What is responsible for the characteristic flavour in curd?
Curd is a fermented dairy product produced by souring milk with mainly lactic starter cultures, which include Lactococcus lactis subspecies lactis, Lactococcus lactis subspecies cremoris and Lactococcus lactis subspecies lactis biovar diacetylactis. Sometimes, the starter may contain Leuconostocs. The Lactococcus lactis subspecies lactis, Lactococcus lactis subspecies cremoris are capable of fermenting lactose present in the milk into lactic acid resulting in coagulation of milk whereas the Lactococcus lactis subspecies lactis biovar diacetylactis is both lactose and citric acid fermenter. Citric acid fermentation results in the production of end products such as diacetyl, acetoin and 2,3 butylene glycol which are responsible for the characteristic desirable flavour production. Leuconostocs are purely citric acid fermenting bacteria and hence responsible for flavour production but not acid production.