Cheese cultures are strains of bacteria (the good kind) that are isolated by culture makers (yup, there are such people) so they can keep making the best cheeses. When added to milk, cheese cultures consume the lactose (or milk sugar) and turn it into lactic acid, which helps the vegetable rennet (proteins with coagulating properties) turn the milk into a solid block of cheese. In simpler terms, magic. Magic makes cheese happen.
Aren't we all turophiles?
Turophile is the official name of a cheese connoisseur. Try sharing that fun fact at your next party—you may sound more interesting, if not a bit cheesy.