i am in the middle of making mozzarella (and failing). my recipe says to knead it until it is smooth, shiny, and stretchy and that it should only take a few minutes. but i have been working on it for at least 15-20 minutes and it is the texture of ricotta cheese, ie: very tiny curds, soft and crumbly. not at all smooth, shiny or stretchy. what have i done wrong and can i fix it?