A laboratory study of continuous fermentation of skim-milk for the production of sour curd cheese

Abstract

Summary The feasibility of 2-stage continuous fermentation of skim-milk to produce sour curd cheese (quarg) has been established. The first stage was a stirred pH-stat fermenter, operated at pH 5·4, 5·6, 5·8 and 6·0, in which the operating pH was maintained by inflowing fresh milk. The remaining fermentation down to pH 4·7 was carried out by a procedure which simulated a second-stage plug flow fermenter (i.e. one in which forward velocity was as constant as possible at all points of the crosssection). Skim-milk powder was dissolved to give 8, 10, 14 and 20% solids in the reconstituted milk. Maximum productivity of fermented milk solids was obtained with reconstituted milk containing 20% solids and operation of the first-stage fermenter at pH 5·4. This 2-stage continuous fermentation gave a total residence time of about 5 h, which represents a rate of production 4·8 times that obtainable in 24 h in a batch fermenter of the same fluid capacity filled once daily with the same reconstituted milk.