Two Cheddar cheeses were analysed for aldehydes and methyl ketones at intervals during the ripening period. One-day-old cheese was found to contain acetaldehyde and acetone, together with traces of butan-2-one and pentan-2-one. As the cheese matured heptan-2-one, nonan-2-one and undecan-2-one appeared, and the concentrations of all these compounds progressively increased.

One half-udder from a lactating cow was perfused for 110 min with blood containing 1 mc of [1-14C]butyrate. Inactive sodium butyrate was added at the eightieth minute. The volume of milk collected was 320 ml. One half-udder from another cow was perfused for 120 min in the presence of 0·5 mc [3-14C]butyrate, inactive sodium acetate being added at the sixtieth minute. The volume of milk collected was 150 ml.

The total amount of 14CO2 recovered was 5·7% of the [1-14C]butyrate given and 7·6% of the [3-14C]butyrate given. In both instances casein, followed by the volatile fatty acids, showed the highest specific activity of the constituents isolated from the milk. The glyceride fatty acids in the udder were fifty times as active as those in the milk. With [3-14C]butyrate the activity of the total fatty acids amounted to 24% and that of total lactose to 0·38% of the added 14C. Butyrate did not appear to be used for glycogenesis in the perfused gland. The specific activity of the lower fatty acids of both the udder and the milk increased stepwise with increasing chain length to reach a maximum at C10. A satisfactory explanation for this peculiar 14C distribution cannot be given at the present time. There was no evidence of direct esterification of butyrate. Most of the activity of casein was due to labelled glutamic and aspartic acids, the activity of the former being four times as high as that of the latter. The acids of the Krebs cycle isolated from the udder tissue when [3-14C]butyrate was given showed very high activity. No striking differences were observed between the results of the two experiments. It is concluded that butyrate is split into two C2 components which behave identically. These are utilized for fatty acid synthesis and take part in the Krebs cycle. The relative 14C distribution between the components isolated from milk and those from tissue may be a reflexion of the secretory processes in the udder cells, synthesized fat tending to be secreted in the alveoli after the other constituents.

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.

The distribution and development of bacteria during the maturing of New Zealand Cheddar cheese have been studied using stained sections of cheese. The starter streptococci usually occur singly and in small groups throughout the mass of the cheese, their distribution on a microscopic scale being very irregular. In contrast, the bacteria developing later form discrete microcolonies, most of which are associated with the curd junctions. Instead of adding lactobacilli to milk, smaller numbers may be added to the dry curd before cheddaring or after milling. Some observations on the physical structure of cheese are made.

The ratio of phage-resistant to phage-susceptible chains in five strains of Streptococcus cremoris and two of Str. lactis was investigated. It was shown that this ratio varied between strains and was decreased when the cultures were subcultured with extremely small inocula ( <50 chains/ml) and increased with relatively large inocula (1%). It is suggested that resistant cells arise by mutations occurring in the absence of phage.

Observations were made by anoptral phase-contrast microscopy of the effect of various reagents on the state of dispersion of casein micelles in skim-milk and in lactic acid and rennet coagula. Among the hydrogen-bond-breaking reagents, urea at higher (4M) concentration dispersed the casein micelles in skim-milk and in acid and rennet coagula. Sodium salicylate was effective at low (M) concentration. Guanidine hydrochloride at low concentration caused aggregation of the micelles in skim-milk but at high concentration caused dispersion, while at both concentrations it dispersed acid and rennet coagula. Lithium iodide and potassium thiocyanate flocculated the casein in skim-milk, but dispersed it in both types of coagula. Flocculation in skim-milk by these reagents was followed by slow coalescence of the casein.

At substantially lower molar concentrations, sodium dodecyl sulphate, an anionic detergent, which attacks either the hydrophobic bonds or the salt linkages in proteins, dispersed micelles and both types of coagula. Sodium thioglycollate, a disulphide-bond-breaking reagent, had no visible effect on the casein.

In rennet coagulum in which the calcium bridges have been destroyed by the sequestering action of EDTA or in lactic acid coagulum, urea at low concentrations caused a quick and almost complete coalescence of casein. Fibres were formed in the rennet coagulum when the coalesced material, which presumably consists of randomly coiled chains of unfolded casein macromolecules, was subjected to stretching or flowing. Similar chemical and physical conditions would appear to prevail when fibre formation takes place in cheddaring cheese curd.

