It's commonly known that cheese is made from animal rennet, which comes from the stomach linings of calves. But what most people don't know is that cheese can be made from plant rennet, and that the purple thistle flower is one of those plants that can cause heated milk to coagulate and form cheese. Cheeses produced this way are classified as vegetarian cheeses. If you've been battling the weedy purple thistle in your yard for years, you can now put the pesky little plant to work for you.
Pick the thistle flower head when it has turned brown. Harvest it before the plant can start producing thistle down. If thistle down is evident, it means it's too late--the flower head is too mature and therefore unusable. Be sure to collect enough dried flower heads to last for the year.
Dry the thistle flower heads well before storing them in a clean dry jar with a lid.
Put a couple dried thistle heads in a mortar and start grinding them into a fine powder. Make sure they are well crushed.
Repeat Step 2 until there are 5 tsp. of powder. Put it in a bowl and pour warm water over the ground thistle flower powder. Let it soak for a good five to 10 minutes.
Watch for the liquid to turn a dark, concentrated brown color.
Pour the liquid through a strainer to separate the plant material from the liquid. This is thistle flower rennet.
Add to a gallon of heated milk and wait for curdling to begin.