is the most popular in New Z-aland. Hence the average proportion of casein per unit of fat is different in the two countries, -and yields are consequently affected. (2) Van Slvke’s standards as quoted are artificial, ' for the reason that they are calculated .on the assumption that the cheese, from all varieties of milk has a uniform moisture content of 37 -per cent. This is never true in average practice. Chee-e made from milk testing

over 4 per cent, fat usually contains less than 37 per cent of moisture, and, the richer the milk, the lower the moisture content of the cheese. On the other hand, low testing milk makes up into cheese usually containing more than 37 per cent, moisture. (3) The standards quoted by Van Slyki are gross yields straight from the press, whereas New Zealand factory managers are concerned with the yields which allow for 14 days’ shrinkage.

(4) There is no guarantee that cheesemaking methods are identical in the two countries, and, if ><e are to believe the statements of critics, it would appear as if New Zealand cheese-makers employ some methods essentially their own. The fundamental reason for this difference lies in the fact that high testing milk contains a low proportion of casein to each unit of fat, the ratio fluctuating ■from'about 0.50 to a figure which rarely exceeds 0.65. Low-testing milk, however, generally contains not less than 0.65 parts of casein to one of fat, averaging over 0.70, and may even give a ratio in excess of 0.80. These proportions of casein t > fat are approximately the same in the different cheeses, and since casein is noted for its property of tenaciously retaining moisture, ample reason is adduced for the superior mois-ture-carrying capacity of cheese made from low-testing milk As a result Van Slyke’s standards for yield are, from the factory manager’s standpoint, flattering to milks testing much above 4 per cent, of butter-fat; but, on the other hand, do less than justice to the lowertesting milks. • ’ • ' On account of the dearth of published statistics relating to cheesemaking in | New Zealand, the figures. given in the last column are put forward as fair standards for New Zealand conditions,

since they represent average yields actually obtained when weights and composition of both milk and cheese were accurately known. Under normal methods of working the yields obtained over a whole year in cheese factories should . approximate to those given, or to others which follow, but any appreciable divergence from these standards must not be construed as evidence of error or inefficiency unless all the circumstances are

known. Special attention is here drawn to the fact that standards just quoted are based upon gravimetric fat tests. For reasons which will appear later, such tests may not exactly coincide with those given under the accepted factory procedure in New Zealand. A legitimate variation to allow for this recognised procedure is set forth in a later section devoted to a full discussion of the subject. ABNORMALITIES IN MILK. An important cause of loss to New Zealand cheese factories is the practice of adding water to the milk. Some farmers adopt this practice because they belike it prevents the rising and clotting of the cream; others add cold water during the summer months for the purpose of cooling the : ight’s milk; others believe that, in some way only known to themselves, they will profit by the procedure. - The factor- manager, however, condemns the addition of water to milk, not because the farmer is likely to gain, but because the factory is certain to lose. The losses occur in the following ways: —

(1) Direct losses in fuel costs, power and wages, caused by unnecessarily heating, handling and separating the total bulk of water brought to the factory. Many managers consider that complete elimination of water in the summer and autumn would frequently allow them to dispense with another vat, with obvious savings to the company. (2) Increased fat losses in cutting the curd, caused by the exposure of an unnecessarily increased surface area of the “watery” curd. (3) Greatly increased losses in solids due to the soft and . fragile nature of the coagulated milk and water. (4) Increased losses in whey butter, because every gallon of water which, in the guise of whey passes through the whey separators, carries with it as irrecoverable waste, not less than 0.06 to 0.07 per cent, of butter-fat. Thus every 100 gallons ui water amongst the milk of all the suppliers, will mean a daily loss of from 0.7 to about one pound of whey butter according to the efficiency of the whey separation. (5) The addition of water of questionable purity to milk is likely to be a cause of cheese-making difficulties. On many farms the water supply is not as pure as it should be, and the addition of water containing undesirable germs has been known to be a cause of manufacturing trouble and of lowering quality and yield. That the losses in cheese-making are not imaginary may be illustrated by the experience of one Taranaki manager who received, after an exceptionally rainy night, 30001bs of “milk” more than on the previous day, yet made 3 cheeses less; It will therefore be obvious that good yields are not to be expected unless the milk is practically free from extraneous water. Examinations of milk made