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 use of starter cultures prepared 3 days, 2 days and 1 day before inoculation at the 1% level into cold cream in the making of sweet cream starter butter was investigated. With Streptococcus diacetilactis starter there was little effect of age of starter on diacetyl production in the cream and on the quality of the fresh butter, but when 3-day-old culture was used in the cream there was a slight reduction in the butter quality after 4 and 8 months' storage. With the mixed commercial cultures Camb and F.D. increase in age of the culture led to reductions in diacetyl production in the cream. The difference was attributed to the effect of holding for the longer time under acid conditions on the equilibrium between streptococci and leuconostocs in the mixed culture. The age of the Camb culture had no effect on the grade of the butter, but holding the F.D. culture for 3 and 2 days instead of for 1 day caused a fall in grade of the butter after storage for 4 and 8 months at 14 °F.

A description is given of various methods for the ultrafiltration and dialysis of milk and of the composition of the sera obtained. Ultrafiltrate prepared by the procedure recommended is reasonably representative of the aqueous phase of milk, but its content of lactose and citric acid, and consequently also of calcium, is determined to a slight degree by the sieving phenomenon known to occur often in ultrafiltration. The composition of diffusate obtained from milk at 20°C is not thought to be controlled to any significant extent by a Donnan effect and is regarded as identical with that of the aqueous phase of milk. The lactose content of diffusate suggests that about 2% of the water in milk is bound to protein, and allowance should be made for this when calculating the concentrations of the soluble constituents in milk from the composition of diffusate. Diffusate prepared from milk at 3°C contains slightly more total calcium, ionized calcium and phosphorus than diffusate prepared at 20°C. These differences are attributed to a change in the partition of calcium and phosphorus between the disperse and aqueous phases at the lower temperature, an explanation that is supported by the reversibility of the change. The composition of diffusate prepared by the procedure recommended indicates that about 5% of the sodium and about 6% of the potassium and citric acid in milk are in the disperse phase.

Rates of flow of milk during milking have been observed on twin and single-born dairy cows with the aid of a device for continuous recording of weight of milk extracted. Each cow has been characterized by a maximum rate arrived at by averaging morning and evening observations on 2 days. Only this maximum rate has been studied.

Repeatability was high (0·8–0·9) whether measured from day to day or from lactation to lactation. Maximum rate of flow was 10–16% higher in second than in first lactations. The range extended from under 2 lb/min to over 7 lb/min.

Lactation yield of milk varied significantly with rate, rising about 50 gal for an increase of 1 lb/min. This relation is reduced or eliminated by taking into account by partial regression analysis either maximum weekly yield or the increase from the second to the peak week of lactation.

Although the higher yielding cows had larger udder areas bounded by the four teats, the regression of 305-day milk yield on rate was not changed much by taking udder area into account. Cows with short teats milked faster and had higher yields than cows with longer teats.

Differences in yield among the four quarters widened slightly between 1 and 3 months of lactation regardless of rate of flow, except possibly in the three slowest milking cows. In these the differences increased three times as much as in the other cows. The wider the inter-quarter differences in yield the less the proportion of milk obtained at the maximum rate.

Heritability of maximum rate of flow derived from observations on paired singleborn cattle and twins was 85%. Field data would probably yield a value of 60–70%. Appropriate selection of breeding stock would effectively alter rate of flow, but there is no reason yet to expect yield of milk to change except perhaps by reducing the incidence of very slow milking cows.

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.

