Sour milk cheese or acid-set cheese is a cheese that has been curdled (coagulated) by natural souring or by the addition of lactic acid bacteria, such as traditional curd cheese or cottage cheese. Sour milk cheese does not use rennet for coagulation.
Sour milk cheese generally ripens for no more than two weeks in comparative warmth. 100 litres of milk yield about 8 to 9 kilograms of sour milk cheese, which contains less than 10% fat and up to 37% protein. Most sour milk cheeses are white mould cheeses or red mould cheeses, and many are flavoured with caraway (e.g. traditional Latvian Jāņi cheese).
In Germany the term Sauermilchkäse is usually applied to ripened acid-set cheeses only, but not to fresh cheeses. The various types of ripened sour milk cheese include: