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.

Two surveys were done, one in 1943–44 and one in 1958–60, of the seasonal variation in the concentration of vitamin A and carotene in milk fat from 13 different areas in Great Britain. In the 1958–60 survey α-tocopherol and vitamin D were also measured. The main purpose of the second survey was to find out if the marked swing from Shorthorns to Friesians, and the trend towards greater use of carotene-rich foods in winter feeds that occurred in the intervening 15 years, had affected the pattern of vitamin A activity. In addition, monthly samples of butter were obtained in 1958–59 from a single factory in New Zealand during a complete butter-making season (9 months) and were assayed for vitamin A, carotene, α-tocopherol and vitamin D. Three experiments were done to study the effect of breed on the vitamin A and carotene content of milk fat, and in one of them α-tocopherol and vitamin D were also determined.

The seasonal trends for vitamin A and carotene were essentially the same in both surveys. A peak occurred in May after the spring flush of grass and was followed by a decline with a second peak in the autumn, except in 1959 when both the summer and autumn were very dry. Potencies were higher in the south than in the north, where the differences between summer and winter were more marked. In winter, mean vitamin A potencies of 5·8 and 7·7 μg/g fat were found for northern and southern areas, respectively; the corresponding values for β-carotene were 2·0 and 4·5 μg/g fat. Mean summer values were 8·8 and 9·7 μg/g fat for vitamin A and 5·1 and 6·5 μg/g fat for carotene, equivalent to increases of about 52 and 26% and about 155 and 44%, respectively, over winter values. Differences in mean potency between areas are explained by length of grazing season and type of winter feed.

The concentration of vitamin A in the fat was essentially the same for Ayrshires, Friesians, Jerseys and Shorthorns but somewhat lower for Guernseys; that of carotene was higher for the Channel Island breeds, particularly Guernseys, than for the other breeds studied.

Compared with this country, concentrations of carotene were higher and of vitamin A lower in milk fat from New Zealand, probably because of the predominance of Jersey cows in New Zealand herds. The seasonal trends for these vitamins were similar in both countries, but the spring peaks were earlier, the autumn peaks later and the summer declines more pronounced in New Zealand than in this country.

Concentrations of α-tocopherol in British milk fat showed a trend similar to that found for both vitamin A and carotene and were again influenced by feeding practices. Mean values of 23 and 29 μg α-tocopherol/g fat were found in the summer for northern and southern areas, respectively; the corresponding winter values were 15 and 23 μg/g fat. Mean values of about 30 μg/g fat were found, over a 28-month period, for the milk fat of each of the 3 breeds, Ayrshire, Friesian and Jersey. No seasonal trend was observed in the New Zealand samples; the mean value for the 9 months was 32 μg/g fat (range 24–39 μg).

Vitamin D potencies were higher in summer, when there is more sunshine, than in winter. The higher summer values in the northern than in the southern part of the country may have been related to a higher intake of vitamin D in the former from hay and pasture. Summer potencies of 0·44, 0·53 and 0·62 i.u. vitamin D/g fat, respectively, were found for Friesian, Jersey and Ayrshire milk; corresponding winter values were 0·06, 0·08 and 0·9 i.u./g fat. For the New Zealand butters, summerues values were higher than in this country, about 0·7 compared with about 0·4 i.u./g fat; winter values were similar in both countries.

The term stickiness, as used in the butter industry, refers to that property of butter which permits it to remain attached to solid surfaces. It is a phenomenon in which the components of force caused by adhesion and cohesion are inseparably involved and have been described by the term ‘hesion’. Hesion measurements of commercial samples of conventionally-made butter were much higher than those of continuously-made butter. The results of experiments on conventional and laboratory continuously-made butter from the same butterfat source indicated that the characteristic crystal structure influenced the hesion values. Homogenization of Gold'n Flow and conventional commercial butters markedly increased hesion readings. When nitrogen gas was added to pre-crystallized continuously-made butter the hesion values decreased with increasing gas content. However, there was an increase in the amount of butter which remained on the adherend when it became detached from the butter surface. Limited experiments on the effect of gas content in conventional butter also indicated that an increase in gas content resulted in a decrease in hesion values with more butter remaining on the adherend. The results of this investigation indicated that the crystal structure was responsible for the adhesive property of butter and the gas content influenced the cohesive property. It would appear, then, that both the crystal structure and the gas content play an important part in causing stickiness of butter.

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.

In a survey done in 1943–44 there was no seasonal difference in the riboflavin content of milk from 10 different areas in England and Wales that could have been associated with the change from stall to pasture feeding, and mean values were about 160 μg/100 ml for both the periods November-April and May-October. However, values for the 6 months August-January were higher (about 175 μg) than for the 6 months February-July (about 150 μg). Over a 12 months' period the mean riboflavin contents of Shorthorn and Guernsey milk from the Institute's farm were 142 and 191 μg/100 ml, respectively.

