Live Stock and The Farm.

Southland Times, Issue 22131, 27 September 1933, Page 15

Live Stock and The Farm.

GRADING OF MILK METHODS COMPARED. OPPOSITION TO CURD TEST. Apparently the controversy over the new dairy regulations, as they relate to the method of grading milk for cheese-making, is to end fruitlessly, as far as the opponents of the curd test are concerned. The position as it exists now, and as it is likely to continue, is wholly unsatisfactory, not particularly because the curd test has been chosen, but because the case made against it by highly qualified opponents has been so inadequately answered by those responsible for its adoption. We have heard the criticism that the curd test is a relic of an ancient day and of a manufacturing technique which no longer obtains, and we learn that it has been decided upon in spite of the wholesale condemnation heaped upon it by scientific opinion outside the Department of Agriculture’. If the department had any bulk of scientific opinion behind it in its decision the exception taken to it need not have created any great concern. Since modern scientific knowledge both here and abroad is almost wholly ranged against it however, concern that the best is not being done for a vital industry must be a natural consequence. Nothing the Minister of Agriculture said at Hamilton the other day in reply to Mr P. 0. Veale's definite and detailed charges could be construed as being worthy of the final acceptance of the industry as a whole. He has taken an almost isolated opinion in preference to the majority view of the most competent scientific authorities of the day. His conspicuously brief reply to the criticism this circumstance has occasioned has included no argument which could possibly justify his action. If he has said all he can on the subject he must not be surprised if there is a lack of confidence in his decisions or in the opinions of his advisers, states the Auckland Weekly News.

As is well known, the curd test, to which such strong objection exists, briefly entails the taking of a sample of milk, adding rennet, and then examining the resultant curd for flavour, gas and texture. A heavy responsibility is placed upon the senses of sight, taste and smell, and while experience could doubtless ensure a fair degree of accuracy in the testing, it is obvious that there could be no guarantee of infallibility. Opponents of this system agree on the efficacy and desirability of either the microscopic test or the methylene blue test, either of which reduces the chance of fault through human error, and both of which fulfil the more exacting demands of modern requirements. The microscopic count is not suited to the analysis of pasturized milk, since the bacterial cells killed in the heating process cannot be distinguished from those which survive. A small quantity of milk is spread over a definite area on a clean microscopic slide, and is dried, treated and stained for the purpose of rendering the bacteria more clearly visible. Observed under a powerful microscope the bacterial cells visible in a number of different folds of the microscope are counted, from which the number of bacteria in one cubic centimetre is estimated. However, it is rarely necessary for the analyst to make actual counts of each supplier’s mill:, except where the sample appears to be on the borderline between grades, so that a large number of samples can be analysed in a day and each given a grade lying between definite limits. The methylene blue test is based on the fact that bacteria are able to reduce the dye, when added to the milk, to a colourless form. The more bacteria there are in the milk the sooner will the colour disappear, so that from this a definite indication of the quality of the milk can be obtained. Very bad milk becomes decolourized in 20 minutes or less, and according to a standardized formula, is apportioned an exceptionally heavy bacterial content. The time of decolourization ranges up to over 5J hours in the case of the best milk.

The value of the microscopic test lies not only in the efficiency with which germs can be detected, but also in the fact that their probable source—whether from udder trouble, poorly sterilized utensils or insufficient cooling—can be indicated, and that it provides a means of discovering early and certainly the presence of mammitis in a herd. Though it might agree to a fair extent with the microscopic test in grading results, the curd test con not compare as far as these invaluable indications are concerned. The scientist tells us that in certain cases milk may be proved free from germs and make up into good curd. In other cases milk may be found to contain large numbers of undesirable germs and will not make up into good curd. In such cases, which are perhaps in the majority, the two tests agree. But in some instances good milk, free from germs end clean in every respect, might contain a feed flavour, or because of the artificial conditions of the curd test, might develop gas or soft body and be graded down. In other instances bad milk, with a high germ content, and coming from badly cleaned machines or cans, or containing whey organisms, might give rise to a curd which looks and smells good and be graded accordingly high. In such cases the curd test certainly does not agree with the microscopic method.

It should be unnecessary to have to argue that a seemingly satisfactory curd containing large numbers of unknown germs is not the best for cheesemaking, and that very likely the product will develop unexpected faults in flavour, texture, and colour as it matures. With the microscopic test the cheese-maker would know, in such that although the product might at first appear to be ‘finest grade” it would probably not be so satisfactory by the time it had matured. It is in the light of such knowledge as this that the new grading regulations must be judged. The controversy over the method which should have been adopted is one in which only the qualified scientist is entitled to express an opinion. The wisdom or otherwise of the Minister’s decision must be determined on the dual basis of the competency of his critics and the generality with which the body of modem science supports their views. From this standpoint there can be little doubt that a grievous mistake has been made.