Butter made from good quality sweet cream is usually free of any major defect in flavour, even after a long period of cold storage. However, butter made from cream ripened with starter, is liable to develop oily and fishy flavours during storage. Thus the manufacture in New Zealand of butter for export has been confined to the sweet cream product.

The results reported suggest that it is possible to follow the ripening of Parmesan cheese by means of histochemical reactions for proteins, glycoproteins, acid mucopolysaccharides and lipids containing choline.

The blue colour, formed when the proteins of the curd were stained with Bonhag's reagent, slowly turned to violet and then to red as ripening progressed.

Glycoproteins and acid mucopolysaccharides, although present in very small amounts, appeared to be a constant characteristic of the cheese.

Lipids containing choline, which were absent from the curd, were clearly visible in 3 to 7-month-old cheese. They then decreased and were absent in the ripened cheese.

Fink (1954) and Fink & Schlie (1955a) fed rats on a diet intentionally marginal in vitamin E and the sulphur-amino acids, in which dried milk supplied the protein (10%). They were able to relate the development of fatal liver necrosis in rats to heat damage of dried milks. Using their method, no liver necrosis developed in our rats with 2 spray-dried skim-milks, evaporated milk and milk subjected to ultrahigh temperature treatment, with or without subsequent in-bottle sterilization. With a roller-dried skim-milk sent to us from Germany by Fink and found by him to be of ‘middle degree necrogenity’, no liver necrosis occurred in hooded or albino rats bred in our laboratory, but the lesion developed in albino rats from an outside source. It was found that this milk had a lower selenium content than 2 British spray-dried milks. With rats given a necrogenic diet, differences were observed between and within strains in their susceptibility to liver necrosis and in their ability to utilize dietary selenium.

Butter made from cream separated from milk accumulated in a refrigerated tank from morning and evening milkings for 3 days was compared with butter from similar milk unchilled and separated and pasteurized for churning daily.

When the milk was of good quality there was no difference in the butters either when fresh or after storage for 4 and 8 months.

When the milk was of poor quality the butter from the chilled milk was superior in flavour, both when fresh and after storage, to the butter from the unchilled milk. The defects in the butter from the unchilled milk were probably due to bacterial growth in the milk during the short period of holding of the unchilled milk.

The ‘mushroom compound’ previously reported as a gas chromatographic fraction of oxidized dairy products has been identified as oct-l-en-3-ol. The alcohol was found to have a flavour threshold value of 1 part in 109 in water, 1 part in 108 in skim-milk, and 1 part in 107 in butterfat. A mechanism for the formation of oct-1- en-3-ol is discussed.

The presence of a thermolabile inhibitor of coagulase-positive staphylococci in milk was confirmed. Starter streptococci significantly suppressed the multiplication of staphylococci in milk not only by their acid production but also by some other competitive effect.

Cheesemaking trials showed that staphylococci multiplied considerably more rapidly in ‘slow’ or ‘sweet’ cheese, where the starter was inhibited by phage, than in normal cheese. Little decrease in numbers occurred in ‘sweet’ cheese even after 18 months, in contrast to the rapid decline in the normal cheese.

Staphylococci subjected in the laboratory to sublethal heat treatments had a prolonged lag phase on all media and their % recovery on selective media was significantly lower than on optimal non-selective media. It is suggested that the low survival rate of the staphylococci in cheese made from milks heated at sublethal temperatures is due to the lag in recovery of heat-shocked cells and their inability to multiply in the unfavourable cheese curd.

The infra-red, absorption of milk and its main constituents has been recorded and it has been found possible to determine quantitatively the fat, protein and lactose contents from measurements of the intensities of the respective absorption peaks at 5·73, 6·46 and 9·6 μm. Solids-not-fat (SNF) content can be obtained from a single intensity measurement at 7·9 μm where the fat shows no attenuation and where the protein and lactose extinction coefficients are approximately equal. Photometric errors due to natural variations in fat globule size distribution can be eliminated by prior homogenization. Based on these observations, an automatic infra-red milk analyser (IRMA) has been constructed, which can determine the fat, protein, lactose and SNF in a pre-warmed milk sample in under 1 min. Preliminary tests carried out on 50 milk samples from individual cows, representing 3 different breeds, gave standard deviations from the chemical analyses for the percentages of fat, protein, lactose and SNF of 0·10, 0·07, 0·07 and 0·19, respectively. The standard deviations for the percentages of fat and SNF on 60 farm bulk milk samples were found to be 0·08 and 0·12.

Following enzymic digestion with pronase, masked SH groups in micellar casein became available for titration in disaggregating media with mercurial reagents. The content of cystine and cysteine was also estimated after reduction with (a) sulphite, and (b) borohydride, and also by reaction in alkaline conditions with Cd(OH)2. The results show that the micelles contain mainly cysteine, and that it is likely that cystine is not present.

A method was devised for separating proteins of skim-milk on Sephadex G 100 dextran gel. Four fractions were obtained, the first 3 corresponding to casein micelle, lactoglobulin, and lactalbumin fractions while the last contained no protein. The fractions were examined using starch gel electrophoresis, and results are also given for the average composition of the fractions. Differences between the composition of the casein micelle fraction and that of sodium caseinate made from the same milks are reported.

In an endeavour to find an ideal medium for the isolation of the bacteria from Cheddar cheese 10 media were compared. The initial criterion was of ability to yield maximal counts with each of 23 representatives of species common in Cheddar cheese. Subsequently the more promising media were compared for ability to give the highest counts for cheese emulsions without obvious distortion of the proportions of the various species present.

Since no one medium gave maximal counts with all strains, two complementary media of quite different composition are suggested for the bacteriological examination of cheese.

A method is described of measuring pressures in a teatcup assembly using strain gauge transducers and simultaneously following movement of the liner wall by means of a cine camera. In preliminary experiments with a narrow bore type liner it was found that pressures below the teat could vary during a single pulsation cycle from a few inches of mercury below atmospheric pressure (inHg vacuum) to as high as 25 inHg vacuum in the absence of an airbleed. Bleeding air into the barrel of the liner or into the clawpiece considerably reduced fluctuation in pressure, and the vacuum barely rose above the nominal milking vacuum of 15 inHg. Reducing the rate of change of pressure in the pulsation chamber did not greatly affect the maximum vacuum obtained. Opening and closing of the liner by pressure change in the pulsation chamber was under some conditions considerably delayed by the pressure conditions existing inside the liner.

It is suggested that inertia effects of milk in the cluster and the natural frequency of the system are largely responsible for the observed pressure changes under the teat.