The influence of milk dry matter (DM) content (8.20%, 9.27% and 10.28%) and applied heat treatments (untreated milk and milk heat-treated at 90°C/10’) on the viscosity of set-style yogurt and acid casein gel gained by acidification with GDL (glucono-d-lactone) has been investigated. Viscosity was measured during the time of 3 minutes at constant speed of spindle rotation of 20 rpm. The results have shown that yogurt samples produced from untreated milk had higher viscosity values than samples produced from heat-treated milk.

Reconstituted skim milk with 8.01% DM was standardized with 3% skim milk powder and with 3% demineralized whey powder (DWP), respectively. Gained milk samples are named as 8%, 11% and 8%+3%DWP. All samples were heat treated at 85ºC/10 min, 90ºC/10 min and 95ºC/10 min, respectively. Untreated milk was used as control. Milk samples were coagulated by glucono-d-lactone (GDL) at the temperature of 45ºC until pH 4.60 was reached.

Skim milk powder was reconstituted to obtain milk A (with 8.01% TS). Milk A was standardized with 3% of skim milk powder and 3% of demineralized whey powder (DWP), respectively, to obtain milk B (with 11.15% TS) and milk C (with 11.10% TS). Milk samples were heat treated at 85ºC/10 min, 90ºC/10 min and 95ºC/10 min, respectively. Untreated milk was used as control.

Skim milk with 9.15% DM was heat treated at 85°C/10 min, 90°C/10 min and 95°C/10 min, respectively. Untreated milk was used as control. Milk samples were coagulated by glucono-δ-lactone (GDL) at the temperature of 45°C until pH 4.60 was reached. Untreated milk had the longest time of acidification. Nitrogen matter content in sera obtained from untreated milk was 79.40 mg%.