H.—34

14

extent with the magnitude of the actual change in outside-air temperature, and possibly with other conditions, such as air-circulation. Periods varying from fifty-five hours to ninety hours were recorded in three experiments. In a room with temperature varying in accordance with night and day temperatures the oscillations in temperature at the centre of the cheese are very slight compared with the change near the outer surface. This has yet to be correlated with changes taking place in the curd. Normal Loss in Weight of Cheese during Curing.—Since the beginning of experimental work the practice has been adopted of weighing the curd at milling, and the cheese as they come from the press, as well as at seven days, fourteen days, and when disposed of. These weights are all available but have not yet been correlated with texture. It is apparent from the studies that slit openness is dependent on more than the mere loss of moisture. The condition of the curd and cheese must also be considered. The bearing of the chemical composition of New Zealand milk and of the starter used, and the chemical changes occurring in the curd are being investigated. It is quite conceivable that the abnormal casein albumen ratio of New Zealand milk and the type of starter employed may be factors. These studies are very complex and they are not far enough advanced to report upon. Cracking of Cheese subsequent to Cutting.—This is most objectionable to the consumer. It would appear to be closely associated with maturity of cheese. Maturity is hastened by three conditions in practice—(a) Increase of rennet; (b) increased incorporation of moisture ; (c) increased curing temperature. Marked increase in moisture is to be avoided in export cheese for the purpose of avoiding slit openness and bad flavours. Age also increases maturity, but other factors affecting this without reducing quality should be investigated in view of the high, interest charges involved in holding cheeses. New Zealand cheese generally arrives in the export market by the time it is three or four months old. It is held at ordinary temperatures in factories for fourteen to twenty-one days, and thereafter held in cold storage at approximately 50° F. Home cheese is generally held in farm curing-rooms at ordinary temperatures till it is ripe, at from three to six or even more months old. It has been observed in the course of experimental work that cheese held at 50° F. from the time it is fourteen days old opens up badly at four months old when exposed to the air after cutting, while cheese held for a year at the same temperature scarcely opens up at all. Before considering the export of New Zealand cheese at higher temperatures it is necessary to know something of the temperatures in the holds of our transport ships. This has been investigated, and is reported on under the section dealing with the transportation of cheese. To throw definite light on the probable effects of transporting cheese at higher temperatures, or of holding cheese at higher temperatures for some time previous to export, well-made corresponding cheeses from a selected factory are being held at the College dairy factory at 50° F. and 60° F. respectively. Further information is being sought by holding cheeses in London stores at different temperatures. The effect of adding to cheese milk a culture of an organism isolated from ripe cheese was investigated by Mr. H. R. Whitehead with the object of ascertaining whether this organism, which was observed to be very common in ripe cheese, would accelerate the rate of ripening of cheese. The results proved disappointing. There was insufficient difference between the experimental and control cheeses to give promise that any advantage would be gained by addition of the organism to cheese milk. Small differences in flavour could be detected in the early stages of curing between the experimental and control cheeses, but these disappeared by the time both lots of cheese were ripe. The pasteurization of milk for cheesemaking has been questioned on the ground that it induces openness in cheese subsequent to cutting. Further accurate information is needed. It is known that the flavour of raw-milk cheeses deteriorates on keeping, even when made from good milk. There is no definite evidence that raw-milk cheeses from very pure milk, which would need to be used to safeguard flavour, crack less on cutting at the same age. Since no definite facts supporting the contention have yet been brought forward, and in the light of the work outlined above on slit openness, it seems probable from the examination made so far of cheeses that pasteurization has not a serious effect on the opening of cheese after exposure to air. Further research work on this point has been undertaken by this Institute. Summary of Openness Investigations — (I) There are three distinct types of openness —(a) Mechanical ; (b) slit; (c) fermentation. The cracking of cheese surfaces after cutting is another modification.' The causes of these three conditions may be independent of one another. (2) No distinct correlation has been found between high numbers of germs in milk nor between the amount of chemical constituents and openness of any kind. The nature of the organisms and of the milk constituents may, however, exert an influence. It is known that New Zealand milk differs from other milk in some respects. (3) Good pure milk gives the cheesemaker the best chance of making close cheese, though there is no guarantee that it will produce cheese free from slit openness. Farm inspection and payment for milk on the basis of purity are thus highly desirable. (4) Impure milk certainly deteriorates flavour, and may be conducive to mechanical openness. (5) Slow vats tend to induce mechanical openness. The cause of slow vats is not clearly known. (6) Milk from some districts is more difficult to make into close cheese then the milk of other districts. (7) Pasteurization of milk does not appear in preliminary investigations to be responsible for openness of any type. (8) Soft-bodied curds (curds excessively moist) are more conducive to slit openness in cheese than well-cooked curds carrying the necessary acidity. (9) Excessive salting injures cheese-body and delays maturity, though it tends to bring about closer texture.