Propionic Culture is used to produce 'holey' hard cheeses such as Emmental and Gruyere. The mould will cause the holes to form during the early ripening process. For best overall effect the cheese should not be too acid: a pH of 5.2-5.4 is ideal. Wash the curd with lots of water to remove acidity. Brine or saltpetre solutions should not be used at any stage. For the first week the cheese should be stored in the ripening area at 23C. Each sachet provides enough culture for 2500 litres of milk.