H.—34.

(d) Cheese-rind Investigations (R. M. Dolby). —The occurrence of cracks in cheese-rind by permitting the entry of mould may cause the spoilage of a considerable portion of the cheese. Under present conditions, when delays in transport may increase storage periods, such defects may be accentuated. Investigations both in the Institute factory and in a commercial factory have shown that cracks are most likely to develop during the first week after manufacture, when the knitting together of the curd particles is still incomplete, and that cracks do not usually extend appreciably after the cheese is two weeks old. The experiments demonstrate the necessity of using an outer bandage which is in good condition and of avoiding wrinkles in the inner bandage. Other factors tending to produce rind cracks are the placing of cold curd in the hoops, inadequate pressing, oversalting of curd, displacement of curd where morning dressing is practised, and damage to cheese by rough handling after removal from the hoop. Normal variations in moisture content of curd or in temperature of curd at hooping did not appear to influence the development of cracks in'the rind. The omission of scalding of the hoops, while reducing the adhesion of the bandage, did not cause increased cracking. Storage at high temperatures and low humidities, and storage in a current of air, also did not produce cracks in the rind. (e) Standardization of Annatto (C. R. Barnicoat). —Further evidence has been accumulated to support the view previously put forward that annatto extract (cheese colour) is best standardized in alkaline solution by examination in transmitted light. (/) Controlled Temperature and Humidity of Cheese-curing Rooms.—See section " Mycological Projects." Buttermaking Projects. (a) Land Cress and other Feed Taints in Cream (F. H. McDowall).—lt has been previously reported that land cress on steam distillation yields an oil of high boiling-point and consisting for the most part of benzyl cyanide. Addition of the oil in small proportions to cream used in buttermanufacture gave a flavour in the butter which had some resemblance to land cress taint but which was not true land cress taint. Treatment of cream tainted with land cress in the small Vacreator at the Institute was effective in removal of taints of medium intensity and in reducing to small proportions the taint of heavily tainted cream. An attempt was made in a commercial factory to obtain similar results by use of the large-scale Vacreator. It was found that the large machine was less efficient in this respect, and some modifications introduced by the makers were tried out. The preliminary trials showed that the modifications gave an improvement in the degree of taint removal. Arrangements are now in hand for a large-scale trial during the period of cress taint incidence in the coming season. The Vacreator modifications also increased the efficiency of removal of feed (clo.ver) taint. It has been shown that taint from land cress passes into the milk in the udder within thirty minutes after consumption of the plant by the animal, and that it persists in the milk for several hours, and sometimes for more than twelve hours. The period of persistence of the taint in the milk and cream varies to some extent, however, with the individuality of the animals. (b) Keeping Properties of Butter (C. R. Barnicoat). —(i) Temperature of Storage and Addition of Anti-oxidants : A study has been made of the keeping qualities of New Zealand finest-quality butter held at temperatures above freezing-point, in order that information on this subject should be available if required. It was found that butter containing 1-5 per cent, salt had a better keeping quality on storage at 35° F. than butter treated with various anti-oxidants and preservatives. Finest salted butter held for four months at 35° F. usually graded 90-91 points after storage. After removal to room temperatures, however, there was a. rapid deterioration ' hence butter held for any considerable length of time at temperatures above freezing-point should be passed on to the consumer as soon as possible after removal from storage. (ii) Metallic Contamination : It was shown that the presence in cream of 0-6 parts of copper per million had a pronounced effect on the quality of the resultant butter stored at 14 1. After one week the grade had been lowered by half a point, after five months by one point, and after twelve months by two points and a half. Iron (both ferrous and ferric) present in the cream to the extent of three parts per million had only a slight effect. The importance of keeping cream and butter away from bare copper surfaces is thus emphasized. (iii) Effect of Light: It has been observed that in some butter-factories there are skylights through which direct sunlight can impinge on the butter in the making-room. It is known from work here and elsewhere that light accelerates the deterioration of fat. Some experiments have been carried out to study the effect of light of varying intensities on butter under conditions of handling similar to those existent in commercial factories. Blocks of butter exposed to light were found to undergo oxidation at the surface. When this butter was passed through the packing-machine and the surface layer was thus mixed into the remainder of the butter by the action of the packer screws, the evidence of deterioration disappeared. The butters are being held in cold storage for some months The gradings of the stored butter, when they become available, will be of interest, as they should indicate whether the incipient deterioration noted on the surface of the block has spread through the whole mass of the butter. (c) Hardness of Butter (R. M. Dolby).—(i) Apparatus for Measurement: A new apparatus for measuring hardness has been developed. This instrument, which determines the resistance of butter

2—H. 34.

9