Cultures of a strain of Streptococcus cremoris HP after maintenance in two countries under different conditions preserved their main characteristics unchanged for 18 years.

Samples of sterilized milk from fifteen dairies in the Midlands have been examined, and seasonal variations were detected in the incidence of mesophilic and thermophilic sporeformer contamination. Seasonal variation in the rate of spoilage at 30° C. was also apparent.

The lower incidence of contamination in summer was considered to be due to (a) less sporeformer contamination during milk production at the farm in the period when the cattle are not housed, and (b) increased processing times and temperatures in warm weather.

Cleansed milk bottles were examined and found to be an important source of contamination by mesophilic sporeformers, but the incidence of thermophiles of the type commonly found in sterilized milk was low.

Methods of reducing contamination in sterilized milk were discussed.

In order that the results recorded in Part II of this series(1) may have meaning, it is necessary to know the effect of different low concentrations of penicillin in cheese-making. Preliminary experiments suggest that this is mainly the result of their effect on the cultures used as starters.

During an investigation of the surface microflora of Stilton cheese during ripening, Brindley(1) isolated lactobacilli from the surface scrapings of normal and slipcoat cheese. Some of these isolates were sent to the National Institute for Research in Dairying to form part of a collection of lactobacilli which was being built up for classification purposes. During the work on classifying lactobacilli these organisms from Stilton cheese were examined and all but one were serologically grouped and identified by physiological tests. They were also tested against a number of type sera which were available, and it was found that, although isolated fromcheese of different origins, most of the strains belonged to the same serological type.

Experience in the use of a rapidly growing culture of Streptococcus thermophilus for the assay of traces of penicillin in milk is described.

A comparison is made of the stripping characteristics of the types of plant studied in previous papers of the series. The effects of alterations to the type of plant, the number of vessels used or a change in processing conditions on the volatile flavour components are illustrated by calculations for solutes having equilibrium coefficients m of 2, 10 and 50. For design purposes a hypothetical taint of m=10 is used, the final taint concentration being set at 10% (of initial) for high-taint pastures and 25% for low-taint areas. Using the above hypothetical conditions, calculated steam-demand figures are shown to agree with known typical steam-demand values. The use of a flash cooling vessel is examined and shown to effect a useful steam saving.

The effect of steam velocity on the mechanical break up of the liquid in a counterflow spray column is shown; an increase in steam flow increased the liquid side disturbance and thus reduced the liquid side resistance giving a greater rate of taint transfer, the characteristic thus more nearly following a line of constant saturation than a line of constant number of transfer units.

A number of flow circuits for deodorizing plant are described. The general conditions limiting the continued reduction in steam flow are discussed.

The addition of penicillin to cheese milk had the effect of delaying acid production by starter in the cheese curd; any effect on cheese quality could be traced to the delay in acid production and to a high final pH in the cheese. There was no indication of any direct effect of penicillin on the ripening process.

A concentration of 0·10 unit/ml. of penicillin in the cheese milk was a borderline amount with the particular starters which were used. Cheese quality was sometimes adversely affected. A smaller concentration (0·05 unit/ml.) delayed the cheese-making process slightly but had no adverse effect in final cheese quality. Higher concentrations regularly resulted in poor quality cheese.

Penicillinase added to cheese milk neutralized any penicillin present but with a short time of contact of about 30 min., a large excess of penicillinase had to be used.

The rate of acid production by a slow variant of Streptococcus cremoris in milk was raised to that of the fast parent strain when peptone or acid hydrolysed peptone were added. Lactose utilization was similarly affected. However, the stimulation took place without any change in the rate of growth. Other sources of available nitrogen gave similar results.

It is concluded that the change from a fast to a slow culture which occurs on continued transfer is due to the loss of ability to utilize the nitrogen compounds of milk.

An examination of over 5000 milk samples has shown that penicillin is frequently present. Its concentration, however, is usually below the level which is believed to be necessary to cause significant interference in cheese-making, but a significant proportion of the samples contained more than a third of this quantity. This suggests that conditions under which difficulty would arise are not remote.

Cultures of sporeforming bacteria isolated from commercially sterilized milk were examined and seasonal variations in the incidence of B. subtilis/ B. licheniformis strains were apparent which may account for the increased rate of spoilage at 30° C. during the winter.

B. subtilis was the most common mesophilic sporeformer isolated, and under favourable conditions it produces rapid digestion of milk.

Thermophilic sporeformers are frequently present, and usually produce a firm acid clot in milk held at temperatures favourable for their growth. The classification of the thermophiles isolated is uncertain and a review of the classification of the aerobic thermophilic sporeformers in general is required.

Cl. thermosaccharolyticum, a gas-producing thermophile, was isolated from sterilized milk.

9234 cows in 524 herds were divided into two groups in each herd, those holding to first service and those not holding to first service. The differences between the milk-yield means of each group in each herd were tested by an analysis of variance procedure, which showed no significant difference in milk production between the two fertility levels. It was also shown that the sample was homogeneous. The study shows that the amount of their milk yield during the month of service does not adversely affect the fertility of dairy cattle.