THE EFFECT OF ELEVATED MILK SOLIDS AND INCUBATION-TEMPERATURE ON THE PHYSICAL-PROPERTIES OF NATURAL YOGURT

Liquid skimmed milk (8.5% total solids (TS)) concentrated to 16% TS by ultra-filtration gave better quality yoghurt with respect to gel stre ngth (set yoghurt) or viscosity (stirred yoghurt) than milk fortified to the same extent with skim-milk powder or reduced in volume by vacuu m evaporation to 16% TS. This contrast was confirmed both by technique s destructive to the gel structure (penetrometer/set yoghurt and visco meter/stirred yoghurt) and by nondestructive dynamic rheometry. Althou gh the precise reasons for the beneficial effects of ultra-filtration were not explored, the findings could have important implications for small-scale producers wishing to invest in process plant to avoid the use of expensive skim-milk powder.