The development of genetically engineered chymosin has been encouraged by shortages and fluctuations in cost of rennet from calves. It's manufacturers claim that genetically engineered chymosin will end the cheese making industry's reliance on the slaughter of calves. Chymosin encoding DNA has been introduced into three different microorganisms. These are the yeast Kluyveromyces lactis, the fungus Aspergillus niger var awamori, and a strain of the bacteria Escherichia coli. There is no legal requirement for manufacturers to state whether a genetically engineered rennet has been used in the cheese making process.
Vegetarian cheeses are widely available in supermarkets and health food stores.
A wide variety of cheeses are now made with nonanimal rennet and labelled as suitable for vegetarians. No particular type of cheese is exclusively vegetarian. Soft cheeses are as likely to be non-vegetarian as hard cheeses. A list of cheeses suitable for vegetarians is available from The Vegetarian Society. The type of cheese produced depends on the milk used and the cheese making process.