Ricotta is a "by-product cheese" (gross), made from the whey which is left over from other cheeses. "Ricotta" literally means "
recooked." Leftover
whey from hard cheeses is heated and combined with a little
fresh milk. The result is a soft white
curd cheese with a rather solid, kinda
granular consistency. 20% fat.
Commercially-produced ricotta is made from cow's milk, but in rural areas sheep's or goat's milk is sometimes used.
The American Heart Association suggests using ricotta as a low-fat substitute for sour cream, but come on.
http://www.fratelli-bosco.co.uk/Cheeses/Cheeses_f.htm