Milk contains more than 90% of water, which the cheesemakers must get rid of in order to aggregate the solid matter into cheese. They do so through the curdling process. It consists in extracting the cheese matters such as proteins (casein), carbohydrates (lactose), fat (lipids), or minerals (calcium or potassium), thanks to the addition of coagulants into the milk. Animal rennet, in particular veal curd, is used for most French PDO cheeses.