DAIRY RESEARCH.

Manawatu Standard, Volume LVI, Issue 182, 3 July 1936, Page 5

DAIRY RESEARCH.

WORK OF THE INSTITUTE. ADDRESS BY DR Me DOW ALL. Dr F. 11. MeDowall, of the Dairy Research Institute, gave an address to the annaul conference of the South Island Daily Association at Dunedin. | During this year the institute, he i thought, could claim a good measure j of progress towards the ideal of elminating the difficulties which beset the manufacture of dairy produce, and of still further enhancing the general quality level of New Zealand butter and cheese. CHEESE FAULTS. •'I lie problem of openness in cheese was one of the first which had engaged the attention of the institute when it had been established. During several years of work it was shown that none of the popular theories ■ of the cause of this defect provided an adequate explanation. It was shown by practical cheesniaking experiments that openness was held in check to some extent when only clean milk of the finest quality was used in the vats and when acidity production in the vats went steadily forward. Certain other details of manufacture. such as care in packing in the hoops, and salting conditions, had a slight influence on the texture, but in the main the trouble could not be avoided even b.v the use of the best milk, ami the ultimate cause could not he defined. He was happy to be able to say that after merely reporting progress for so many years they had at last been able to track down the factor responsible for the formation of slits in cheese that was otbenvise of _ good quality. This factor was bacteriological. All milk contained a bacteria of a certain type called lactobacilli. These germs were found in small numbers only and they grew very slowly in milk and were difficult to detect even in the freshly made cheese. They began to grow in the cheese when it was two or three weeks old, and ultimately they became the predominating type of germ. Their presence in cheese was of g-cat importance, since they had a very marked influence on its final flavour. There were, however, several varities of these bacteria. For their purpose they might be divided into three types:— 1. Those which produced desirable cheese flavours.

2. Those which gave the fruity flavours which in the past lias been ascribed to the action of yeasts.

3. Those which had the property of producing considerable amounts of carbon dioxide gas.

Tt was this third or gas-producing varietv which had been shown to have an influence on the occurrence of slits in the cheese. They were isolated from the cheese in the neighbourhood of slits and were shown to produce gas when grown under laboratory conditions. They wore then added deliberately to cheese mill;, another portion of the same milk being made into cheese os a control. Several strains of bacilli of this type had thus been shown to produce a marked slittiness in cheese after the ripening period, whereas the control cheeses were relativly close. Tt appeared, therefore, that whereas the fermentation which sometimes produced round ho'os in cheese was caused liy germs such as bacillus coli, which grew rapidly in milk and curd during the manufacturing process, the slittiness which affected their cheese on some occasions was caused by the lactobacilli which developed later in the life of the elieese when its body had become too firm to permit the formation of a round hole. The gas formed forced the cheese body apart in the form of slits. So much for the cause of the trouble. What was the remedy ? The cleaner the milk as it was produced on the farm the smaller would he the number of bacilli in the mill; and the less the chance of openness occurring in the cheese. But it was difficult to ensure that the gas-producing lactobacilli would be quite absent, and even when only a few were present they would grow rapidly in the cheese as it rii>eiied if the conditions were favourable. The only practical remedy so far in view was the maintenance of unfavourable conditions. It had been observed during the past season that the type of starter used in the cheese vat had a marked controlling influence on tlic development of this ty]>e of openness. The active sing'e cultures developed at the institute permitted the elieesemaker to follow a system of manufacture which seemed to hold in check the activities of the gas-produc-ing lactobacilli which might be present in the milk. Reports from many factories indicated that where a change was made from a moderately active mixed stater culture to one of the institute’s pure strain active cultures,: there was an immediate decrease in tiie extent of openness, and that was reflected in the grade of the cheese, ’['here were therefore these perfectly practical means for the' improvement of cheese:—

1. Careful and conscientious gradini' ol tlie milk. 2. Development of the use of really active starters which permitted the eheeseuiaker to follow the best process of manufacture. MAINTENANCE OF ACTIVE STARTED S. They were still hampered in this la tter particular, however, by. the unreliability of active starters, said' Dr McDowall. The institute had been able to devise methods for selecting the best germs for use as cheese starters, and the preparation of starters was ■ no longer a matter of trial anrl error. Some of their cultures were wellknown to managers, who found them iniifnitely superior to cultures which had been in use in the past. This in itself represented a big stop forward. But it was still not possishle to. ensure that these cultures would remain active in all factories. They had the disturbing habit of failing suddenly with 'ittle or no waning to the factory manager. Their work had do-, finite’y made clear what was. the ultimate cause of the trouble, but at present they were unable to provide a satisfactory remedy. Tlie.v had shown that the sta-ter bacteria were susceptible'.to the action of a vi us called bacteriophage (which was really what might be termed a bacterial disease) in "all probability produced by the germs themselves under the influence of the particular conditions under which thev were g own. The indications were that some at present unknown property of particular milk supplies came into play. They were, howeven still unable to define a method of selecting a mi'k supnly capable of maintaining a starter free from the attack of the bacteriophage, hut they, believed that ultimately .'means would be found to this end. During the past season two methods for avoiding starter failures had been tried with some success. Mr Wards, the manager of' the Rexdale Dairy -Company ."bad 'developed a method of testilia out starters before they were used inutile vats. He was thus forewarned, and was able to avoid the usp of dead starters, and consequently spoilage of (•’’oese. The use of this method euab'ecl managers to avoid trouble on many occasions, hut it was not entirely reliable. Other factories had

found that cultures maintained their activity with them for a definite period, | and with regular fresh supplies from J the laboratory they were able to avoid ! , trouble. Both of these methods had : proved helpful, but they were certainly | not a complete solution. The position | was therefore that they had the means ! of selecting the best types of starter culture which in many factories gave excellent results, with little or no trouble throughout the season. In other factories a difficulty occurred, for which at present they' had no solution, but only certain palliatives. There was little doubt that in time they would be able to overcome this difficulty, and it would then be possible for managers to maintain active starters lor long periods and to make a more even lino of cheese from day to day.