Rennet is added to milk to make cheese. The rennet breaks down the protein in the milk that keeps it in liquid form and causes it to curdle. Most cheese is made from rennet harvested from the stomachs of cows. Many vegetarians prefer to use vegetable rennet in their cheese. Vegetable rennet is fairly easy to harvest from the right source. One of the more common sources of vegetable rennet, which is commonly used in Scotland, is the stinging nettle.
Add 1 lb. of stinging nettles to a large pot. Add enough water to just cover the nettles. Boil for 20 to 30 minutes.
Pour the mixture through a wire mesh strainer and into a large bowl.
Stir in salt until no more will dissolve in the mixture. Stop when you begin to see salt collect at the bottom of the bowl.
Add 1/2 cup of homemade nettle rennet per gallon of milk.