By the application of different water-soluble organic compounds and some protein-denaturing reagents dissolved therein, several stages in the dispersion of milk powder particles can be distinguished. The particles first swell, and agglomeration or coalescence follows. However, no dispersion necessarily takes place at this stage, as indicated by the absence of casein micelles in the surrounding liquid. In the initial stage of self-dispersion, ‘dispersion streams’ emanating from the powder particles may be observed. In certain cases, particularly with spray dried skim-milk, thin membranes may be perceived around the swollen and dispersing powder particles. The dispersibility is dependent upon the fat content of the powder and the method of manufacture.

With propylene glycol and butylene glycol no dispersion of powder particles took place. However, the hydrogen-bond breaking reagents, urea, guanidine hydrochloride and sodium salicylate, as well as an anionic detergent, sodium dodecyl sulphate dissolved in propylene glycol, caused dispersion of powder particles, particularly in spray dried powders. The limited dispersibility of roller dried powders in water could be greatly enhanced by the same reagents.

With water-insoluble liquids enough moisture penetrated through the medium to cause the crystallization of lactose in powder particles.

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.

Whole and skimmed milk spray dried powders have been gas packed by two methods, and the chemical and physical changes taking place during storage at 17 and 37 °C for two years have been measured. The conventional method of double gas packing with nitrogen, with an interval of several days for desorption, was used as a control for a new method employing a single gas packing with a mixture of nitrogen (90%) and hydrogen (10%) plus the inclusion within the can of a solid catalyst pellet containing palladium.

The new system was more effective in removing oxygen and in maintaining an almost oxygen free atmosphere within the cans. Used on a commercial scale it would have several important advantages over the conventional method, and both whole and skimmed milk powders packed in this way would probably be usable after storage for 10 years at normal temperatures.

Because of the low general level of oxygen in all the cans packed by both methods and because of the low moisture content there was little difference in the keeping quality of the powders. What little there was, however, was in favour of the new method.

Since grassland conservation crops are normally bulky fibrous feeds and often limit the appetite and nutrient intake of dairy cows, a feeding trial was made in which a basal ration of hay and grass silage was compared with similar rations containing roots. Three rations were compared in a 12–week winter feeding trial using twelve Ayrshire cows. Ration A consisted of 8 lb of hay and 65 lb of grass silage daily, whilst rations B and C contained 30 and 60 lb of fodder-beet, respectively, in addition. With all three rations concentrates were given at 3½ lb per 10 lb of milk. The total weights of dry matter consumed per day were 29·1, 32·5 and 35·4 lb, respectively, for rations A, B and C and were significantly different. For every 1 lb of additional fodder-beet dry matter eaten the decline in the amount of basal feeds consumed was 0·45 lb. The largest effect was on the silage which fell from 10·8 lb of silage dry matter per day for ration A to 8·8 lb for ration B and 6·8 lb for ration C.

The weight of starch equivalent (S.E.) given per day increased significantly from 18·1 lb for treatment A to 22·2 lb for treatment C, whilst at the same time the total weight of crude fibre and lignin eaten decreased significantly in the rations containing fodder-beet.

The mean daily milk yields for rations A, B and C were 37·4, 39·2 and 38·5 lb, respectively, with a response of 0·9 lb milk per 1 lb of extra S.E. given between rations A and B but no further response between rations B and C. The fat percentages of the milk were not significantly different for the three rations whereas the solidsnot-fat (S.N.F.) varied significantly from 8·58% for ration A to 8·77% for ration C— a response of 0·05% S.N.F. for each additional 1 lb of S.E. The change in the S.N.F. was mainly in the protein fraction of the milk. The cows were significantly heavier when on ration C than when on ration A.

The effect of feeding roots on the appetite of the cow and on the resulting milk quality, and the problems of growing roots on intensively managed grassland farms are briefly discussed.

The presence of pyridoxamine phosphate in extracts of freeze-dried raw and evaporated milks has been demonstrated by separation and identification of the vitamin B6 active compounds by chromatography and electrophoresis on paper. Its presence in the milk extracts is the cause of the higher values for vitamin B6 activity measured with Streptococcus faecalis as compared with those obtained with Str. faecium or Saccharomyces carlsbergensis. This is because Str. faecalis can utilize the phosphate for growth as readily as free pyridoxamine, whereas Str. faecium and S. carlsbergensis cannot. The mild acid treatment used for extracting the vitamin B6 active compounds from the milk samples for microbiological assay was found to be insufficient to hydrolyse the pyridoxamine phosphate. Further treatment of the acid extracts with intestinal phosphatase released the pyridoxamine from its phosphate and increased the vitamin B6 activity measured with S. carlsbergensis and Str.faecium so that the total vitamin B6 activities of the freeze-dried raw and evaporated milks measured microbiologiclly, were then in agreement with the values found in previous tests with chicks and rats.

Pyridoxamine phosphate could only be detected in small amounts in a sample of fresh milk. The possibility that more of it was formed during the processing and storage of the freeze-dried samples is discussed.

In experiments to determine the effect of feeding changes on milk yield and composition, udder disease or injury may easily invalidate the results, particularly those for milk composition. It is suggested that regular examination of the milk from each quarter of the udder would allow a diseased or injured quarter to be recognized and a true value for the effect of the feeding treatment to be obtained from the composition of the milk from at least two healthy quarters. Examples to illustrate the suggestion are given.

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.

Interesterification of milk fats resulted in increased softening points, hardness and high melting glycerides (HMG). Increasing the content of trans-unsaturated acyl groups in milk fat resulted in increased softening points and hardness. While the increased solid fat content after interesterification occurred mostly at the higher measuring temperatures, the increase due to isomerization occurred mainly at the lower measuring temperatures. However, in both cases hardness was increased at all measuring temperatures. These results indicate that glyceride structure and trans-unsaturated acyl content influence the physical properties of the solidified fat.

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.