Proteinase systems of 3 strains of Staphylococcus lactis from Cheddar cheese have been studied. Proteinase of one organism was found in the culture supernatant, those of the other two were obtained in significant amounts only by disruption of the cells of the organisms. All 3 proteinases possessed maximum activity at alkaline pH (about 9·0–10·0). They were most active at relatively high temperatures (45–55 °C) and possessed temperature characteristics (μ) of 7000–8000 cals. Casein, ²-lactoglobulin and haemoglobin were hydrolysed by the proteinases; casein most readily and β-lactoglobulin more readily than haemoglobin. Because of their characteristics, such proteinases are considered potentially capable of contributing to the ripening of Cheddar 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.

A relatively simple method is described for the manufacture of Cheddar cheese under controlled bacteriological conditions. This method is shown to give the required degree of asepsis and to permit the manufacture of cheeses of uniform and normal composition.

The composition, bacteriology and flavour of 28 ‘aseptic’ cheeses and of 18 ‘nonaseptic’ control cheeses made by this method are discussed. Thirty-nine of these cheeses were made using singly 3 strains of Streptococcus cremoris and 2 strains of Str. lactis as starter and 7 were made using gluconic acid lactone in place of starter. The effect of inoculating the milk with a strain (25·2) of ‘Lactobacillus plantarumcasei’ and a strain (L1) of micrococcus was also investigated.

Whole acid casein and α-, β- and γ-caseins were isolated and treated with rennin. Chemical, chromatographical and electrophoretical analyses were done on the caseins and on the products obtained from them after rennin treatment. Three different fractions were obtained which had some specific protective activity for the Ca-sensitive forms of α-, β- and γ-casein, respectively, and which differed in their chemical, chromatographical, and electrophoretical properties.

It is suggested that each casein fraction in milk is associated with its own protective fraction which when released by the action of rennin, allows the casein to clot.

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.

A portable apparatus is described for indicating continuously as a measure of pulsation ratio the proportion of the cycle during which a liner is more than half open. With the machine set for milking, a probe with an electric switch which opens as the liner collapses is inserted in one liner, the others being closed with rubber bungs. The pulses of current from the switch are fed to a damping circuit so that the proportion of the cycle time during which current flows can be read on a meter. The problem of interpreting the various measures of pulsation ratio are discussed.

A new method is described for the determination of the free and masked sulphydryl (-SH) groups in heated milk and milk products. The procedure is based on the use of the specific -SH reagent p-chloromercuribenzoate, and utilizes another specific -SH reagent, 5,5' -dithiobis(2-nitrobenzoate), as an indicator producing yellow colours which are matched with the aid of standard glasses in the Lovibond Comparator.

The method was applied to heated skim-milks and a series of commercially prepared milk powders. Measurements were made in particular of the -SH content of UHT-treated milk. The changes in the -SH content of such milks on storage were studied; these changes could not be explained by a reversal of the denaturation of the whey proteins, although evidence was obtained that small amounts of heatdenatured whey protein can revert to the native state.

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 possibility of using a skin measurement as an index of potential milkproducing capacity in cattle was re-examined. Skin specimens were obtained by biopsy from 7 dairy herds, and each of 5 anatomical measurements was correlated with (1) milk yield and (2) butterfat percentage.

Only one of the pooled within-herd relationships was statistically significant. This relationship indicated that within the breeds studied, cows with the least hair follicle depth would be expected to give the highest milk yield. It is suggested that a more extensive investigation of this relationship might yield results of practical value in assessing milk-producing capacity and in progeny testing.

It is proposed that —N—P—N— bonds exist in casein and that these bonds can be hydrolysed probably at different rates by the action of rennin. It is proposed that the phosphorus is linked with the guanido group of arginine.

The effects of depriving cows of pasture, for part or all of a single interval between the morning and evening milkings, on milk yield and composition have been investigated. The yields of milk and solids-not-fat, but not of fat, were reduced. The characteristics of the butterfat obtained at the first 2 milkings following grazing restriction differed markedly from those of cows allowed to graze normally.

The changes observed suggested that the grazing restriction led to a temporary reduction in the supply of volatile fatty acids from the rumen and an increased utilization of fatty acids from body fat by the mammary gland.

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 vapour/liquid equilibrium coefficients for the steam distillation of indole and skatole from water solution over the range of concentrations 0·1 to 20–30 ppm. were found to be 2·4 and 4·7, respectively. The coefficient for indole in a cream containing 30% fat was found to be 0·31, and for skatole, in a cream containing 40% fat, 0·14. It is concluded that complete removal of indole and skatole contaminations from cream by use of steam distillation equipment is not commercially practicable.

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.

Casein derived from cow's colostrum contains 0·85% N-acetyl neuraminic acid and liberates 2·95% nitrogen soluble in 12% trichloroacetic acid (NPN) under the action of rennin. It therefore appears to contain a large proportion of κ-casein (calculated to be approximately 35%).

The smaller the micelles of casein in colostrum the larger is the amount of N-acetyl neuraminic acid they contain. Soluble casein, i.e. 25% of the casein in colostrum, contains 1·52% of this acid and gives 6·24% NPN under the action of rennin.

Casein and particularly the soluble casein of colostrum appear to be important sources of κ-casein and caseino-glycopeptide.