MILK FOR CHEESE TO MAKING

Stratford Evening Post, Issue 3, 12 September 1927, Page 8

MILK FOR CHEESE TO MAKING

METHODS OF TESTING. MEKJTS OK AUGHOSCOPICAL EXAM IX ATI ON. lecturing al Stratford on Friday alternoou oil “Tina i no; Iho Quality ol' Milk lot - (Aieeso-Making,” Air. P. O. A calc, scientist ai. the Ha worn, laboratory of the Federation of Dairy !' actories, said lio designed to traverse, as far a.s possible, file majority oi tlie tests whh h had been published up to the present, aiming at giving some insight into the bacterial quality ol milk. Cheese-makers were always on the look-out for rapid tests which would enable them to tell good from had milk on its receipt at the factory. Generally the rapid tests were not satisfactory. They could be curried out in a laboratory, but not in a factory. The aim ol’ lire manager was to bo able to determine what fort ol produce certain milk will yield. r l lie problem of testing the finality of milk for cheese-making w'aa vluTercnt to that of testing cream for butler-making, hccau.se in the case of cream if generally stood lor some time before corning to the factory and the bacteria had time to develop*- Unfortunately (extravagant claims had been made for some tests, and some of the claims had not been substantiated. (I TIDE TO ‘MANAGERS. Mo hoped his remarks, therefore, .would act as a guide to managers in their reading regarding tests. Otherwise managers might ho misled by the unfounded enthusiasm of the writers. The simplest test was that of smell and taste. It was not a very valuable test, though it was useful iu detecting extreme oases. Milk with acidity and flavours could thus be detected, but there were faults which could not he detected by tins means. . Feed flavour could ho detected, and the ill effects of feed flavours became worse as the processes of manufacture proceeded. The most undesirable features —gas formers and peptonisers—could not ho detected by taste and smell. The aridity test, used at condensed milk factories was more suitable for advanced cases, and was not very reliable when the test was made daily, as it was at a cheese factory. Milk could be advanced in acidity as a result of the use of starter and still be good, for cheese-making, while if tlie acidity arose naturally the milk would not be good. In tlie sediment test a sample of milk was forced into a tube through a disc of cotton wool, impurities being left on the disc., CLEANER- MILK. It these discs were displayed at the factory tlie suppliers with clean discs would “chiack” those with dirty discs and the tendency would be towards cleaner milk. The test was valuable as it gave a clear demonstration to suppliers of tlie dirt contained in their milk. It was the general experience that suppliers quickly responded to a little gentle persuasion when applied iu this form. The test only showed the extraneous dirt, but this was tlie chief cause- of gas-lormers and peptonisers. If the dire wa s reduced so would the pasformers and peptonisers be. The test had a. few limitations, which should he emphasised. The test could be evaded by careful straining on tlie part of tlie supplier. In the Wellington municipal supply it was found that the test was being evaded by straining their milk through cheese-cloths. Hut though the cheesecloth would take out the dirt it did not catch the bacteria l arising from the dirt, which would pass through any general filter. The sediment test would not indicate milk of poor keeping quality arising from defective cans, etc. Milk might give a clean disc and still produce poor cheese.

THE A LCOH'OL TEST. In tile alcohol tost, which had laud-, ed out of all proportion to its value, • milk was mixed with alcohol in a test tube, and in the case of had milk, granules wore formed on the tube.; To a 1 certain extent the test would detect mammitis milk and it was valuable in detecting the farmer who persisted in mill-ring cowg which were in poor health. However, lie thought that what the alcohol test showed could he found by managers by much simpler means. For detection of mammitis microscopical Examination was the best- The alcohol test was not valuable where it was touch and go. In the alizarol test, alizarol powder was mixed with alcohol and placed in the milk. The originator bad prepared a shark of the different colours which would result when the test was applied to different milks,! tlie colours varying with the amount of acidity. The difficulty of the manager memorising the mam- colours was a disadvantage, and the test was only valuable in a. limited number of; cases. It was likely to give reliable results in only of) pet cent, of obvious cases. Therefore it was not worth developing from the manager’s point of view.

