The nature of the structural attributes of ice cream determines physical properties like hardness and melting rate. Structural attributes include properties of the air phase (overrun and air cell size distribution), ice phase (ice phase volume and ice-crystal size distribution), fat phase (total fat content, fat-globule size distribution and extent of fat destabilization) and the continuous phase (viscosity and gel formation). These structural elements are developed during manufacture and storage of ice cream through control of the formulation and process conditions. An understanding of the effects of these structural attributes is needed to better control the quality of ice cream.

Air is an important component in ice cream, affecting both physical properties and storage stability. The objective of this study was to measure the effects of air incorporation in ice cream, at overrun levels of 80%, 100% and 120%, on the growth of air cells and ice crystals, as well as on the hardness and melt-down rate of the product. Ice creams with different overruns were stored either in bulk containers (at −10°C with normal refrigeration cycling) or on microscope slides (at −6°C, −10°C or −20°C) for analysis. In bulk storage, mean air cell size initially increased during hardening, decreased during the early stages of storage and ultimately increased to larger sizes at longer (up to 3 months) storage times. Initial air cell size was smaller in ice creams with higher overrun, potentially due to the higher shear stresses during manufacture. Ice creams with lower overruns (80%) were harder than those made with 120% overrun but melted more rapidly. For samples stored on the microscope slide, lower storage temperature (−20°C) limited the mobility and solubility of air cells within the serum phase so that disproportionation was inhibited and primarily coalescence occurred for air cells in close proximity. At high storage temperature (−6°C or −10°C), disproportionation and coalescence were enhanced due to the higher mobility of the serum phase. Higher overrun led to slightly more stable air cells during storage.