Two experiments were carried out, Expt. 1 with twelve cows in a 4×4 Latin square and Expt. 2 with twenty-six cows in two groups which spent 11 weeks on the experimental rations. In both experiments hay and silage were fed ad lib. In Expt. 1 four levels of concentrate feeding were offered, 1¼, 2½, 3¾ and 5 lb/gal, and in Expt. 2 two levels, 1¼and 5 lb/gal. The levels of feeding as a percentage of Woodman's standards for starch equivalent (S.E.) ranged from 82 to 125% in Expt. 1 and from 83 to 116% in Expt. 2; for digestible crude protein (D.C.P.) the corresponding figures were 70–100% and 105–107%. When concentrate consumption increased by 1 lb dry matter the consumption of bulk feeds was reduced by 0·18–0·22 lb dry matter but the total fibre intake remained constant. Milk yield showed small but significant responses to level of feeding. Average responses per 1 lb S.E. were 0·77 lb milk in Expt. 1 and 0·61 lb milk in Expt. 2. Total lactation yields of the cows in Expt. 2 were unaffected by the experimental treatments. The production S.E. fed per gallon of milk ranged from 1·71 to 3·72 lb in Expt. 1 and from 1·92 to 3·27 lb in Expt 2. Production D.C.P. ranged from 0·37 to 0·63 lb and from 0·67 to 0·70 lb, respectively.

High levels of feeding increased the S.N.F. and protein contents of the milk but did not affect other constituents. The responses in S.N.F. were lower than in some other experiments and some cows showed no response. The results are discussed with reference to the experimental methods and also with reference to the yield responses compared with published data, and to the practical importance of the high production obtained with low usage of concentrate feeds.

When washed cream was treated with copper and ascorbic acid and held at 2°C for 1–5 days a strong metallic, fish-oil flavour developed. Compounds responsible for the flavour were isolated and identified. Gas chromatographic separation of a flavour concentrate on a silicone oil column gave six characteristic flavour fractions which, in order of elution, were described as painty or drying oil, oily, mushroom, metallic, tallowy and cucumber. The flavours of all fractions were predominantly caused by carbonyl compounds and the oily and metallic fractions were the main contributors to the typical fish-oil flavour. The following compounds were characterized: n-pentanal and pent-2-enal in the painty fraction; n-hexanal, n-heptanal and hex-2-enal in the oily fraction; hept-2-enal and a carbonyl compound with a mushroom odour in the mushroom fraction; a carbonyl compound with a metallic odour in the metallic fraction; n-octanal, n-nonanal, oct-2-enal and hepta-2,4-dienal in the tallowy fraction; and non-2-enal in the cucumber fraction.

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.

A distinct fish-oil or cod-liver-oil flavour appeared after storage in commercial butterfat containing, as an antioxidant, nordihydroguaiaretic acid (NDGA) and citric acid dissolved in propylene glycol. The fishy condition was reproducible in the laboratory by the combined effect of NDGA with either citric or lactic acids. The acids alone in butterfat gave oily and rather less clearly defined fishy flavours after storage.

From butterfat with tallowy and painty flavours, the same range of carbonyl compounds was obtained as from fishy flavoured butterfat or washed cream. They consisted of the C5–10 n-alkanals, the C5–10 alk-2-enals, hepta-2, 4-dienal and a compound with a metallic flavour. Heptan-2-one, present only in small amounts in washed cream, was also isolated. Three factors distinguished the tallowy and painty from the fish-oil flavoured butterfat. There was a relative increase in n-heptanal, n-octanal, n-nonanal, heptan-2-one, hept-2-enal and non-2-enal in the tallowy butterfat and a relative increase in n-pentanal and the C5–10 alk-2-enals in the painty butterfat. Secondly, the ‘metallic’ compound was present in such small relative amounts in both the tallowy and painty flavoured butterfats as to have no effect on the flavour. Thirdly, the total weight of volatile carbonyl compounds was about 10 times greater in the tallowy and 100 times greater in the painty butterfat than in the fish-oil flavoured butterfat.

A study was made of the effect of various sampling intervals on the accuracy of estimating lactation milk yield, fat yield, solids-not-fat (S.N.F) yield, fat percentage and S.N.F. percentage. The basic data consisited of daily milk, fat and S.N.F. yields for eighteen lactations made by twelve Dairy Shorthorn cows. Estimates of the lactation yields and quality were obtained using sampling intervals of 7, 14, 28, 42, 56 and 63 days, and were expressed as differences from the actual values. Only in the case of milk yield was there any effective bias in the estimates. This bias increased with increasing sampling interval.

The distributions of differences between estimated and actual values are presented. The error of estimation increased with increasing sampling interval. Keeping in mind the comparatively small-sized sample used in the investigation, the results are discussed in the light of the purposes for which records are kept.

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.