Frozen foams

Ice cream consists of ca. 40% air-frozen foam. The continuous phase in foam consists of sugars, proteins, and emulsifiers. A typical ice cream contains... 

Ice cream is a partially frozen foam that is also an emulsion and a suspension, containing many components including proteins, fat, water, and air. A typical ice cream mix might contain milk fat (10-16%), milk solids-not-fat2 (9-12%), sugars (9-12%), corn syrup solids (4-6%), stabilizers and emulsifiers (0-0.5%), and water [430,811,815], When prepared, ice cream may have an overrun (Section 13.3) of 70-100% (that is, it will contain 40-50 volume percent air) [811], see Table 13.2. Due to the partial freezing, ice cream also contains dispersed ice particles. At -11 °C ice cream has a viscosity of about 109 mPa s [215]. 

The number (or size) of bubbles observed in a frontal unit surface area from a cut layer of the frozen foam differs from the bubble number in the volume for two reasons. The first one is related to the fact that small bubbles (because of their small sizes) very often do not fall into the cut surface [8,41 ]. That is why the number of bubbles in the cut surface Ns is smaller than the number of bubbles Nf in a layer from the foam volume with height equal to two average bubble radius. The relation between bubble distribution functions by the radius R in the foam volume and in the frontal layer is given by de Vries [8]... 

The properties of a low expansion ratio foam are controlled mainly by changing the rate of the kinetic processes running in it. To decelerate the hydrodynamic processes in order to preserve its structure for a longer time (for instance, in the formation of polymer or frozen foams), the following measures can be recommended i) to use a foam generation mode that allows producing a foam of a uniform expansion ratio such are the stream type generators and some mechanical devices that mix the solutions ii) to produce a foam of maximum dispersity... 

In order to design a composition of foaming agents and to select the optimum technological parameters for frozen foam production and deposition on soils, the stability of foams from various foaming agents has been studied [115]. Focused were the internal foam... 

Coefficient of water vapour transport in a frozen foam of various compositions... 

The formation and preservation of the uniform cell structure of either the solid polymer or frozen foam depend on the properties of the initial foam, i.e. on its expansion ratio and stability. On the one hand, the former two processes are determined mainly by the rates of drainage and internal foam collapse. On the other hand, however, they are affected by the rate of polymerisation and the increase in strength of the foam material. That is why optimisation of the processing properties of polymer foams can be achieved by decreasing both the rate of microsyneresis and drainage, and the rate of internal foam collapse. Along with that precise control of the rate of solidification, reduction of the water content and introduction of plastifiers are needed. 

A relatively simple method for evaluating foam stability consists of flash-freezing the foam in liquid nitrogen, slicing the frozen foam and then observing the cells under the microscope. Image analysis and optical probe... 

Ice cream is a physically complex, partially frozen foam mixture of water, cream, and sugar that consists of about 50% air by volume. Ice crystals and air bubbles typically measure 20-50 pm and 50-100 pm, respectively. 

The CCD images taken at various temperatures (Fig. 6a-c) show that at higher temperatures, the initial expansion rate was significantly high. However, due to accelerated gas at this high temperature, the final diameter of the extruded foam was small. As the temperature decreased, the initial expansion rate..decreased because of the lower diffusivity, whereas the final diameter of the extruded foams increased due to less amount of gas loss. An optimum temperature existed in order to achieve the maximum diameter of the extrudate, which seemed to be correspondent to the final maximum expansion ratio of PP foam. When the temperature was decreased further, the diameter of foam extrudate reduced again due to the crystallization (i.e., frozen foam skin). 

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