Cheese in the categorization of these cheeses is their age. Fresh cheeses without additional preservatives can spoil in a matter of days. Content (double cream, goat, ewe and water buffalo) Some cheeses are categorized by the source of the milk used to produce them or by the added fat content of the milk from which they are produced. While most of the world's commercially available cheese is made from cows' milk, many parts of the world also produce cheese from goats and sheep. Some cheeses are described by their fat content. Double cream cheeses are soft cheeses of cows' milk enriched
Egyptian cheese or close to it; there was an old dry cheese; and there was a medium one in between." The first would have been unripened cheese made locally from sour milk, which may or may not have been salted. The old dry cheeses would have often been imported, and were cheeses ripened by rennet enzymes or bacteria. The nature of the "medium" cheese is less certain, and may have referred to preserved fresh cheeses, evaporated milk or cheese similar to Indian paneer, where the addition of vegetable juices makes the milk coagulate. Medieval Egyptian cheese mostly used buffalo or cows' milk,