Survey of lactic acid bacteria isolated during the advanced stages of the ripening of Parmigiano Reggiano cheese

Abstract

Parmigiano Reggiano is a hard, cooked cheese produced in specific areas of Northern Italy. The raw material is obtained by mixing the partly skimmed evening milk and whole morning milk. The mixture is then heated to 22°C, and natural whey starter is added at 28–30 g/l after 1–2 min, bringing the pH of the mixture to 6·2–6·3. After coagulation, which takes ∼15 min and occurs at 32–33°C owing to the addition of calf rennet powder, the curd is broken up for 2–4 min, cut into fragments and cooked at a temperature raised gradually to 42–44°C and then more quickly to 55–56°C over 10–15 min. The curd is left undisturbed, covered by the whey, for 40–60 min, then removed and placed inside a circular wooden mould. The cheese is held at ∼20°C for 3 d during which it is turned at frequent intervals to facilitate complete whey drainage. The cheese, which now has its typical shape and size, is then salted by immersion in brine (260–280 g NaCl/l at 16–17°C) for 20–24 d. During this period the cheese absorbs 15–18 g NaCl/kg and its weight decreases by 4%. During the subsequent period of ripening (12–24 months) in store rooms at 16–18°C and 85% moisture, the cheese is frequently turned. At the end of ripening the cheese is cylindrical in shape, with a slightly convex side, 0·22–0·24 m high, 0·40–0·45 m diam. weighs 35–36 kg, has 320–330 g fat/kg dry matter and a minutely granulated internal structure with small holes formed by the activity of some heterofermentative lactic acid bacteria.