THE POILIXG TEST. I There was also the boiling test. If milk was high iu acidity it would . coagulate before reaching boiling point, hut in such a ease the .manager would detect the quality ol the milk by the smell. The presence of calostrom could lie detected il granules were found when the milk was istrained. The rennet test wa-jj used < largely iu America, and the maim- 1 ger, no doubt, could adopt some lorm ■ of it.. If a sample of milk was taken j and rennet, was added in the proper- | lion of 'lows to UiOGih of milk, it | should set in 30 minutes. ]]y this means the manager could detect the j supplier who was sending the milk which wa : s hard to set- it seemed, that nobody had yet hit on the right reason why certain milk at certain | seasons refused to coagulate. The ; only remedy was to exclude such milk. 'fhe Roducta.co test, was o? wide application. Methylene blue j was a ided to milk, which was brought j to blood heat, and a note wa,s made j of tlie time it took for the Hue col- | our to disappear. The more banter- j ia, the quicker the colour disappeared, i The best milk would retain the col- ! our for over live hours. j QUALITY, NOT KIND. In second-class milk the colour lasted from five to two hours; thirdclass retained the colour from two ; hours to half an hour; and fourth-j class lost ills colour under half an

hour. It was urged against this 1 t<Vt that it told the quantity of bac- | tcria and not the kind, though it was most important to know the kind. Aiilk which lost the blue colour quick- | ly was infallibly found to contain much harmful bacteria. This test i detected the presence of pus cells and this was a valuable feature of it. It was also, valuable in that it was quite impossible for good and bad milk to give the same result. In the fermentation test the milk was kept warm for 21 hours, when the bacteria developed and the manager could tell the character of the milk. The formation of whey indicated the poor milk- A limitation wu.s that, one must exercise great care if one was to rely on the fermentation test alone. The methylene blue test could he carried out in conjunction with the fermentation test, and the blue would determine the worst milks. The blue did not. interfere with the fermentation. PEROXIDE TEST. Hyrogen peroxide could he used in testing. As tlie peroxide destroyed the bacteria oxygen was liberated. The oxygen being collected, the quantity of if indicated the number of bacteria there were in tlie milk. This test was valuable in the laboratory but was not convenient for use at flie factory. The bromin-creasole test had been extravagantly praised, but it was expensive and ,so delicate that it could be upset by outside influences. The microscopical counting of bacteria might he regarded as a laboratory test, but tie thought it could easily be carried out at trie factory. He thought the time was coming when all managers would be supplied villi a certain amount of apparatus, including a microscope-. The operator saw the bacteria under the microscope and actually counted them. Six tests could be carried out on one slide. The sample was stained with methylene blue, and theft immersion m methylated spirit took out the colour except on the bacteria. In actual practice, tlie manager would not need to actually count the bacteria., because lie could see at a glance tlie quality of the milk- In tlie highest quality milk there were only a few bacteria; in the medium class 6 to 2o would he iseeu ; and in the case of poor milk there would he hundreds of them.

A SIMPLE TEST. The test was simple to carry out and it could be done in the factory; and it enabled one to find out what was wrong with the milk. If mammitis was the trouble pu s cells would be found; if the trouble was due to dirty machines clumps of bacteria would be found; in the case of dirty cans there would be a film; and if there was exterior contamination the rod formation was prominent. It was a very valuable test a»d one that it would repay managers to cultivate. Directors would make a good limfositmeirt if .they fborj-) t Imiiqr'oscopes for their managers. It was easy to learn how to make the test and the results were very valuable. The result could he got in five minutes. An important feature was that the test bv microscopical examination could not bo evaded by straining or by the use of preservatives. Carefully strained lyilk could pass the sediment test,, but would be detected by the microscopical examination. Concluding, Mr Veale said some of the tests mentioned had limited ap>plieation and gave doubtful results; some were valuable for special purposes j and some were valuable if their limitations were well understood. The microscopical examination test, however, left very little scope for argument, and it could be very easily demonstrated ; and ho felt sure that shortly it would be generally used.