at the laboratory reveal that the practice still exists, and' thus that being unnecessarily lowered Furthermore, without continuous daily examination of the milk at any particular factory, it will be impossible to assess the effect of an unknown quantity of water upon the yield., NATURAL VARIATIONS. Evidence is not lacking to show that <»reat variations occur from day to day in the composition of milk, notonly _ with individual cows or herds, but also in the mixed factory supply in different districts. It is therefore fallacious to suppose that, if two factories, show the same average fat test, their yields must necessarily be similar. Neither is it co rect to consider that the factory showin" the greatest yield possesses the nignest standard of efficiency and workmanS 1U A P -study of the following table will indicate the scope of variations which actually exist. All of the examples are actual cases of mixed factory milk as supplied for cheese-making, a cn the drip principle, and therefore tiue samples of the final mixture as used in the vats.

For a proper understanding of the foregoing table, several facts must be borne in mind. ' Firstly, the ratio of casein to fat given in the final column is a measure of the cheese-yielding capacity of the milk; and the range from 0.57” to 0.67 is an indication of the varia-

tions which naturally occur. Under average circumstances, this range of casein ratios would account for variations in yield from about 2.66 down to about 2.40. The ratio of casein to fat is completely unaffected by the presence or absence of added water, and its fluctuations can thus be ascribed solely to natural causes.

Secondly, the fact that milk possesses a certain casein-fat ratio does not mean that it will necessarily achieve its maximum potential yield. Whether a milk is adulterated artificially or whether it is naturally poor in cheese solids, the fact remains that losses occur if an unnecessarily large bulk of liquid has to be treated. Reference to the column headed “Solids not fat” will show that very considerable •'-ariations occur in this figure which is generally assumed to be less subject to fluctuation than any other constituent of milk. Thirdly, the solids not fat very rarely fall below B.5C* per cent, at any time of the year in mixed milk of numerous herds'. Where the solids do fall below this tolerably low standard, we must face one or other of th. alternatives—either the milk has been watered, or the variation can be ascribed to natural causes. If we are to believe the solemn assurances frequently given by suppliers that no extraneous water .could possibly have been in their milk, we are left with the only other explanation that the milk was naturally deficient in solids. Whatever the reason, the deficiency is not without its depressing effect upon yield, and there would thus be ample explanation for poor yields experienced at the factories whose cases are cited. YIELD FROM INDIVIDUAL VATS. A consideration of natural variations in the composition of milk would not be complete without reference to the very variable and sometimes misleading re- • suits which are generally obtained when an endeavour is made to compare single ' vats of milk under ordinary factory conditions.

In the first place there is a universal tendency in such experiments for the results to be abnormally high, and apparent yields of cheese from 2.9 to 3.31bs per unit of butter-fat will frequently be encountered. Secondly, considerable variations occur in the performances of individual vats. To explain the general tendency for these individual vat results to be on the high side, we must observe that a single vat can hardly be considered as the factory in i iniature. The factory is subject to numberless incidental losses of milk and butter-fat in the shape of staff requirements, starter skimming, occasional skimming of late or poor quality milk, occasional spilling and wastage, all of which contain butter-fat and solids which are credited to suppliers but which do not eventually find their way into the cheese. As a result the average factory yield per pound of butter-fat suffers a depression when calculated over a period of any reasonable length in terms of the total butter-fat received into the factory. On the other hand, a vat which is the subject of experiment never undergoes any of the losses incidental to general manufacture. Every pound of milk recorded on the scales is carefully run into it. In general, the starter is added as an extra, and frequently its weight is not added into the total of the milk occupying the vat, on account of the popular delusion that no part of the starter is ever incorporated in the final cheese. In any case, the weight of butter-fat skimmed out of the starter used, should be included in the total amount upon which the yield of the vat is calculated (this being the method followed when the produce of the whole factory is being considered) yet the average experimenter never does so. It is therefore not remarkable that vat yields are so frequently higher than factory re-

