Pithkia - rennet

Πυτία. 
Dried and salted stomach lining of a newborn sheep, goat or pig, which had not eaten grass yet and was still being fed with milk (Rizopoulou-Igoumenidou, 2008). This is also noted by Georgios Loukas and Ioannis Erotokritos, in their Glossaries (Kypri 1979 [2002²], entry πυδκιά και μαγιά,η, 414; Kypri 1989, entry πυδκιά,η, 156). Pythkia is "dried stomach lining of a newborn animal, which contains enzymes that help milk to curdle and become cheese, halloumi, etc." (Petrou-Poeitou 2013, entry πυδκιά,123).

It is an enzyme secreted by the stomach lining. It belongs to the proteases (enzymes that hydrolyze albumin). In the acidic environment of the stomach, rennet causes milk to coagulate and, together with pepsin, causes the breakdown of casein. When it acts on the casein of milk, it forms paracasein, which in the presence of calcium ions gives calcium paracaseinate. This is insoluble and it settles and drags along a certain number of lipospheres and so cheese is formed. This is the reason for using rennet in cheese making.

Pithkia is found in large amounts in the gastric fluid of young children and animals, especially in the fourth stomach of ruminants. Adult individuals have only traces of rennet. This explains why milk casein is more easily digested in babies and young children than in adults.

A coagulant enzyme that is found in the gastric fluid of calves and is used in the coagulation of milk for the production of cheese (Babiniotis 2005, entry πυτιά,η, pp.1522-1523).