Air cell microstructuring in a high viscous ice cream matrix

Ice cream is a complex multiphase system consisting of ice crystals, air cells and fat globules embedded in a high viscous freeze concentrated matrix phase. The microstructure of these constituents has significant impact on the consumer quality characteristics and its specific manipulation is of great interest. While in the frozen state the structure is dominated by the ice crystals after thawing the foam characteristics become important. Ice cream foam stability is correlated to the sensed creaminess and can be improved with smaller air cells and reduced coalescence. In contrast to the common approach addressing this goal by changed recipes this contribution proposes an additional process step which allows efficient dispersion of the air cells by high shear forces. Disruption of air cells by shear is efficiently done at high matrix viscosities, which are directly related to the amount of frozen water and therefore the temperature. Conventionally scraped surface heat exchangers (freezers) are used for whipping and freezing of an ice cream premix. With outlet temperature of -5 to -8 C these devices operate at relatively low ice cream viscosities. Here the ice cream is processed in a low temperature extruder (LTE) after a classic freezer which cools it further to below -12 degrees C. This way shear forces exceeding those in the conventional system by 2-3 orders of magnitude can he applied, The maximum air cell diameter x(90.3) is reduced from 52 to 19 mu m. Beside the air structures the extrusion process induces also changes in the fat structures. High shear forces are also able to form an optimized network of agglomerated fat globules, which further stabilize.,, the foam, These structural changes have a significant impact on the foam related quality characteristics of ice cream its is proven by measurements, of the rheological behaviour during thawing and melt down tests. (c) 2004 Elsevier B.V. All rights reserved.