To make cheese you need rennet. Rennet is extracted from the inner mucosa of the fourth stomach chamber of young, un-weaned calves. It is a natural complex of enzymes produced in any mammalian stomach to help a nursing baby digest mother’s milk. In the food industry, rennet is used as a coagulant – in cheese making. There are recipes for making it from calf stomachs that you can do at home. Of course you have to have a calf and be willing to butcher it.
Rennet is available in tablet form which has a shelf life of some years if kept cool and in the dark. Liquid rennet is also available but has a short shelf life of about 1 year.
The good news is that there is a vegetable alternative. Rennet can be made from Lady Bedstraw, Stinging Nettle, and Thistle flower. Thistle cardoon is considered the best choice. Harvest the drying thistle heads before they produce white fluff. Do not use heads with fluff, they will not make rennet.
Then simmer 1 qt nettles, 1 qt water, for 10 minutes. Strain. Add to warm milk. One cup will curdle one-gallon milk. This does not work well with cow’s milk, the cheese will be bitter. It works best with goat or sheep’s milk.