H.—34.

9

time new dairying districts have been opened up, more intensive farming practices have been adopted, and modifications in standard manufacturing practice have been introduced. It is just possible that the correlation of these factors with the increase in the prevalence of openness may eventually throw some light on the cause of the trouble. It is conceivable, for instance, that there is something inherent in the milk of certain districts which renders the manufacture of close cheese a very difficult matter. It is surely more than a coincidence that experienced factory-managers, who always aim at quality, have encountered difficulties they cannot surmount. Many cases are known of factory-managers who have been able to manufacture finest-grade cheese in one district, yet they have been unable to get similar results in another, although they applied just as much skill and care in their work. Types of Openness.—ln the course of experimental work it has become plainly evident that there are three distinct types of openness ; and to these a fourth may be added, if there is taken into consideration the texture of the cut surface of the cheese after it has been exposed for a few days. It is necessary to consider these types individually before proceeding to discuss them, because there is some evidence that one is not necessarily related to another. There are times when only one type is present in a cheese, and at other times two or even more types may be observed in any one cheese. (a) Mechanical openness : This takes the form of holes of varied size and distribution. The holes may be confined mainly to one part of it. In all cases it is usually possible to discern the outline of the original curd-particles. This gives the impression that the curd-particles have never been pressed together. This is undoubtedly true, for such openness may be observed when a cheese is bored or cut immediately after being taken from the press. Fat may be present in some of the holes, but usually it does not fill up the whole of the cavity. There are at present no data to indicate whether the occurrence of the fat represents cause or effect of openness. (b) Slit openness : This takes the form of slits in the body of the cheese, and often occurs in cheeses which are quite free of mechanical holes. The slits, again, are of varied, size and distribution. Sometimes they may be only a mere fraction of an inch in length ; at other times they may be 2 in. long, or even more. They occasionally appear to follow the line of junction of the original curdparticles, but they just as frequently arise in the centre of the curd-particles. They also occur close to mechanical holes where lines of weakness exist in the cheese. These holes are quite small at first and gradually enlarge, becoming usually irregular in shape. They are not present in the cheese when it comes from the press, but develop any time afterwards between the third and possibly the twentieth day after being taken from the press. A certain amount of this type of openness has possibly been attributed to fermentation. There is no direct evidence to show that fermentation is responsible. The reason for attributing it to fermentation is possibly the fact that these slits have been found in cheese with abnormal flavours. In this connection it has to be remembered that abnormal flavours may be observed in cheeses which are perfectly close, and, conversely, no abnormal flavour may be observed in cheeses with this defect. This type of openness is possibly the most difficult to deal with, because it can appear in cheeses which are very well made. (c) Fermentation openness : The openings in this case have generally a more regular outline than in the other types, varying in size from mere pin-holes to holes the size of a grape. The shape may be round or somewhat slit-like. Yeasts have often been shown to be responsible for this condition ; certain types of gas-producing germs have also been found to be a cause when no starter, or an inactive starter, was used in making the cheese. This type of openness has not been experienced in Our experimental work, and there is no evidence to show that it is of widespread occurrence. It must, however, not be overlooked. (d) Openings arising after cheese is cut : It occasionally happens that after a cheese-surface has been exposed for some time large openings will appear throughout the body of the cheese. This may happen to a cheese which at the time of cutting is perfectly close in texture. This condition is most disconcerting to the grocer, because its appearance is unattractive to the consumer and the cheese dries up quickly. Cheeses which are affected with slit openness are particularly liable to this fault. Looseness : Closely akin to these distinct types of opening is the conditions of cheese known as " looseness." In this case fractures can be observed in the body of the cheese without any cavities being present. Slit openness often follows upon looseness. Probable Causes of Openness.—At the outset of experimental work on the problem these distinct types of openness were not generally recognized, and therefore in the course of mapping out a scheme of work general impressions of any conditions that would .possibly cause fractures in the cheese had to be used as a guide. The probable causes were grouped into four main classes : — (1) Possible chemical and bacteriological peculiarities of the milk : (2) Details in manufacture : (3) Methods of pressing cheese : (4) Methods of curing cheese. In view of the impossibility of analysing all of the groups and their many complexities simultaneously, there had to be sought some outstanding difference between methods of manufacturing cheddar cheese in New Zealand on the one hand, and Canada and Britain on the other, since it is reported that Canadian and British cheeses are not so subject to openness as is the New Zealand product. The outstanding difference is that. 90 per cent, of the Dominion product is made from pasteurized milk, while Canadian and .Home cheese are made from raw milk. Since any manufacturing studies would need to be carried out with pasteurized milk to be in keeping with factory practice, it was decided to study closely the effects which pasteurization of milk has upon cheese-texture. In conjunction with this work it was decided to make a survey of the chemical and bacteriological condition of milk supplied to factories in the Manawatu district, so that a comparison could be made between factories badly affected with the trouble and those more fortunate.

2—H. 34.