It has been shown that human milk, like cow's milk, increases in fat content during suckling. The increase is not associated with any systematic change in fat globule size distribution. Human milk fat globules, like those of the cow, have been shown to cluster at body temperature. These facts support the theory that the increase in fat content during suckling is due to the fine ducts filtering out the larger globule clusters.

The considerable increase in efficiency of taint removal which can be attained by counterflow methods is shown by the extension of the algebraic and graphical methods of Part I and confirmed by experiments with the reference substances diacetyl and acetoin in water. The treatment is mainly confined to multiple contact counterflow, and several methods are suggested by which existing Vacreator equipment may be used for counterflow connexion. The effect of a feed temperature below the temperature existing in the contacting vessels is shown to increase the amount of taint removal per pound of stripping steam used. Comparative curves are given for total steam consumption for systems preheating to various temperatures with waste heat.

Results are given for experiments with a converted small size Tandem Vacreator. For diacetyl, the stripping steam used was one-tenth of that for a single contact process over the same range of diacetyl removal. Acetoin, being less volatile than diacetyl, did not show the same large steam saving.

1. The composition has been studied of the milk of forty-four sows in the course of sixty-eight lactations. The milk was obtained by machine milking following intravenous injection of oxytocin.

2. Definite lactational trends have been observed for all the major constituents, and the third week seems a critical stage for most of the milk components.

3. The mean values for the milk, based on the analyses of over 450 samples from the seventh to fifty-sixth day of the lactation were: fat 9·58 %, protein 6·11 %, lactose 4·62 %, ash 0·92%. Such figures are considered to be rather meaningless for most practical purposes, in view of the marked changes over the course of lactation.

4. The day-to-day variation in the composition of sow's milk has been studied. Whereas the fat value changes considerably, the non-fat constituents show a less marked variation. Difficulties in securing a representative sample of the weekly milk have been overcome by preparing a composite sample from three milMngs within the week.

5. Some preliminary work has been done on variation in the composition during the process of milking. Sequential samples show an erratic fat content, especially during the early part of the lactation. When calculated on a fat-free basis, the protein, lactose and ash contents are relatively constant during the process of milking.

An inverse relationship has been demonstrated between the titratable acidity and formol titre of raw separated milk heated at temperatures of 60, 70 and 80° C. suggesting that the combination of lactose and protein, with the elimination of basic amino groups attached to protein, is one of the main reactions responsible for the heat-induced acidity. At temperatures of 90 and 100° C., when thermal decomposition of protein takes place, heat-induced acidity develops very rapidly and is accompanied by a marked increase in the number of basic amino groups and in the number of these groups which combine with lactose. Below 80° C. the development of acidity was not accompanied by discoloration of the millk, but at 80° C. and above, browning of the milk occurred. The relation between heat-induced acidity and browning is discussed.

The loss of moisture per pound of free moisture in a cheese is shown to depend on the moisture movement in the cheese and hence on a function of the group (diffusion rate × time/(height)2). The results of a series of experiments were correlated by means of the above expression. The variables correlated were time of storage, moisture content, fat content, air humidity, air temperature, size and shape of the cheese. Total moisture affects the free moisture value, and air humidity affects the free moisture via the equilibrium moisture. The main effect of temperature is on the rate of moisture diffusion, and the fat content also affects the rate of moisture diffusion. All experimental results for close-bodied cylindrical cheeses were approximately correlated by the expression.

1. The refractive index and density of butterfats were determined for butters forwarded by twenty factories at 8-week intervals over a period of 3 years. The refractive index (n40) ranged from 1·4535 to 1·4571, with mean weighted value of 1·45492. The density (D60) ranged from 0·8885 to 0·8916, with mean weighted value of 0·89045.

2. Minimum refractive index results were found in the summer butterfats and maximum results in the winter butterfats, i.e. at opposite seasons to the occurrence of the minimum and maximum in Northern European butterfats. Maximum density results were found in late spring butterfats and minimum results in autumn butterfats.

3. The mean monthly results for refractive index and for density of North Island and South Island butterfats showed an appreciable divergence only during the winter months.

4. The correlations between refractive index and iodine value, between density and saponification value, and between density and Reichert value, on 140 butterfats sampled over 1 year were all highly significant.

In studies where regular analyses of sow's milk are being made in an effort to evaluate the total energy content of the milk from sows at different dietary levels, once the composition trends of the milk have been assessed, the number of analyses can be considerably reduced and a greater number of samples handled. Satisfactory calorific values can be obtained from the estimated composition requiring analyses for fat and total solids only.

Titration curves of calcium-containing and calcium-free solutions resembling milk serum indicated that precipitation of calcium from such solutions was greatly impeded by citrate. In the absence of citrate, precipitation of tricalcium phosphate was complete at pH 6·0, but, in solutions containing citrate, precipitation of tricalcium phosphate occurred gradually throughout the titration and was not complete at pH 10.

In some solutions precipitation of calcium phosphate ceased at about pH 9·7, even though the base added had been insufficient to neutralize tertiary hydrogen equivalent to the known calcium content. Precipitation of dicalcium phosphate must therefore have occurred.

