Abstract
SUMMARY: The heat stability of skim-milk powder varied throughout the season, but was highest during the period April–August. Addition of urea increased heat coagulation times during March–August, but the extent of increase was dependent upon urea addition either before or after preheating for 30 min at 90 °C during manufacture. During March–June, higher heat stabilities were recorded when urea was added after preheating, while in July–August urea added before preheating was more effective. Partial ultrafiltration before dehydration decreased the heat stability of reconstituted milks due to a loss of natural urea in the permeate together with a disruption in the salt balance.