A further point which accentuates the disparity between factory and vat results is*that very frequently, the cheese from the individual vat is weighed straight from the presses in order to complete the experiment. Thus the shrinkage which normally takes place in 14 days does not occur, and the yield is correspondingly inflated further if due allowances are not made. DIFICULTY.IN TAKING TRUE SAMPLE. Coming now to the variations which frequently occur between individual vats, wo may cite first of all the very real difficulty which exists in taking an ac-

curate representative sample out of a full 800 gallon vat. Even with continuous mechanical agitation, the fat still

rises to some extent, especially on account of the fact that the butter-fat in rich milk is often partially churned on its journey to the factory, and through the weighing machine, the pasteuriser and the chutes. To avoid the obvious floating butter-fat, the sample is usually abstracted from fairly deep down in the vat, and it therefore works out in practice that without a proper sampling tube capable of taking a number of fully representative cross sections of the milk

from top to bottom, the sample taken in the ordinary way from a full-sized vat very often fails to disclose the full amount of butter-fat contained in the vat. In consequence, the yield per pound of fat calculated in term of the butterfat disclosed by the false sample is frequently high, and is variable according to the degree of error involved in the sampling. This fact has been established by numerous experiments, and any one may verify for himself the finding that, in the majority of cases, a sample abstracted from a vat will appear to test 0.1 per cent, lower than the same milk, sampled upon the stage. As a concrete illustration of the effect of all the influences mentioned we

may quote the results of six individual vat experiments carried out in a factory which for the period when the experiments were conducted showed an average yield of 2.08 pounds of cheese per pound of butter-fat. The individual vat results over a term of three days were 3.07, 2.86, 2.92, 2.67, 2.84, 2.86, an average of 2.87 or 0.19 pounds of cheese per pound of butter-fat higher than the actual performance of the whole factory, with only a single result as low as the factory average. Furthermore, very considerable variations will always be encountered in the fat and casein, contents of adjacent vats. Even when the fat content appears identical, the casein content may show relatively wide divergences, thus producing different weights of cheese solids in the vats, and different moisture-carrying capacities in the resulting cheese. The very considerable fluctuations which occur in the composition and yielding capacity of milk from day to day are well known, and similar fluctuations occur amongst individual suppliers or groups of suppliers on the same day. Erroneous conclusions as to the yield-

ing capacity of milk will therefore frequently be drawn by observing individual vats on odd days,, and only by taking the average results over periods of not less than about ten days will these discrepancies tend to neutralise one another, and allow us to draw conclusions of value regarding the true average yielding capacity of the milk, and the standard of workmanship. Even then, allowances must be made before expecting factory returns to coincide with the averaged results of vat experb ments.

INFLUENCE OF BACTERIOLOGICAL QUALITY OF MILK.

A factor which may prevent a milk from achieving its maximum potential yield is the presence of deleterious organisms. Gassy curds are sometimes experienced, and the treatment which they require generally results in increased fat losses. Nou-acid milk may force the cheese-maker to keep his curd many hours over time in the whey; poor body results, and heavy losses are often experienced at milling and salting. Pep ionising germs may tend to liquefy the curd, thus causing a steady draining away of cheese solids during making, followed by leaking of the cheese and breaking down of the casein when upon the shelves.

The effect of undesirable micro-organ-isms upon yield is not as great as some of the more potent factors such as composition of the milk, but nevertheless is appreciable and must not be ignoied when comparisons are being made between factories. INFLUENCE UPON YIELD. It is popularly supposed that manufacturing losses play an important part in determining yield, and that high yields may be altogether explained by special skill on the part of the cheesemaker, whereby he is able to incorporate more solids and allow less waste than his fellows. In fact, according to the popular idea, milk is milk —the same

in all factories — and, • what a man gets out of it, is an indication of his ability as a cheesemaker. The first portion of this belief has already been proved to be erroneous, and the latter section will be shown to be true only in part. In the process of cheese-making, it is well known that in addition to the unavoidable escape of fat, other losses occur in the whey, owing to the escape of very fine particles of curd. These fine particles can be seen if a bucket, of clear whey is allowed to stand for a time, and the top part carefully poured off. It has been supposed by some, that if special precautions are taken to save these fine particles, an increase in the yield of cheese per pound of butter-fat may be expected. In order to achieve this purpose, the usual procedure advocated is to stop the mechanical agitators and to push the curd very carefully back from the gate of the vat about 15 to 20 utes before the time to run off. The contents of the vat are allowed to settle; the whey is run off very slowly so that no rush of liquid is occasioned; a channel is not opened down the centre of the curd, but drainage is facilitated from the sides, thus preventing any tendency to sweep the fine curd out; finally the whole of the whey is strained through a wire strainer and cheese-cloth, so as to retain every trace of solids. It is claimed that if this procedure is followed, the yield will be noticeably improved.

