The investigation of the non-starter bacterial flora of Cheddar cheese during the first few weeks of the ripening period is rendered difficult by the great preponderance of starter streptococci in the bacterial population. It was found that the starter streptococci could be eliminated from agar plates containing various dilutions of the emulsified cheese by the use of phage specific for the pure culture starters used to make the cheese or alternatively by the use of α-bromopropionic acid.

The successful use of the phage method of eliminating lactic streptococci from bacterial mixtures in poured agar plates depends on the use of single strain starters, and on the absence of phage-resistant forms in the culture used. The latter objective may be achieved by use of starter strains showing a low proportion of resistant cells in a normal culture and by taking precautions to avoid excessive phage development during the cheesemaking process.

A new method for determining the composition of the colloidal phosphate of milk has been developed, based on analysis of milk free from colloidal phosphate. Preparation of this material is described.

The results suggest that the so-called colloidal calcium phosphate of milk should be more properly described as a colloidal phosphate—citrate.

This colloidal phosphate—citrate shows considerable analytical resemblance to the precipitate formed on neutralizing acidified milk serum. Both can be represented approximately by the empirical formula of a hypothetical citrate apatite.

Ten farms in the county of Durham took part in a field study of the effects of feeding and of udder disease on the level of non-fatty solids (s.n.f.) in milk. Statistical analysis of the resulting data showed that age, pregnancy, season of the year, and total cell count affected the percentage of s.n.f. and that these effects were additive and independent of each other. No effect associated with nutritional changes could be demonstrated.

The principal effects of the factors, each one freed from effects of other factors, were as follows:

Herds in which s.n.f. had been consistently low over a period of years were compared with herds in which s.n.f. had been satisfactory. Analysis of the data showed that about 70% of the difference in s.n.f. between these groups could be accounted for by differences in age of cow, stage of lactation, cell count and breed.

There was some evidence of a residual effect following clinical mastitis that could not be accounted for by residual high cell counts.

The within-cow regression of s.n.f. on log cell count calculated from the Durham data and from van Rensburg's data was on both occasions negative.

The implications of these findings are discussed, particularly in relation to advisory work.

The technique of paper chromatography of bacterial extracts has been successfully applied to the routine examination of lactobacilli from cheese. One hundred and nine strains isolated on selective media have been grouped by their chromatogram patterns, and selected strains from these groups have been shown to have biochemical characteristics giving relationships which are in agreement with the chromatogram groupings. The results indicate that the technique can be used routinely for the rapid identification of strains of lactobacilli.

Seven strains of Streptococcus cremoris, four strains of Str. lactis, and one strain of Str. diacetilactis were examined for their ability to produce aldehydes and methyl ketones when grown in skim-milk. All strains were found to produce acetaldehyde and seven also produced acetone. No other aldehydes or methyl ketones were detected in any of the cultures.

A method for the quantitative estimation of mixtures of aldehydes and methyl ketones by means of paper chromatography of their 2,4-dinitrophenylhydrazones is described.

The diet and milk from a herd of dairy cows were analysed regularly for 90Sr and calcium. The ‘observed ratio’ (the ratio of 90Sr to calcium in the milk divided by the ratio of 90Sr to calcium in the diet) was found to be 0·10 against 90Sr in favour of calcium, which corresponds well with the results of other workers. The amount of 90Sr secreted into the milk was 1·2% of the total ingested. Similar values were obtained using stable strontium data.

Soil samples from different depths and herbage were taken from three areas with different cultivation histories and analysed for 90Sr and calcium. The effect of ploughing on the vertical distribution of 90Sr in soil and on the 90Sr levels in vegetation was examined.

Dried skim-milk stored at 55°C in air at 70% relative humidity has been found to contain lactulose, galactose, tagatose, glyceraldehyde and maltol; and formic, acetic and glycollic acids. These compounds are not present, or are present only in trace quantities, in fresh dried skim-milk. It is suggested that while the proteinsugar reaction is responsible for most of the browning of the powder, many of the compounds found are formed by degradation of lactose catalysed by the free basic amino groups of the casein. The compounds so formed probably then react with amino groups in a Maillard reaction and thus contribute to the browning of the milk powder.

A detailed study has been made of spectroturbimetric methods for testing the degree of homogenization of milk, and it has been shown that, provided care is exercised in the design of the turbimeter, the turbidity index at a specified wavelength provides a useful practical measure of the degree of homogenization. This measurement can easily be made with a simple filter turbimeter.

The effect of ultra-high-temperature (U.H.T.) sterilization and of subsequent in-bottle sterilization on the availability of milk calcium has been studied in experiments with rats. The heated milks and the raw milk from which they were prepared were freeze-dried and added to a diet low in Ca so that the resulting diets contained some 0·11% Ca and 0·42% P.

Ca retention by groups of six litter-mate male weanling rats was 98·4, 98·4 and 98·5% respectively from diets containing raw milk, U.H.T.-treated milk and milk treated by U.H.T. followed by in-bottle sterilization. It is clear that these processes did not affect the availability of milk Ca.

