Determinations of hardness were made on 324 samples of butter drawn monthly for 3 years from nine factories distributed throughout New Zealand. The results were compared by statistical methods with the iodine values and softening points of the corresponding butterfats which had been determined by Cox & McDowall(4). It was shown that the softness (reciprocal of hardness) was significantly correlated with both iodine value and softening point, which together explained 55 % of the variation in softness observed. Of the remaining variation, 59% was due to seasonal changes other than those in iodine value and softening point and 36 % to differences between factories. It is considered that manufacturing variations were responsible for very little of the seasonal variations, and that the differences between factories were due as much to district differences as to manufacturing differences. It is concluded that only a small part of the variation in softness of the butter samples was due to manufacturing variations, and that at least 80 % of the variation could be attributed to differences in the raw material.

1. The Lovibond Tintometer has been found more reliable than either the Pulfrich Photometer or the Spekker Absorptiometer for the assessment of the blue colour from the Carr-Price test on butterfat unsaponifiable residues.

2. Using a Beckman Spectrophotometer, vitamin A in butterfat unsaponifiable residues has been estimated also by the intensity of absorption at 325 mµ. From spectrophotometric readings at this wavelength and at 450 mµ, the irrelevant absorption, due both to carotenoid and non-carotenoid compounds, may be calculated as follows:

Corrected density reading at 325 mµ = 9/10 (A – 12/100B),

where A = density reading of the unsaponifiable residue in petrol ether at 325 mµ, B = density reading of the same solution at 450 mµ.

3. The Morton & Stubbs equation for irrelevant absorption in fish-liver oils is not generally applicable to butterfat unsaponifiable residues.

4. A comparison of the vitamin A content of butterfat samples by the Carr-Price test and by the direct spectrophotometric method has shown a reasonably good agreement between the two values.

The milk of 100 cows and of the same number of buffaloes, in Cairo and its neighbourhood, was analysed; analyses were also made on bulk samples taken at 2-week intervals from the milk of the two buffalo and cow herds of the Faculty of Agriculture at Giza. All samples were mixtures of morning and evening milkings in proportion to yield.

The Bird & Derby method of calculating percentage butterfat loss in buttermilk is in error because it assumes that all the buttermilk in the granules at draining is retained in the buttermilk, whereas much of it is washed out in the wash water. Lactose estimations in butter and buttermilk confirm Udy's finding that butter contains about 10% of buttermilk. The Udy formula, viz.

is therefore in this respect correctly based and can be applied to individual churnings of butter in the same way as the Bird & Derby formula has been applied. The Bird & Derby formula should be discarded except for use when the granules are not washed with chill-water.

Both the Udy and the Bird & Derby formulae do not allow for the content of fat in the buttermilk retained in the butter or for the influence of fat content of the buttermilk on the calculated quantity of serum lost. When these factors are taken into account the Udy formula becomes

The correction +0·0012f F is not significant.

Of the four main factors commonly regarded as influencing keeping properties of ghee, viz. moisture content, acidity, heat treatment and type of bacterial culture used in souring, the heat treatment was found to be the most important.

In general, the higher the final temperature (110° C. and higher) attained during evaporation, the better were the keeping properties of the product, providing that the butter had been heated in contact with curd, boiled as rapidly as possible, and given a minimum amount of stirring.

The improved keeping properties conferred on ghee heated to 110–150° C. were promoted by antioxidants (apparently phospholipids) extracted from the curd during cooking.

Initial acidity and moisture contents had no effect on storage life of ghee at 38° C., and the practice of grading ghee according to its acidity would appear to be of questionable value. Souring of milk to give 2·5–3·0% lactic acid and the accompanying desirable flavour did not detract from the keeping quality of the ghee made from it.

The type of bacterial culture used for souring had only slight influence on keeping quality of ghee, but a marked influence on flavour.

Storage life of ghee at 38° C. (‘Indian summer temperature’) could be predicted with fair accuracy from its rate of oxidation at 100° C. in a ‘Swift oxidation tester’.

Penicillin present in cheese milk affected the performance of various ‘single strain’ starter cultures in the cheese vat.

