The volatile sulphur compounds present in New Zealand Cheddar cheese have been studied by means of gas entrainment and steam-distillation techniques. Hydrogen sulphide was the only sulphur compound which could be detected, and after removal of this compound from the gas stream or steam distillate only a mixture of carbonyl compounds remained. Subsequent removal of these compounds completely destroyed the original cheesy aroma of the gas stream or distillate.

The parts played by hydrogen sulphide and carbonyl compounds in Cheddar cheese flavour are discussed.

The author wishes to record his gratitude to Dr H. R. Whitehead and Dr W. A. McGillivray for their helpful advice and criticism and to Mr P. L. McLaughlin for technical assistance.

Lactose was estimated accurately and rapidly in casein by use of anthrone reagent on the clear filtrate from precipitation of a sodium bicarbonate solution of the casein with 0·1 n-sulphuric acid. The reagent consists of 0·15% (w/v) anthrone in 70% (v/v) sulphuric acid. The ice-cold anthrone solution (10 ml.) was added, with cooling, to 1 ml. of the ice-cold solution containing 0–100 µg. of lactose. The mixture was heated at 100° C. for 6 min. and cooled for 30 min. The optical density of the coloured solution was then measured at 625 mµ

1. When the concentration of fat-free milk-powder is increased, other factors being kept constant, the elastic and viscous setting-parameters of the curd also progressively increase, being related to the concentration by power-equations. The intercepts, which correspond closely to ‘coagulation times’, likewise increase, but nearly linearly with concentration

2. These effects depend mainly on protein concentration. Quite large quantities of added lactose make little difference to the parameters.

3. The slopes of the logarithmic setting curves vary quite independently of their intercepts, so that ‘coagulation times’ provide a very incomplete indication of the rate of setting of curd.

4. A comparison of setting data obtained in the ordinary way at a series of temperatures with those from experiments in which the rennet is first allowed to act on the milk at near freezing-point, show that, in the latter case, there is considerable delay before the normal equation of setting is established in the curd. It is also clear that high temperatures are detrimental to this process of setting, just as they are when the usual procedure is followed.

5. The general law that the rate of setting is, at any time, proportional to the amount of still unset casein, is established much sooner if the time zero is defined in such a way as to take all the processes involved together. If an ‘induction period’ is subtracted, either by letting the rennet first act in the cold, or by taking the time zero in the normal process at the coagulation, and not the renneting, time, a much longer time elapses before the curves become linear.

We are indebted to many colleagues at the N.I.R.D. for helpful discussions, especially Dr S. J. Rowland and Dr R. Aschaffenburg.

1. The partition of riboflavin between the free and the protein-bound forms was measured in the milk of six Ayrshire cows, three of which were treated with l-thyroxine.

2. As lactation progressed there was a slow decline in the total riboflavin content of the milk for which the initial values were 0·86 to 1·09 µg./ml. milk. The rate of decline ranged from 0·01 to 0·003 µg./ml. milk per day.

3. Thyroxine had its expected effects in stimulating milk yield and heart rate, and in preventing the rise of phosphatase in the milk as lactation progressed, but it did not affect either the concentration or the partition of riboflavin.

4. Reasons are advanced for the marked contrast between the effect of thyroxine in increasing the phosphorylation of thiamine and the absence of any such effect on riboflavin.

We thank Miss S. McLauchlan and Miss M. Lightbody for technical assistance, and Glaxo Laboratories Ltd., Greenford, Middlesex, for a gift of L-thyroxine.

Slices and blocks of cheese were coloured with aqueous methylene blue solution and vacuum-packed or wrapped in the films to be compared. The extent of bleaching of the dye after 14 days gave a good indication of the extent to which oxygen was excluded by the film. Similar results were obtained with vacuum-packed slices and with wrapped rindless cheeses.

With polythene-coated and wax-coated MSAT cellophane films there was little or no reduction of methylene blue on the cheese surface. Similar films, including a lamination of foil or MXXT cellophane, allowed complete or almost complete bleaching.

1. Under carefully standardized conditions, the increase in the over-all rigidity modulus of curd when the time after rennetting is doubled, varies inversely as the cube root of the rennet concentration. The intercepts of the extrapolated setting curves on the time axis and the observed coagulation times vary inversely as the concentration.