The observed stability of calcium in these solutions was much greater than that predicted from the accepted solubility and dissociation constants. It is therefore concluded that detailed studies of these constants, and of the factors controlling precipitation of dior tricalcium phosphate, are needed.

1. Measurements of hardness and ‘free-oil’ content of samples of butter from cream held at various temperatures before churning were made before and after storage. Hardness was determined by the sectility method, while free-oil content was estimated from the weight of oil exuding from thin slices of butter sandwiched between filter-papers and held at 64–4° F. (18° C).

2. Butter from cream held at 60° F. and churned at 45° F. was much softer and contained more free oil than butter from cream held and churned at 45° F.

3. If the cream was precooled to 45° F. before being held at 60° F. the butter was very slightly softer than that from cream held at 60° F. without precooling, but the difference disappeared after storage. It contained rather less free oil, but the softening point of the oil was lower. Fat losses in churning which were high where cream was held at 60° F. were reduced almost to normal when cream was precooled before being held at 60° F.

4. Cream slowly cooled to 45° F. yielded butter which was softer and contained more free oil than that from cream cooled rapidly to 45° F. and held at that temperature. The butter, however, was not so soft as that from cream held at 60° F.

5. Butter from cream held at a temperature below that at which it was to be churned did not differ significantly in hardness or free-oil content from that produced from cream held at the churning temperature.

6. Present commercial methods of cream treatment in New Zealand (rapid cooling to churning temperature and holding at that temperature) give butter of almost maximum hardness for the type of fat involved at each stage of the season.

7. More uniform consistency of butter throughout the season could be achieved only by reducing the hardness of the firmer butter and not by increasing the firmness of the ofter butter.

Cream samples (200–500 ml.) are churned in about 1 min. in a covered beaker by an agitator directly coupled to a ¼ h.p. electric motor. The beater sweeps the whole of the enclosed space so as to prevent thickened cream from collecting in places where it can escape agitation.

A high proportion of the group ‘N’ streptococci, isolated from Cheddar cheese curd, produced volatile acids and acetoin, in varying degrees, in milk culture. The active acetoin-producing strains closely resembled type strains of Str. diacetilactis (Matuszew-ski) and Str. citrophilus P.R.M. but differed from them in producing acetoin in lactose broth. The weak acetoin-producing strains resembled Str. cremoris HP in this characteristic, but in their morphological and cultural reactions, mor e closely resembled Str. lactis. The titratable acidity in milk cultures varied inversely with the production of volatile acids and acetoin.

1. The vitamin D potency of three samples of south Indian butter has been determined in prophylactic tests with rats.

2. Two samples of butter from Bangalore contained 0·56 and 0·41 i.u. vitamin D/g. fat, a sample from Coimbatore contained 0·29 i.u./g. fat.

Coat formation in Stilton cheese is started 5–10 days after manufacture by scraping the surface to fill in crevices and to smooth the coat. Normally the cheese, when ready for scraping, is firm at the surface, greasy to the touch and smells like ripe pears. In some dairies, however, an abnormal condition known as “slip-coat” may be apparent at the scraping stage. The cheese is not firm to the exterior, but has a layer of softened material ½–¾ in deep resembling a partially drained cream cheese. The texture is flaky, whereas in the scrapings from the surface of a normal cheese the texture is granular. Patches of grey, or, less commonly, yellow or brown discoloration, may be formed at the surface of slip-coat cheese.

Severe losses are caused in some types of cheese by the growth of spore-forming anaerobes. The species most commonly involved is Clostridium butyricum and its variants, but other clostridia such as Cl. sporogenes (Bacillus putrificus of Dorner (1)) may also be concerned. Existing methods for the study of the properties of these organisms are inadequate, a fact on which Rosenberger(2) has commented. This work has been particularly concerned with devising a medium suitable for all clostridia, which is clear, simple to prepare, and which requires no special anaerobic precautions in its use.

1. Many single-strain lactic streptococci used as cheese starters exhibited a difference in susceptibility to an inhibitory substance present in raw and H.T.S.T. pasteurized milk, some being markedly affected whilst others were completely resistant to this inhibitory aubstance.

2. The inhibitory effect of raw or partially heated milk on ‘susceptible’ strains of starter streptococci appears to be a widespread phenomenon. It can be said that the inhibitory substance is normally present in all milk supplies throughout the year. It occurs in milk freshly drawn from the udder aseptically.

3. Heating the milk to boiling-point for variable periods or autoclaving the milk destroys the inhibitory effect of the milk on ‘susceptible’ cultures.

4. The inhibitory substance is closely associated with the fat globules in milk and can exert a marked effect owing to the large surface area exposed.

5. Growth-stimulating substances prepared from extracts of fowl liver, separator slime, and yeast were able to overcome the inhibitory effect when added to raw milk. However, the effect of these substances were markedly depressed on the addition of small amounts of freshly separated cream to the cultures.

6. It is suggested that the above growth-stimulating substances contain a common growth factor which enters into competition with an inhibitory substance closely associated with the fat globule.

7. The inhibitory substance appears to be bacteriostatic in its effect and not bactericidal.

8. Owing to the heat lability of the inhibitory substance and its presence in close association with the fat globule, it is suggested that it may be enzymic in nature.