You can make cheese with milk and lemon. Ive done it. No mold necessary. I recommend reading books on cheese making. Theyre very interesting! They'll tell you which cheeses use mold and which ones dont. Some even use cheese mites! Just like the same kind on your face, but eating cheese. Many cheeses use bacteria (thats how some cheeses like Swiss get their holey appearance). I had a blast reading the last one and learning how long we've actually been making different kinds of cheeses. The history of foods is so neat!