In previous papers by the authors(l,2) it was shown that the vitamin A content of the colostrum of cows varied within wide limits and that the wide range was not due to any differences in dietary, breed or date of calving in animals kept under the same conditions of management. It was also established that calves born of cows whose colostrum possessed a vitamin A content of less than 250 blue units (Moore's) per 100 ml. were more liable to infections such as white scour, navel-ill and joint-ill than were calves from cows whose colostrum had a vitamin A content of more than 250 blue units per 100 ml.

1. A bacteriological study was made of the commercial operation over a period of 4½ years of two Kestner evaporating and spray-drying plants, handling a fairly good and a very poor milk supply respectively. Processes investigated comprised handling of raw milk, pasteurization, climbing film evaporation, handling of evaporated milk, and spray drying. Data were also obtained showing the influence of variations during processing on the moisture content and solubility of powders. Separated milk, full-cream milk, and whey were handled.

2. The general bacterial flora of spray-dried powders and the influence of individual manufacturing processes, packing and storage were studied and possible control methods suggested. Data showing the extent of both hourly and seasonal variations were also obtained.

3. A method of bacteriological analysis is described which gave reasonably good agreement between different workers.

4. Examination of 671 powder samples showed a wide variation in individual plate counts from 200 to 19,500,000 per g. The flora on standard milk agar at 37° C. was of a specialized type and comprised comparatively few species. Thermoduric streptococci of the ‘enterococcus’ and ‘viridans’ groups predominated, Str. durans and Str. thermophilus being the commonest species; in addition, five species of micrococci, probably non-thermoduric, also occurred commonly. Aerobic spore-forming bacilli and three Achromobacter species were found regularly, but their numbers were not of practical importance. Spore-forming anaerobic bacilli were present in 14% of powder samples, probably in very small numbers, and were most frequent during the winter months.

5. Coliform organisms were rarely found in 1 ml. of reconstituted milk, but were isolated from 25% of powder samples when 20 ml. of reconstituted milk was examined; coliforms occurred most frequently during the winter months. False positives due to anaerobes were common, especially in stored powders, and confirmatory tests of presumptive positives were essential. Examination of 198 coliform strains from powders and 164 strains from raw milk showed that coli types occurred less frequently in the powders, whilst aerogenes-cloacae types, particularly cloacae, were more frequent. 48·5% of the powder strains were heat resistant, as compared with 2·2% of the raw-milk strains. It was shown that the coliform flora of powder was partly due to plant contamination by heat-resistant strains, although some non-heat-resistant strains could survive spray drying. It seemed possible that coli types were less resistant to drying than aerogenes-cloacae.

1. Estimations of solids-not-fat by evaporation and by hydrometry were made in two laboratories on samples of the same raw and pasteurized milks.

2. General agreement was found between the results by stated evaporation techniques and those by Richmond's formula (S.N.F. = 0·25G + 0·2F + 0·14) when the latter was applied to milks which had been stored cold (i.e. Recknagel contraction complete as required by Richmond).

3. General agreement at a lower level of S.N.F. (0·2% approx.) was found between Richmond's formula and the density formula (S.N.F. = 0·25D + 0·21F + 0·66) when both were applied to milks heated as required by B.S.S. no. 734 (1937) (i.e. Recknagel effect absent).

4. Adoption of the B.S.S. technique and formula placed a very much greater proportion of samples, below the presumptive legal standard of 8·5% S.N.F.

5. The need is indicated for the standardization of evaporation technique before attempting a permanent revision of the density formula.

6. Seasonal variations between ‘calculated’ and ‘found’ results have been observed.

That bacteriophage is the cause of much loss to the cheese-making industry of New Zealand has been shown by Whitehead(1). In New Zealand in recent years, cheese has been made almost entirely from flash-pasteurized milk with the aid of starters prepared from single-strain cultures of lactic acid streptococci (Str. cremoris). The use of such starters has been accompanied by the occasional failure of the bulk starter to clot, or, if clotted, by failure to produce the required amount of acid in the cheese vat—the latter condition being described by Whitehead as ‘pack up’. Whitehead has traced the cause of sudden failure to air-borne infection of the bulk starter by specific bacteriophage (2), the most probable source of infection being the spray from whey separators. When adequate protection from phage contamination was provided slowness in cheese making disappeared.

1. Following the experiences gained from an earlier experiment, cheese were made at varying controlled pitching points and rates of scald, the experiment being done both with sweet milk and comparatively acid milk.

2. One of the two cheese made from each vat was submitted to physical tests at regular intervals during the ripening process and the other cheese, when ripe, were judged by a panel of experts who also, together with non-experts and routine analysts, gave judgements of firmness and ‘spring’.

3. Tables were drawn up in which the rank orders of the cheese for each objective physical test and subjective judgement are compared with one another.

4. With the possible exception of vapour pressure and ‘spring’, the effect of pitching consistency was much more marked than that of the differences in rate of scald although the latter were considerable. Many physical properties were well correlated with pitching consistency.

5. The cheese makers are shown to have a greater self-consistency as individuals in picking out replicates and as a group in their decisions as to the rank order, by comparison with the other categories.

A method is described for the measurement of the firmness of the rennet curd from 100 ml. samples of milk coagulated under conditions simulating those of the cheesemaking process. Tests with a series of homogeneous curds ranging in firmness from very soft to very hard showed that the curds behaved as elastic gels of varying modulus, and the deformation produced under a suitable compressive load was accordingly adopted as a simple objective measure of firmness.

The method was used to observe the variation in the curd firmness of samples of milk from individual cows and separate quarters, with some observations on the relationship between curd firmness and milk composition, and the effect on curd firmness of variations in the following factors: acidity, addition of calcium chloride, amount of rennet, time of coagulation, and the admixture of soft-curd milk.

The results of these experiments indicate that the method provides a satisfactory measure of the rennet curd firmness of small samples of milk. The utility and applications of the method are discussed, and the suggestion is made that a standardized reproducible test on the same principle should be evolved to serve the same function with regard to milk for cheese making as the standardized measurement of curd tension serves with regard to the digestibility and suitability of milk for infant feeding.