The presence, in the cheese milk, of phage active against the organisms of the ‘singlestrain ’ culture in use as starter leads to its multiplication during the cheese-making process. The extent to which the presence of phage is made evident in the vat depends largely upon the amount of initial infection. A heavy infection permits sufficient multiplication of the phage to cause lysis of the organisms and consequent cessation of acid development before the manufacturing process is completed. A light infection may have no noticeable influence upon the performance of the starter in the vat. Intermediate amounts have an effect on the rate of acid development in the later stages of the process, but within certain limits there is little adverse influence on the quality of the cheese produced.

Several cheese made from milk after the starter had failed, or during outbreaks of ‘slowness’ at three different places, were found to contain bacteriophage, which it is now possible to isolate from cheese where the whey is no longer available. The concentration of phage in cheese was found to be fairly constant when tested periodically during one year. The significance of such persistence on phage dispersal, its reintroduction into the dairy, and carry-over from one season to the next is pointed out.

1. Bacteriological studies have been made of some 400 samples of dried milk products comprising roller-dried separated milk, roller-dried full-cream milk, roller-dried buttermilk, roller-dried whey and spray-dried whey. The samples were derived from a total of plants operating throughout Great Britain.

2. The mean values for the plate counts at 37 and 55°C. of the roller-dried products were all below 1000 per g· as against ½–2½ million at 37°C. and 10,000–30,000 at 55°C. for the spray-dried products. The spray-dried products also gave three times as many positive presumptive coliform tests at all dilutions as did the roller-dried products.

3. The roller-dried whey and the roller-dried buttermilk both gave more variable counts at 37°C. and higher counts at 55°C. than the roller-dried separated milk and the roller-dried full-cream milk. The spray-dried whey gave higher and more variable counts at both 37 and 55°. than the spray-dried milk.

4. Marked differences were observed in the plate counts of samples derived from different plants, some plants giving consistently low counts and others giving higher and more variable figures. Differences were also observed in the counts at different stages of handling.

5. Evidence was obtained which indicates that mould counts do not provide a reliable indication of recontamination subsequent to drying.

It is evident from the foregoing results that decreases in count may occur during the storage of milk and whey powders. The extent of this decrease varies, however, with the type of powder and even between different samples of the same type. Further, many samples may show little or no alteration in the numbers of viable organisms surviving storage even for considerable periods.

Nevertheless, it is obviously important that for grading purposes or in relation to plant control a time limit should be fixed within which the plate count of any milk or whey powder should be determined. No data are available to show how rapidly organisms may die out during storage periods of less than 3 months, but it is tentatively suggested that all powders should normally be examined within, say, 14 days of manufacture. Unless such a limit is fixed, those samples in which the count does fall appreciably would reflect too favourably on the conditions of manufacture.

1. Full-cream unsweetened condensed milk (evaporated milk) and full-cream sweetened condensed milk (condensed milk) were prepared simultaneously on several occasions each time from a common bulk of raw milk. Heat treatment in the preparation of evaporated milk is, of course, much more severe than with condensed milk.

(a) There was no loss of vitamin A, carotene or riboflavin in either of the processes.

(b) The mean loss of vitamin C as compared with the raw milk was 10% for condensed and 60% for evaporated milk.

(c) The vitamin B1 losses were 3·5 and 27% respectively.

(d) Tests on rats showed that the biological values and true digestibilities of the proteins of the raw, condensed and evaporated milks were respectively 85·6 and 94·2, 84·6 and 98·8, 84·1 and 93·7. The differences in biological value are without statistical significance but the digestibility of the condensed milk was significantly higher than that of the other two milks.