PREVENTABLE LOSSES LOW. If this statement is true, it implies that unnecessary losses were previously occurring. However, the standard of scientific knowledge and workmansnip amongst Taranaki and New Zealand cheese-makers is now so high that cases where preventable losses occur must oe few and far between. Efficiency is now so keenly sought and maintained by our factory managers as a body and opinions and methods are so freely' inter changed and discusse”. at conferences, that it would be difficult to discover a single item in which one first-class cheese-maker’s procedure is material y different from that of another. Gonsciously or unconsciously, the whole o the special precautions mentioned have been practised by careful managers tor years, and very little improvement in I this respect is possible. In fact numbers I of cases are or. record where special precautions have been advocated and pu into operation for. “saving” the “fine particles of curd,” without making t ie slightest difference in the yield of cheese. This statement must not be construct as a defence of carelessness. We a. know that careless cutting, violent agitation, Imperfect cooking, much dry stirring and generally rough, handling of the curd will certainly cause losses of seri-

ous magnitude, but methods of this kind are not practised by the best modern New Zealand cheese-makers. Instead, there is a widespread keenness to discover and put into operation the smallest innovation which would raise, even a trifle, the present high standard of workmanship. Analytical evidence may also be brought forward to prove that, on the average, the composition of whey from different factories in different districts is very similar, and that losses are of the same order of magnitude. Up to the present, it has been found impossible to demonstrate any constant difference in composition between average samples of whey from high and low-yielding factories. The following are typical figures, and are averages of a number of samples: WHEY ANALYSES, SEASON 1927-28. Total Fat. Casein. Solids.

Variations in the fat content of whey are fairly common, but as the fat is recovered by separation, they are not such a serious loss to the company. On the other hand, the casein content,- and therefore the solid curd content of whey has always been found singularly constant, and apparently irreducible. In passing it may be mentioned that the above casein losses are only about half the figure stated by Van Slyke and Price to represent the average loss under American conditions. As further evidence that the so-call-ed saving of the fine curd is mainly illusory, we may point to the fact that, even when the whey is strained through several thicknesses of cheese-cloth, the same fine flocculent precipitate will be found to separate out on standing. The action appears to be a physical ..one caused by the cooling, and the material which settles out is so immeasureably light that it could never be retained, and, in any ease, its separation makes no apparent difference to the composition of the whey. Samples of clear whey have been analysed, and, after settling has occurred, the top liquid has been carefully poured off, and an analysis made of the turbid liquid at the bottom containing the so-called fine particles of curd. The following figures are typical examples coming incidentally from a low-yielding factory:— Total Fat. Casein, solids.

Orminal clear % v hey 0-33% 0.04% 6.38% Cloudv whey from bottom 0.25% 0.04% 6—8% From these figures it would appear that the fine sediment which separates out has no significance from the cheesemaker’s point of view. It was originally in a very fine state of suspension in the warm whey, and is deposited by coolin" 1 It consists neither of fat nor of casein, and there is no measurable difference in composition between a clear sample of carefully run whey and a may therefore conclude from the foregoing that the large majority of our cheese-makers are about on a par in incorporating in their cheese every available ounce of material coagulable by rennet, and that claims to high yields through the “incorporation of extra solids” have no foundation m fact. After discussing the effect of yield upon the pay-out in the second portion of the

report, which will appear in to-morrow's Daily News, the scientist concludes:— Expressed in its simplest form, it is manifest that four pounds .of butter-fat at Is 6d are equally as valuable to the farmer as three pounds of fat at 2s. The

higher price, however, creates the impression of superior efficiency and great desirability, and may attract suppliers who ar« unaware that it may not necessarily pdt » penny more in their pockets.

(To be Conelrd'-fD'

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Factory A High yield (Nov.) 0.26 0.050 6.53 Factory B Low yield (Nov.) 0.26 0.050 6.4G F.x;tory B Low yield (Dec.) 0.25 0.047 6.2 1