Influence of fermentation conditions on rheological properties and serum separation of ayran

Effects of culture type (ropy and nonropy), fermentation temperature (40 and 43C) and final pH (4.3 and 4.6) on the rheological properties and serum separation of ayran, a salt-containing yoghurt drink produced in Turkey, were investigated. Highfermentation temperature yielded high apparent viscosity, high consistency coefficient, low flow behaviour index and high thixotropy in ayran. Effect of final pH on the rheological properties depended on the fermentation temperature and type of culture used. Low fermentation temperature and high final pH yielded ayran with low consistency coefficient, high flow behaviour index and low thixotropy. Excessive serum separation was observed in all ayran samples but samples produced at high fermentation temperature and low final pH exhibited less serum separation compared to other samples. Ropy culture did not increase apparent viscosity and reduce serum separation in ayran at any fermentation temperature and final pH combination compared to nonropy culture. Temperature of 43C and final pH of 4.3 at fermentation are recommended for the manufacture of ayran to increase viscosity and to reduce serum separation.