Five hundred and sixty-nine individual cow milk samples from forty-five cows in a single herd were analyzed for fat by the Gerber method, and solids-not-fat by a standard gravimetric method and by the two commonly used British hydrometric techniques. Three hundred and four of the samples were analyzed also for lactose, protein and ash. Large differences between the total solids values obtained by the hydrometric and gravimetric methods were recorded. The magnitude of the differences from the gravimetric values varied with the season of the year and the stage of lactation. The main factor affecting the differences was the protein content of the milk, and equations for the calculation of total solids content incorporating a protein correction factor are given for use if the protein content be known. The hydrometric methods are considered to be of limited use when applied to milks of individual cows.

The crystal habit of milk fat is determined by the cooling procedure employed and is changed markedly by interesterification (randomization) of the fat. X-ray diffraction analysis indicated that slowly cooled milk fat occurs in both beta prime and beta modifications, whereas in rapidly cooled milk fat, evidence for the beta prime modification only was obtained. The long spacing was greatly increased by interesterification, especially when the fat was slowly cooled. The presence or absence of certain high melting glyceride fractions greatly influenced solid fat content, softening point and hardness of milk fat.

Using an experimental method of half-udder comparisons the effects on the amount of residual milk of varying milking intervals, the duration of milking, and the delay between the stimulation of milk ejection and the start of milking were measured. Yield of residual milk was not related to the length of milking intervals within the range of 4–16 h but the butterfat content was directly related to the length of the interval. Neither the yield nor the butterfat content of residual milk was affected by a change in the duration of milking of 1 min. A delay between the stimulation of ejection and the start of milking of 6–8 min resulted in increasing the yield of residual milk by about 1 lb.

It is suggested that these results indicate that milk ejection is sufficiently persistent that residual milk is unlikely to be affected by delays between stimulation of milking and the start of milking until they exceed 4–6 min.

Details are given of a method, based on the peroxidase activity of the sedimented erythrocytes, that is suitable for the quantitative estimation of blood in milk.

Fat and carotene oxidation in Cheddar cheese may give rise to bleached areas surrounding slits in the cheese and to a tallowy flavour. It was shown that direct contact of the fat with atmospheric oxygen was essential for oxidation to occur, and examination of cheeses showed that slits running from the rind into the interior provided this contact. Factors enhancing slit formation such as gas production by bacteria and mechanical shock to the cheese were shown to increase the incidence of tallowy discoloration. Factors which tended to exclude oxygen such as waxing the cheese surface, wrapping the cheese in plastic film or sealing in a tin were shown to reduce the incidence of the fault or eliminate it.

Accelerating factors were shown to be low cheese storage temperature, excess moisture in the cheese and possibly low salt content. Various factors which may be relevant to a commercial cure for discoloration are also discussed.

Unwrapped samples of salted sweet-cream butter were stored in darkness at 1°C for 6–8 weeks over silica gel, water, isotonic salt solutions, and in free air. Moisture and fat peroxide gradients from the surfaces to the interior of the stored samples were measured in thin sections obtained by a simple macrotome technique. The surface oxidized at the same rate as the rest of the butter and its rate of oxidation was not affected by moderate drying or moisture uptake. With severe surface drying, especially when induced by silica gel, fat oxidation was inhibited, while moisture uptake by the more heavily salted butters promoted surface oxidation.

Friesian cows averaging about 30 lb of milk daily, were used for nitrogen balance experiments of the change-over type, in which 3·0–3·5 lb of two mixtures of molasses and urea were added to basal diets low in protein, but containing a high proportion of starch and lower carbohydrates, and ample energy for the amount of milk produced. The molasses mixtures contained 9–10% urea, about 2% H3PO4 and were added either alone or with 7% ethyl alcohol.

In the first experiment, with three cows, the intake of digestible crude protein from the basal diet was about 90% of the recommended allowance and the utilization of urea nitrogen was poor. In the second experiment, with four cows, the intake of digestible crude protein with the basal diet was about 40% of the recommended allowance and the utilization of the nitrogen of urea and of additional groundnut meal was almost complete.

Owing to the way in which the experiments developed the addition of alcohol to the mixture of molasses and urea could not be expected in the present work to increase the utilization of the nitrogen of urea even if it does have that effect under other circumstances. When added to the basal diet very low in nitrogen, the nitrogen of both urea and groundnut meal was used mainly to prevent the withdrawal of nitrogen from body reserves, but partly for a small increase in milk yield.

Under the special conditions of this experiment, which were very favourable for the utilization of non-protein nitrogen, the allowances of digestible crude protein recommended by Woodman (1957) for maintenance of cows weighing 1250 lb (0·73 lb) and 1340 lb (0·82 lb) and giving about 30 lb of milk daily (0·6 lb/10 lb milk) did not appear to be excessive.

In the later stages of the reaction between rennin and casein drastic viscometric methods are undesirable, but in the first stages there is a fall in viscosity which may be satisfactorily measured in an Ostwald viscometer. Using fat-free milk, the viscosity at first falls linearly with time. At low rennet concentrations (Ce) this may be said to constitute a zero-order reaction (constant k0). At higher rennet concentrations and after longer times, the reaction passes to first order (constant k1). After very long times it doubtless becomes more complex.

The values of k0 are proportional, over a considerable range, to the milk concentration (Cm), those of k1 being independent of Cm.

For pure rennin k0 and k1 are proportional to Ce, but for commercial rennets they vary as a power (N) of Ce and the value of N appears to measure the rennin purity. The potentialities of the method for assessing rennet activities are also discussed.

If the reduced viscosity (specific viscosity÷Cm) of fat-free milks is plotted against Cm, good straight lines are obtained which may be extrapolated to zero concentration to give a reliable value of intrinsic viscosity. The intrinsic viscosity falls progressively during the protein breakdown process but the slope of the curves (‘second order term’) remains unchanged.

Treatment of milk with 0·05% (w/v) H2O2 for 8 h at 24°C had no significant effect on the concentrations of seven of the B-complex vitamins or of the fatsoluble vitamins A and E or of carotene. Rat tests showed that the nutritive value of the milk proteins was slightly reduced. This finding was confirmed by microbiological tests with Streptococcus zymogenes, which also showed that the loss was probably connected with that of methionine. The concentration of H2O2 used was effective in controlling bacterial growth during the incubation period, even in a sample of milk with a high initial bacterial count.

Coagulase-negative micrococci isolated from the cow's udder, when cultivated together with cheese and yogurt starters in milk containing 0·3 I.U./ml of penicillin, contributed sufficient penicillinase to permit normal rates of acid production by the starters. Subcultures of such ‘mixed’ cultures also grew at normal rates in milk contaminated with penicillin at the same level.

The possibility of using such micrococci to protect the starter organisms in both the preparation of bulk starters and during manufacture of cheese and yogurt is discussed.