Stability of air cells in ice cream during hardening and storage

Air cells in ice cream were monitored, with either a light microscope technique or cryo-SEM, during hardening and storage at different temperatures. Ice cream samples were: (1) held at −6.0 or −15.0 °C on a microscope stage for observation of air cells; (2) hardened at different rates to −28 °C; and (3) stored at −15 °C for four months. At temperatures above about −18 °C, three main mechanisms of air cell instability (disproportionation, coalescence and drainage) were observed. As temperature of storage decreased, the rate of change in air cells decreased. Disproportionation of air cells was inhibited by addition of emulsifiers or stabilizers, although the mechanisms for this inhibition were different. During long-term storage of ice cream, interconnection between air cells led to severe channeling. However, cryo-SEM was needed to observe this channeling behavior since the optical microscopy technique did not preserve the true structures of the air cells in ice cream under these conditions.