Time consolidation of skim milk powder near the glass transition temperature

Time consolidation (caking) of skim milk powder was studied at 35% relative humidity and different temperatures and consolidation stresses using a ring shear tester. Unconfined yield strength developed linearly with storage time. The storage time until the powder formed hard lumps (caking time) was lower when storage temperature and consolidation pressure were increased. Even a slight increase in storage temperature near the glass transition temperature resulted in a drastic decrease of storage stability. For example, when the skim milk powder was stored 2.5 °C below the glass transition temperature, the caking time was 110 h. In contrast, an increase in storage temperature of 4 °C reduced the caking time by 80% to only 18 h. The caking time increased markedly when the storage temperature was more than 3 °C below the glass transition temperature of the skim milk powder.