A concentration of 0·07 penicillin unit/ml, in the milk was sufficient to cause a complete failure or ‘dead’ vat with the most sensitive strain of Str. cremoris. Two strains ceased to produce acid in the later stages of the manufacturing process when the milk contained 0·10 unit/ml. With three other strains the 0·10 unit/ml, level delayed acid development; the experimental vats required 20–40 min. longer than the controls to reach ‘salting’ acidity.

Flash pasteurization temperatures usually employed in cheese-making (150–160° F.) did not appreciably alter the activity of penicillin in the cheese milk.

The quality of the cheese produced was influenced by the rate and extent of acid production by the starter cultures in the vat during manufacture.

Experience in the field indicates that where a large number of cows are treated simultaneously for mastitis, there may be sufficient penicillin in the cheese milk to affect the starter, if the milk from quarters undergoing treatment is included in the bulk milk.

An experiment is described in which ratings on some 200 cheese made on 31 different days were rated for firmness, quality, springiness and crumbliness, both when 2 weeks and 8 weeks old. Some of the relationships between the ratings are discussed, in particular the ratings for firmness and quality. By means of the firmness ratings made on the cheese at 2 weeks, twenty-eight cheese out of 211 could have been screened off, and of these twenty-eight, nine were subsequently seriously down-graded for quality. Only two cheese which were not screened off developed unsatisfactorily to the same degree. Individual differences between judges are noted, especially with regard to quality. The cheese-maker considers the cheese to be about 1 point higher in quality (on a 7-point scale) than the remaining judges. One judge who criticizes adversely about three times as many cheese as the remainder of the judges also down-grades about six batches of cheese which are not down-graded by the remaining judges.

Cultures of lactic streptococci partially resistant against a phage race and growing in regular association with that race are, as a result of the presence of the phage, protected from attack by some other races of phage. Such phage-carrying cultures were tried as cheese starters in commercial factories under conditions where no protection for the starter against air-borne phage was given. The results were quite satisfactory for several months, but eventually there appeared in the commercial factories races of phage which would attack the phage-carrying culture and thus depress or completely check acid development in the cheese vats. It seems likely that the large number of phage races which evidently exist in nature would make a complete protection along these lines very difficult to accomplish.

Although it is known that several phage races, capable of developing on a certain strain of Streptococcus cremoris, exist in the surroundings of commercial cheese factories in New Zealand, only one specific race is invariably isolated from cheese or cheese whey when the culture is used as a starter. Laboratory and field evidence suggests that this particular race has a special affinity for the organism, and that its presence interferes with the growth of other races which could develop in its absence.

This note gives particulars of a method of determining the solubility of roller-dried milk powders which has been in use in the Department of the Government Chemist for some years. The figures obtained are empirical but are found to be a valuable aid in the comparative assessment of quality. The method is not claimed to be highly original, but appears to have aroused sufficient interest to justify publication. It is used in the Department for roller-dried milks only. For spray-dried powders a method is employed which measures the volume of deposit given on centrifuging similar to the Solubility Index test of the American Dry Milk Institute.

1. The mode of distribution of the constituents of centrifuged reconstituted whole-milk powder manufactured by different processes has been determined at 20 and 50° C.

2. Where considerable ‘insolubility’ exists, protein is carried into the fat layer and fat into the sediment layer in quantities directly related to the degree of ‘insolubility’. The fat in the sediment of roller powders appears to be associated almost entirely with the protein which remains insoluble at 50° C.

3. The sediments from reconstituted whole- and separated-milk powders made by different manufacturing processes have been obtained in bulk by vigorous centrifuging (14,500 × g). Analysis of these sediments reveals considerable similarity between them, and it is concluded that a well-washed sediment would consist mainly of denatured calcium caseinate together with calcium and phosphorus in the same proportions as in normal tricalcium phosphate, Ca3(PO4)2, the calcium caseinate and most of the calcium phosphate probably being in the form of a casein-phosphate complex.

4. The accuracy of some published methods of measuring milk powder solubility has been considered, and the inaccuracies arising from the non-homogeneity of the fat and sediment layers are stressed.