Milks were prepared at 1-7-to 4-fold the initial concentration by combining skim-milk concentrated by ultrafiltration with cream, and used for Cheddar cheese-making. Starter growth was unaffected, but the increased buffering capacity in the more concentrated milks resulted in a slower decline in pH and a higher pH value in the cheese. Curd formation was faster despite the use of reduced amounts of rennet. With milk concentrated more than 2-fold, large amounts of fat were lost in the whey, so that the cheeses had less fat than normally. Fat losses may be partly related to the lower degree of aggregation of the casein micelles when the curd was cut. As the concentration factor of the milk increased, the rate of casein breakdown, the intensity of Cheddar flavour, and the levels of H 2 S and methanethiol in the cheese decreased. These factors may relate to the reduced concentration of active rennet retained in the curd at pressing.

Whole milk was concentrated by ultrafiltration in a plant causing some homogenization of the fat. Comparisons were made with milk concentrated in a plant causing little homogenization and with milk homogenized conventionally. None of the processes appreciably affected the casein micelle size distribution. On rennet treatment of homogenized milk, casein micelle aggregation occurred more slowly, the protein network in the curd was less coarse and the rate of whey loss was reduced, compared with non-homogenized milk at the same concentration. In using concentrated milks for cheesemaking homogenization improved the composition of Cheddar cheese, because of increased fat and moisture retention, but curd fusion was poorer. Some aspects of the texture of the mature cheeses were improved, but the free fatty acid levels were higher. Values for the firmness of curds, formed from milks processed in different ways, did not relate to the extent of aggregation of the casein micelles. It is suggested that the complete cheesemaking process is driven by the tendency of the casein to aggregate.It is well established that milk composition and treatment affect cheese body and texture (Davis, 1965). This appears to be due to effects on both cheese composition and the microstructure of the coagulum. The latter seems to be a major factor determining the structure and texture of cheese (Green et alAQ8lb).Both concentration by ultrafiltration and homogenization influence the cheesemaking properties of milk and cheese texture. Cheese made with concentrated milk tends to be hard and granular, because of excessive segregation of the fat and protein resulting from a coarser than normal protein network, with high fat losses occurring during the manufacture (Prokopek et al. 1976; Green et al. 1981a;Shimmin, 1982). Homogenization of milk reduces both curd firming and syneresis, so more moisture than normal is retained in the cheese. It also results in increased fat retention (Davis, 1965) and a softer, smoother and more elastic cheese (Emmons et al. 1980).The aim of this work was to investigate whether the adverse effects of using concentrated milk for cheesemaking might be overcome by introducing a homogenization step. The first part of the paper describes the effects on the milk of processing in 2 ultrafiltration (UF)-plants and the effects of concentration with or without homogenization, and also conventional homogenization, on the formation, structure and properties of curds. The second part describes the cheesemaking properties of milks processed in the 2 UF-plants, with and without much concentration.

The results are presented of two experiments in which the quality of samples of bull semen was assessed by a number of laboratory tests and then correlated with the 112-day non-return percentage obtained by the use of those samples in A.I. The results reveal the inadequacy of the laboratory tests used as methods of predicting the fertility of semen samples but show that limits may be set outside which poor semen samples could be discarded.

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Whole milk was concentrated by a factor of two by ultrafiltration. It was used directly for making Cheddar and Cheshire cheese, an unripened soft cheese of the Coulommier type, and yoghurt. The yields of hard cheese from the concentrated milk were the same as those from normal whole milk. The cheeses were acceptable though the flavour was milder than that of good quality Cheddar and Cheshire cheese. Medium fat soft cheeses were made from the concentrated milk. The yield of cheese was 41 per cent greater than that made from normal whole milk and the making time was half that of the normal process. The cheeses were consumed fresh or stored in deep freeze. For making yoghurt, the usual reinforcement with skim milk powder was not necessary as the concentrated milk had a high total solids content, nor was it necessary to homogenize the mix. The yoghurt contained 21 per cent total solids and was a very acceptable product.