2. With the same (normal) rennet concentration, some rheological parameters increase or decrease progressively as temperature is increased from 21° to 41° C.; others pass through maxima or minima, all between 29° and 35° C.

3. Long-term ‘creep’ experiments have been done over the above temperature range, creep and slow recovery increasing progressively with temperature. Relaxation experiments, though showing the simplest distribution of relaxation times at about 32° C., are too greatly influenced by unavoidable differences in firmness at the different temperatures for it to be possible, at this stage, to draw conclusions about their temperature dependence.

4. A comparison of some of these results with data published by a few other workers is attempted.

It has been shown that the lactose concentration in separated milk can be determined rapidly with an accuracy of ±1·5% by infra-red absorption methods, using wavelengths in the 10μ region.

The method can also be used to determine lactose in condensed whey and should prove applicable to continuous recording techniques.

1. Results are reported of an experiment with fattening pigs carried out under commercial conditions, to obtain further information on the comparison of all-meal feeding with meal plus unrestricted amounts of whey. In addition, the effect of omitting the antibiotic, oxytetracycline, from the diet during the latter half of the fattening period was investigated.

2. There were four treatments. (i) Meal only ad lib. up to a daily maximum of 6 lb./pig, with oxytetracycline included in the diet for the whole fattening period. (ii) As (i) but oxytetracycline included in the diet only up to an average pen live weight of 130 lb. (iii) 3 lb. meal reduced to 2 lb./pig/day by 13 weeks of age plus unrestricted amounts of whey with oxytetracycline included in the basal meal for the whole fattening period. (iv) As (iii) but oxytetracycline included in the diet only up to an average pen live weight of 130 lb.

There were five pens of nine group-fed pigs on each treatment, involving a total of 180 pigs. The pigs were on experiment from approximately 8 weeks of age to bacon weight. Comprehensive carcass measurements were made on all pigs.

3. The meal plus whey-fed pigs grew significantly slower and utilized their food significantly less efficiently than those fed meal only. They also had a significantly lower dressing percentage, but longer and less fat carcasses than the all-meal fed animals. The results are discussed in relation to those obtained in earlier experiments completed under similar conditions at the Cow and Gate farm.

4. Comparison of the efficiency of food utilization results of the all-meal and meal plus whey-fed pigs showed that 1 gal. of whey replaced approximately 0·7 lb. of meal.

5. The results showed that omission of antibiotic from the diet of either the all-meal or meal plus whey-fed pigs after they reached 130 lb. live weight, had no significant effect on growth rate, efficiency of food utilization or any carcass measurements of the pigs.

We wish to thank the Director of Messrs C. and G. Prideaux, Ltd., Bacon Curers, Motcombe, Shaftesbury, Dorset, for permission to take carcass measurements of the experimental pigs, and we are greatly indebted to Messrs K. Lawrence and P. Prideaux who most conscientiously took these measurements.

The numbers of lactobacilli present in milk for cheese-making and in the cheese at various stages of ripening, have been determined for 38 Cheddar cheeses made during studies on flavour enhancement. These organisms multiplied rapidly even during the first few days of curing. Maximum levels were attained at 3–6 months; at 1 year counts had declined appreciably.

Flavour intensity in the experimental cheese appeared to be correlated with the level of lactobacilli present in (a) milk at the start of cheese-making and (b) at subsequent stages of ripening. These two count levels were usually closely correlated. Factory raw milk had the highest counts and gave the highest degree of flavour, followed by similar milk pasteurized and inoculated with selected strains of lactobacilli.

1. The administration of 0·5–1·5 kg. sodium acetate to cows in which the milk fat percentage had been reduced by diets low in hay and high in concentrates usually brought about an appreciable improvement in fat percentage. The extent of the response varied from slight to complete. The Reichert value of the milk fat fell with diets low in hay, but was raised by administration of acetate.

2. The daily administration of 500 g. sodium acetate to cows receiving diets containing normal levels of hay and concentrates according to their milk yields did not affect the milk fat content.

3. The daily administration of 414 g. sodium propionate did not restore fat percentages lowered by the diets low in hay. Butyrate appeared, in a test with one cow, to possess the restorative properties of acetate.

