Traditionally, semihard cheese is made in Scandinavia from bovine milk using calf rennet and mesophilic DL-starter (see Sec. III below). The milk is commonly collected from two to four meals, and deep cold storage is used at the farms as well as at the dairies. This treatment of the cheese milk decreases the coagulation ability that mainly is restored by pasteurization (73°C/15 sec) and sometimes, depending on season and cheese variety, also an addition of CaCl2 is needed. Other bacteria than the starter bacteria may be added during cheese production. These include PAB to Jarlsberg, Greve, Magre; and Svenbo; Lactobacillus helveticus to low-fat cheese; and Brevibacterium linens, which may be sprayed on the surfaces of some Danish cheeses (Table 1).

Calf rennet is commonly used and has not easily been replaced by other coagulants. The rennet is active during the primary casein breakdown during cheese ripening, and the characteristic physical properties of the ripened cheeses are dependent on its specific activity. The main coagulating enzyme in calf rennet is chymosin. Depending on the age of the calf and on its feedstuff, the calf rennet also contains different amounts of of the proteolytic enzymes bovine pepsin and gastricsin (1). Chymosin is an aspartic proteinase, which has its activity optimum at low pH (pH 5.0 with as1-casein as substrate) and a preference to cleave Phe-X and Leu-X peptide bonds (2,3). Rennet-mediated milk coagulation begins with a specific cleavage of the n-casein bond Phe105-Met106 to release the hydrophilic glucoma-cropeptide, which is lost in the whey. Structural rearrangement of the remaining hydro-phobic para-casein effect coagulation and later syneresis when the whey is expelled from the cheese grains.

The temperature/time periods used during production of the semihard cheeses differ among the cheese varieties within certain limits as exemplified in Fig. 1 for a cheese in the lower part of the moisture content interval (Table 1). Coagulation temperature may be increased by one or two degrees for low-fat cheeses and stirring temperatures may be as high as 35°C. Lower production temperatures and shorter holding times are used to obtain the higher moisture content of some semihard cheese varieties. A variation of temperature/time periods are used to obtain different moisture as well as mineral contents, but they also influence the starter bacteria and cause variations in their further development and contribution to cheese ripening.

Figure 1 Typical pattern of time/temperature intervals for the production of semihard cheese in the lower moisture content interval, such as Herrgârd cheese (Table 1).

Traditionally some Scandinavian cheese varities were made with higher cooking temperature than today, and specific characteristics of Herrgard still depend on the combination of using a mesophilic starter culture in combination with longer time at somewhat higher cooking temperatures than those cultures commonly are used for. This technique using mesophilic starters and very long holding times is further developed for production of the hard Swedish cheese Vasterbotten. This cheese has a characteristic hard texture that differs from most other hard cheeses that are made with thermophilic starter and higher cooking temperatures.

Semihard cheese with round eyes is prepressed under whey, whereas the whey is separated from the grains before the pressing of cheese with an open texture. Acidification takes place in cheese mainly after molding during the first 24 hr while the lactose is almost completely converted into lactic acid. To prevent pH from decreasing too much, parts of the whey may be removed and water is added to the vat. The minimum pH of the semihard cheese varieties is commonly around pH 5.1-5.3 and depends on cheese variety. DL-starter bacteria in semihard cheese have preferentially used up the citrate after one or two weeks, while CO2 is produced leading to the eye formation.

The semihard cheeses are brine salted and kept within a NaCl solution of about 2022% for different periods of time depending on cheese variety. Small-sized, low-fat, high-moisture cheeses may be salted for as short a time as 8 hr. dryer cheeses may be kept in the brine for up to 3 days to achieve a salt content of about 1-2% in cheese. The mild, high-moisture, and smear surface-ripened cheese varieties need only a couple of weeks of ripening, whereas several of the other semihard cheese varieties are ripened from 3 months and up, to a year or more.

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