Vegetable rennet is a natural enzyme that coagulates milk and separates the curds and whey when you are making cheese. Commercial vegetable rennet is often extracted from a mold called mucor miehei. Vegetable rennet is used by vegetarian cheese makers to avoid adding rennet made from animal parts. The main ingredient for homemade vegetable rennet may be growing in your backyard or a forest nearby. You can make a variety of fresh and aged cheeses using homemade vegetable rennet.
Put on rubber gloves before loading the stinging nettles into the colander. Rinse the nettles in cold water. Break off and discard any roots that are still attached.
Load the stinging nettles into a food processor and pulse the machine until they have been reduced to a green paste. You may need to load a few handfuls of the nettles at a time depending on the size of the food processor you are using.
Scoop all the vegetable matter out of the food processor into the stockpot with a spatula. Add just enough cold water to the stockpot to cover the chopped nettles. Place it on the stove over medium-high heat.
Cover the stockpot and reduce the heat to the medium-low setting once the water reaches a full boil. Slowly stir in Kosher salt with a wooden spoon until you are unable to get any salt to dissolve. Boil the nettle mash in the covered stockpot for 20 minutes.
Line the colander with a doubled-over piece of cheesecloth and lower it into a large bowl. Pour the contents of the stockpot into the colander and allow it to drain and cool for five minutes. Fold the sides of the cheesecloth over the pile of cooled nettles and press out all the remaining liquid.
Lift up the colander and discard the fully pressed stinging nettles. Use approximately half a cup of the homemade vegetable rennet for every gallon of milk you want to coagulate. Store leftover rennet in an air-tight glass or plastic container in the refrigerator for up to a week.