4. With diets containing either 50 lb. silage as the sole roughage or 60 lb. fodder beet and only 6 lb. hay, fat percentages were the same as with a normal diet containing 16 lb. hay.

The heat resistance of strains of lactobacilli previously isolated from Cheddar cheese was determined using a laboratory pasteurization test and a commercial pasteurizer.

The laboratory tests showed variations in heat resistance at 140° F. for 10 sec. which were not correlated with species, but at 150° F. for 10 sec., an average of 99·55% destruction occurred with all strains.

With the commercial pasteurizer, heating at 155° F. for 17 sec. caused a 99·99999–100% destruction, whilst heating at 160° F. for 17 sec. destroyed 100% of all strains of lactobacilli tested in every case.

We wish to thank Miss H. R. Chapman and Miss A. J. W. Harrison for operating the pasteurizer.

1. It is possible to study the structure of cheese curd and the disposition of microorganisms therein by microscopical observation of sections cut on the freezing microtome after fixation in formalin.

2. In the small number of cheese examined bacterial colonies were found only in crevices.

3. As ripening proceeded the finer protein structures tended to disappear.

4. The distribution of bacteria in cheese curd is markedly uneven.

1. An experiment to investigate the seasonal increase in the solids-not-fat content of milk, which usually occurs in Britain when cows go from winter feeding to spring grazing, is described.

2. Two similar groups of cows were fed good quality winter rations at the same high level both before and after calving (about 115% of the Woodman standard after calving), until spring grass was available. One group of 7 cows was then fed for 6 weeks almost entirely on cut grass, returning to winter rations for a further 3 weeks. The control group of 6 cows continued to be fed throughout the experiment on winter rations and both groups remained indoors for the whole of the experiment. The estimated nutrient intake of both groups in all periods was kept substantially constant.

3. Changes in milk yield and composition were mainly those associated with advancing stage of lactation, and grass feeding had little specific effect. It is concluded that the increase in milk protein content which is normally observed soon after the start of spring grazing probably results from an improved plane of nutrition and not specifically from an increase in the intake of soluble carbohydrates.

4. Increases in the total nitrogen content of the milk as the experiment proceeded were contributed to uniformly by the casein, total albumin and β-lactoglobulin fractions.

Theoretical and practical aspects of the apparent or effective viscosity of milk have been studied by many workers: see reviews by Scott Blair(1,2,3). Seidler & Elke(4), Cox(5), and others have considered the relations between observation temperature and viscosity measurements; Mohr & Oldenburg(6) and Puri & Gupta(7), for example, have investigated the effects of differences between individual viscometers. Other workers, including Puri & Gupta(7), Kobler(8) and Spöttel & Gneist(9), have examined the viscosity of whole raw milk after different times and temperatures of storage; and Weinlig(10), Trout & Weinstein(11) and Whitnah, Rutz & Fryer(12,13) have studied changes in viscosity values in connexion with various processes such as pasteurization and homogenization.

The accuracy of the method specified in B.S. 734:1937 for the estimation of the total solids and solids-not-fat contents of milk from the density and fat content has been assessed by direct comparisons with the gravimetric method. A total of 2425 samples of milk, mostly from single herds, were examined in five series over different years.

The percentages of solids estimated by the density method were lower, by an average of 0·06, than those determined gravimetrically. To correct for this error, and to compensate for the lower, more accurate fat percentages arising from the recent reduction in the capacity of the Gerber milk pipette, it was proposed that the density formulae be modified to T=0·25D+l·22F+0·72 and S.N.F.=0·25D+0·22F+0·72.

These formulae were adopted in October 1957 in an amendment to the B.S. 734 published in 1955.

Butterfat has been shown to contain the normal odd-numbered saturated acids n-nonadecanoic acid (C19), n-heneicosanoic acid (C21), and n-tricosanoic acids (C23).

The presence of the normal even-numbered acids n-octadecanoic acid (C18), n-docosanoic acid (C22), n-tetracosanoic acid (C24) and n-hexacosanoic acid (C26) is conclusively established.

n-Eicosanoic acid (C20) formerly assumed to be present in butterfat has been isolated and identified by its physical and chemical properties.