I met Jon Clark at a recent cheese class where he was a student. Jon is currently teaching English in Hungary. Though he is really interested in making cheese, he does not have the luxury of being able to order ingredients over the internet and have them arrive in a timely or economical fashion.
We discussed that it is possible to harvest your own rennet, and I forwarded him a link to another obsessed cheesemaker, David B. Fankhauser. Dr. Fankhauser shows his attempt to create his own rennet from the stomach of a suckling kid (the goat kind). I thought if Jon were really desperate, this was something that he could try. If seeing where your food comes from does not disturb you, check it out here.
Jon replied and told me he had coincidentally just seen that very page in a recent posting to the blog Serious Eats. In this entry Jake Lahne discusses the use of the Cardoon Thistle as a cheesemaking coagulant.
I have read in American Farmstead Cheese that thistle was used in historic cheesemaking when animal rennet was not available or not desired. Jewish cheesemakers used thistle to create a kosher cheese (avoiding mixing meat and milk). Some cheeses are still made today using this process: Torta la Serena, Torta del Casar, and Serra da Estrela are examples.
I am very curious about trying to use Cardoon as a coagulant. My favorite seed company carries it, so I will try planting some this year. Stay tuned for results this summer/fall.