a In cheeses like Danbo with citrate-fermenting starter bacteria, the citrate is converted within 1 to 2 weeks to volatile compounds such as carbon dioxide, diacetyl, and acetic acid.
b Under conditions of storage and ripening, the moisture content of the cheese (and the weight of the cheese) will decrease because of evaporation, unless the cheese is packed in synthetic film or covered with cheese wax.
Unless the cheese is made shortly after milking, the milk should be kept cool till start of cheese production in order to prevent excessive growth of bacteria. During storage at low temperatures, the rennetability may be slightly reduced.
Cheese is often made of raw milk, and it is a common assumption that cheese made of raw milk of good quality can be more rich in flavor. Some pathogenic bacteria, however, such as Mycobacterium tuberculosis and Listeria monocytogenes, can survive in cheese for months, and in many countries pasteurization of milk for cheese is mandatory. Pasteurization at 72°C for 15 sec typically kills about 99% of the bacteria of the raw milk. Bacterial spores, however, will not be killed. About 95% of milk lipase will be inactivated at 72°C for 15 sec, a fact that may help to explain a part of the assumed richer flavor of raw milk cheese. Most of the whey proteins remain unchanged by pasteurization at 72°C for 15 sec, but at slightly more intensive heat treatment, the whey proteins begin to denature. Denatured whey proteins precipitate together with the caseins by the action of rennet, or by acid at pH 4.6, yielding a higher total retention of the proteins. For most cheeses, however, a heating greater than 72 °C for 15 sec is normally not applied, because more intensive treatment implies certain drawbacks: slower renneting of the milk and a weaker coagulum; inactivation of the enzyme xanthine oxidase, which catalyzes a reduction of added nitrate to nitrite; and slower development of cheese flavor and texture during ripening.
For some types of cheese (e.g., Danablu, and Feta produced by ultrafiltration), homoge-nization may be applied in order to whiten the cream and to increase the water-binding capacity of the cheese curd. Homogenization also increases the lipolysis of the fat, provided active lipase is present.
These processes are widely used in the production of cheese types liable to damaging fermentation by the spore-forming bacteria Clostridium tyrobutyricum (e.g., Emmental and Gouda/Danbo cheeses). With bactofugation a large part of the bacteria, and more than 90% of the spores, can be removed from the milk. With microfiltration more than 99.9% of all bacteria and spores can be removed from the skim milk part of the milk. The cream of the milk then has to be heat-treated separately because the fat globules otherwise would block up the filter membranes.
In both processes, some of the bacterial spores follow the cream, adhering to fat globules. In order to produce cheese with a low number of Clostridium tyrobutyricum spores, the cream can be pasteurized at about 120°C for a few seconds, prior to mixing cream with skim milk from bactofugation or with permeate from microfiltration. Both the retentate from microfiltration and the bactofugate from bactofugation contain most of the spores from the milk and also a part of the casein, and for utilization of this casein, the retentate/ bactofugate can be mixed with the cream before the heat treatment.
By ultrafiltration, milk can be separated into a retentate in which fat, bacteria, casein micelles, and whey proteins are concentrated and a permeate containing water and lactose. Salts linked to the caseins in the micelles (most of the calcium and phosphate and a part of the citrate) will be concentrated in the retentate, whereas other salts will follow the water into the permeate. Ultrafiltration thus resembles the natural filtration process in the curd grains in traditional cheesemaking, in which the casein network acts as a filter—with the exception that the ultrafiltration membranes also retain the whey proteins. Concentrating milk for cheese by ultrafiltration is utilized in large scale of production of UF-Feta cheese, where the retentate, with about 40% total solids after addition of starter culture and rennet, can be cast directly into tins. Because the whey proteins are retained in the retentate, the yield of cheese by ultrafiltration is higher than in conventional cheesemaking. By ultrafiltrating of a part of the milk, the protein content of the cheese milk can be increased and standardized for conventional cheese production.
Cheeses are usually classified by percent fat in dry matter (FDM) according to legal standards. The fat content of the cheese milk has to be adjusted according to the percent FDM desired and according to the protein content of the milk.
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