a—29.

111. DAIRY BACTERIOLOGY. Report of G-. F. C. Morgan, Dairy Bacteriologist, Wallaceville Laboratory. Serious problems have arisen in the past year, the most important of these being the discoloration of annatto-eoloured cheese. The groundwork of this investigation has been successfully covered, and the problem will now be further investigated in co-operation with the Dairy Research Institute, Palmerston North. In addition to this, very comprehensive work, has been carried out on methods at present practicable for the examining of cheese-factory suppliers' milks as regards suitability for cheese-manufacture, and also on the various types of milk received at cheese-factories. This work has included the testing of nearly 1,000 samples of cheesefactory suppliers' milks from the Wairarapa, by the following methods : — (a) Plate count. (b) Gelatine count. Count of putrefactive types. (c) Reductase test. (d) Curd test. (e) Acidity-development— (1) By direct titration of samples at two-hour periods holding at 98 degree F. (2) By pH development in broth, watched at one-hour periods. Considerable variation has been noticed in the behaviour of suppliers' milks, and, where possible, the bacteriological causes have been investigated in detail. Examination or Cheese-colouring. A new branch of work was undertaken in the past year in the examination of samples of cheese-colour for the presence of lead. The decision to carry out this work resulted from the discovery of lead in samples of cheese showing black-spot discoloration, and the finding of lead in appreciable quantities in the colouring used in the manufacture of this cheese. This work was confirmed, where possible, by the Department's Chemistry Section at the Dominion Laboratory, Wellington. Experimental Work in the Dairy, In connection with the work carried out in the experimental dairy thirty-two cheeses were manufactured by Messrs. J. B. Sawers and M. Syron, Dairy Instructors. The experiments included the introduction of cultures of organisms isolated from discolored cheeses, the addition of iron oxide, and the effect on cheese of milli produced by cows grazed on paddocks recently topdressed with sulphate of ammonia. Investigation of Discoloration in Annatto-coloured Cheeses. The following types of discoloration in cheese have been brought to the notice of the Laboratory during the past year: Bleaching; muddy discoloration through the body of the cheese; black-spot; red spots; a faint pink and purple discoloration. Bleaching.—The investigational work into this defect was commenced in the early part of 1930 with the reception of a number of samples of bleached cheese which were examined in a number of ways, and from which a number of organisms apparently predominant in bleached portions were isolate.d. These included mould cultures of penicillium and aspergilli, also cultures of yeaSts (not lactose fermenters), together with various types of bacteria. A number of cheese-samples showing a very marked muddy or dark discoloration were also received. Cultures were isolated from bo,th bleached and dark discolored cheeses, and introduced into experimental cheese as washed cultures at the time of hooping. Cultures of as many representative types as possible from bleached portions of cheese were added to tubes of sterile milk containing annatto. It was found that several cultures were capable of reducing the colour of annatto, but never to the extent to which it is reduced in a bleached portion of cheese. Again, cultures were tried out on annattoed milk-agar. In this case a yeast found present in a bleached area was found to cause a possible bleaching, but to no depth. It was noticed that where certain moulds and yeasts had been able to develop under the wax a marked bleaching had developed in inoculated proprietary cheese. At this time cultures of penicillium mould were introduced in!o the cut surfaces of experimental cheeses about three weeks old. Mould-growths developed from these cultures which were kept at roomtemperature and in the dark. Cutting and examination of these sections at the end of one month after inoculation showed a very marked bleaching to a considerable depth. At the same time that the investigations on bleaching were being carried out specimen samples of cheese showing dark discoloration were received. Blach-spol Discoloration. —In one case, that of a sample of cheese received from .... Factory, a definite small local area of dark discoloration was seen, having a darker nucleus at its centre and not associated with slits or openness in the body. References were made at this time to Professor Leitch's (Kilmarnock) work on dark discoloration in cheese, and, after cultural work had been completed, examination by Fairhall's analytical method was carried out on the ash of the discolored local area for lead. After thorough trial of the test against blank controls and also tests for the purity of the reagents used, a definite positive result for lead was obtained, and a further portion of the sample was taken to Wellington and examined at the Department's Chemical Laboratory, where the presence of lead was confirmed. Together with this sample of cheese; a sample of annatto was received from the dregs of the drum in use at the same factory when the cheese was made. An examination of this annatto was made by Fairhall's method, and showed the presence of lead in considerable quantities, which could also be determined by a qualitative chemical examination of the ash. Bacteriolical plate cultures from the cheese showed that there was a considerable number of organisms belonging to the proteus group present. This group has the ability to cause blackening in any medium containing lead. Shake cultures were then made introducing this organism into annattoed milk-agar containing

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