Combined effects of process parameters and composition on foaming of dairy emulsions at low temperature in an agitated column

The pre-aeration of dairy emulsions of composition similar to an ice cream mix was investigated under steady state conditions using a narrow annular gap unit equipped with a cross-blade impeller which occupies 7% the volume of the column. The combined influence of composition of mix and process parameters on unfrozen aerated emulsions was studied using two milk protein sources (skim milk and whey respectively), two commercial grade fats (differing by the amount of solid fat) and two types of commercial emulsifier blends (saturated and unsaturated mono- and di-glycerides). Foams were characterised in terms of overrun, bubble size distribution, rheological properties and fat destabilisation. Experimental results showed that stabilised unfrozen foams could be produced at a temperature higher than the freezing point, with an air cell size similar to that observed at the exit of a continuous ice cream freezer. Smaller bubbles were obtained with unsaturated emulsifiers and the highest level of stability was achieved with unsaturated emulsifiers combined with commercial fats characterised by the lowest solid fat content. A simple analysis based on dimensionless Weber and Reynolds numbers was developed to correlate the mean bubble diameter to process parameters and emulsion properties. Results differed widely as a function of emulsifiers.