Ricotta

Ricotta is an Italian whey cheese made from sheep, cow, goat, or Italian water buffalo milk whey left over from the production of other cheeses. Like other whey cheeses, it is made by coagulating the proteins that remain after the casein has been used to make cheese, notably albumin and globulin. Ricotta (lit. 'recooked' or 'refined') protein can be harvested if the whey is first allowed to become more acidic by additional fermentation (by letting it sit for 12–24 hours at room temperature). Then the acidified whey is heated to near boiling. The combination of low pH and high temperature denatures the protein and causes it to flocculate, forming a fine curd. Once cooled, it is separated by passing the liquid through a fine cloth, leaving the curd behind. Ricotta curds are creamy white in appearance, and slightly sweet in taste. The fat content varies depending on the milk used. In this form, it is somewhat similar in texture to some fresh cheese variants, though considerably lighter. It is highly perishable. However, ricotta is also made in aged varieties which are preservable for much longer.

Source: Wikipedia