Batches of cream inoculated with 1% of a culture of Streptococcus diacetilactis or of one or other of two mixed starters were held at different temperatures over the range 37–57°F before churning. Diacetyl and acetoin were estimated in the creams at churning and in the butters fresh and after storage.

The diacetyl production of all three starters in the cream increased with increase in temperature, although at the lower temperatures there was no indication of any rise in titratable acidity. At 52 and 57°F there was some rise in acidity during the holding period.

The butters were of good keeping quality. There was a small but definite reduction in the diacetyl content of the butters during storage, but the extent of the change was not related to the holding temperature of the creams.

It was concluded that if sweet cream starter butter is to be made with uniform intensity of flavour the proportion of starter added must be adjusted to counterbalance changes in the cream-holding temperature.

Production of diacetyl and acetoin by starters in cold skim-milk and cream was shown to increase with increase in the proportion of starter culture added, with some limitations at the higher rates of starter addition.

With Streptococcus diacetilactis starter in skim-milk at 50°F the relation between proportion of starter added and production of diacetyl was linear up to addition at the 4% level, whereas at 43°F it was approximately linear up to the 10% level. At both 50 and 43°F the relation between the proportion of starter added and the production of acetoin was linear up to the 10% level.

With Camb starter in skim-milk at both 50 and 43°F there were regular increases in production of diacetyl up to the 4% level of addition, but only minor changes thereafter with increase in the proportion of starter added up to 10%. At both temperatures the maximum production of acetoin was reached with the 7% rate of addition.

Production of diacetyl and acetoin in skim-milk was greater at 50°F than at 43°F with both starters for all proportions up to 10%, and it was greater for Str. diacetilactis than for the mixed cultures.

Except at the higher rates of addition of starter and at the higher temperature there were no concomitant increases in the acidity of the milk or lowering of the pH values. It appears that at low temperatures production of diacetyl by starters in sweet milk and cream proceeds independently of production of lactic acid.

Similar results were obtained in a series of experimental buttermaking trials and some small commercial-scale trials, in which varying proportions of starter were added to creams after pasteurizing and before holding overnight for churning. With the cream-holding temperatures used, mainly 40–50°F, the pH values of the butters were not appreciably lowered by the starter additions to the cream. At all the rates of addition there were with Str. diacetilactis starter higher contents of diacetyl in the butter than with Camb starter. There was no indication of any relationship between the proportion of starter added and the keeping quality of the butter.

Results are reported of an experiment with fattening pigs, made under commercial conditions, on the effect of adding formalin to liquid skim-milk, to delay souring, on the nutritive value of the milk given either in restricted or in unrestricted quantities.

There were four treatments: (i) Meal, fed to a scale based on live weight, plus sour skim-milk restricted to a maximum of 5¼ pints per pig per day. (ii) As (i) except that milk kept sweet by the addition of 0·15% formalin shortly after separation, was fed. (iii) Daily allowance of 2 lb meal/pig fed throughout the fattening period plus an unrestricted supply of sour skim-milk. (iv) As (iii) except that milk kept sweet by the addition of 0·15% formalin shortly after separation, was fed.

There were five pens of nine group-fed pigs on each treatment, involving a total of 180 pigs. The pigs were on experiment from about 9 weeks of age to bacon weight. Comprehensive carcass measurements were made on all the pigs, and bacon-tasting tests were made on samples of both green and smoked bacon from a number of the carcasses.

There were no significant differences between any of the four treatments in rate of growth or overall efficiency of food utilization.

Pigs given formalin-treated milk had a significantly thinner layer of back fat over the loin than those given sour milk. Although the difference was relatively small, it was apparent whether the milk was fed in restricted amounts or ad lib. and was reflected in the commercial grading results. There were no significant differences between treatments in dressing percentage, carcass length, shoulder back fat thickness, belly thickness or size of eye muscle.

No taint or off-flavour was detected in samples of green or smoked bacon from pigs fed milk to which 0·15% formalin had been added.

The feeding of liquid skim-milk in unrestricted quantities is discussed in relation to the comparative prices of meal and skim-milk.

The importance of adding the formalin to the skim-milk as soon as possible after separation, particularly during warm weather, is stressed in order that souring might be delayed for at least 1 week.

Data available for fifty cows mainly infected with Staphylococcus pyogenes have been analysed to determine the effects of udder infections and mastitis on milk, fat and solids-not-fat yield and on fat and solids-not-fat percentages over full lactations.

It was found that lactation yields of milk, solids-not-fat and fat were depressed by 10, 11 and 12% respectively in the presence of infection. These depressions were significant (P < 0·05). The composition of the milk averaged over whole lactations was not significantly affected (P > 0·05), although the mean solids-not-fat percentage of the milk was significantly depressed by 0·196±0·092 during the period of infection.

It is suggested that the depressions in lactation yield and changes in milk composition would have been greater in the absence of antibiotic therapy for mastitis.