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Food. % water frozen

Table 1.1 Percentage of water frozen out at various temperatures for some foods (Part of Table 1 in [1.1] and [1.2]). Table 1.1 Percentage of water frozen out at various temperatures for some foods (Part of Table 1 in [1.1] and [1.2]).
To get the water out of food without using heat, freeze-drying skips the liquid phase of water entirely. First, all the water in food is frozen solid in place. Then sublimation is used to convert the solid water into water vapor so it can be extracted without changing the shape or texture of the food. [Pg.87]

Along the line AB, solid is in equilibrium with vapor. If the pressure is decreased below the line AB, the solid will sublime. This relationship is the basis of freeze-drying foods, such as those shown in Figure 25. The food is frozen, and then a vacuum is applied. Water sublimes, which dehydrates the food very quickly. The food breaks down less when water is removed at the low temperature than when water evaporates at normal temperatures. [Pg.421]

For most substances, including water (see Fig. 10.23c), atmospheric pressure occurs somewhere between the triple-point pressure and the critical pressure, so in our ordinary experience, all three phases—gas, liquid, and solid—are observed. For a few substances, the triple-point pressure lies above P = 1 atm, and under atmospheric conditions, there is a direct transition called sublimation from solid to gas, without an intermediate liquid state. Carbon dioxide is such a substance (see Fig. 10.23b) its triple-point pressure is 5.117 atm (the triple-point temperature is —56.57°C). Solid CO2 (dry ice) sublimes directly to gaseous CO2 at atmospheric pressure. In this respect, it differs from ordinary ice, which melts before it evaporates and sublimes only at pressures below its triple-point pressure, 0.0060 atm. This fact is used in freeze-drying, a process in which foods are frozen and then put in a vacuum chamber at a pressure of less than 0.0060 atm. The ice crystals that formed on freezing then sublime, leaving a dried food that can be reconstituted by adding water. [Pg.432]

Le Meste, M., Champion, D., Roudaut, G., Contreras-Lopez, E., Blond, G., and Simatos, D. Mobility and reactivity in low moisture and frozen foods, Water... [Pg.75]

In the present chapter the effect of sucrose and hydrocolloids (xanthan gum, guar gum, and sodium alginate) on (i) Tg of the freezeconcentrated matrix (7 ), (ii) amylose and amylopectin retrogradation, and (iii) rheological behavior of the system, are analyzed in gelatinized water-starch formulations frozen at different rates and stored at — 18°C. Besides, the importance of Tg as a parameter related to texture quality of starch-sucrose-hydrocolloids-based foods during frozen storage is discussed. [Pg.313]

Probably some of tbe foods you eat have been freeze-dried. In this process, foods are frozen and the ice is removed from the food by sublimation at low pressures in a vacuum chamber. Then, the water vapor produced by sublimation is removed from the chamber by pumps or water-vapor ejectors. [Pg.353]

In practice, the rate of ice formation during freezing of foods is nearly always limited by the rate of heat removal. Even at a few degrees of undercooling, a considerable portion of the water can freeze, and this produces as much as 334 J of heat per g water frozen. Moreover, the system will soon become more or less solid, preventing convection and agitation. Hence the undercooling at the ice crystal surface is reduced to small values (often much below one kelvin). Linear crystallization rate then is rarely more than some micrometers per second this is, however, still fast compared to the rate obtained for crystallization of most substances from solution. [Pg.630]

Many foods of low water content are wholly or partly in a glassy (vitreous) state. This is of great importance for the mechanical properties and the physical and chemical stability of the food. A glassy state can also form in foods of high water content when the food is frozen, causing removal of liquid water by freeze concentration. Moreover, freezing can cause other changes that affect properties and stability. These phenomena are the subject of this chapter. [Pg.669]

FIGURE 16.10 Examples of the proportion of water frozen as a function of temperature in some foods. [Pg.690]

The machine runs the compressors to lower the temperature in the chamber. The food is frozen solid, which separates the water from everything around it, on a molecular level, even though the water is still present. [Pg.8]

Starch monophosphates are quite useful in foods because of their superior freeze—thaw stabiUty. As thickeners in frozen gravy and frozen cream pie preparations, they are preferred to other starches. A pregelatinized starch phosphate has been developed (131) which is dispersible in cold water, for use in instant dessert powders and icings and nonfood uses such as core binders for metal molds, in papermaking to improve fold strength and surface characteristics, as a textile size, in aluminum refining, and as a detergent builder. [Pg.346]

For this purpose, as well as for many other food uses, the vegetable gums, as a group, are often preferred to the starches, especially those of the cereal variety, because they do not tend to retrograde at low temperatures, as do these starches. Consequently, with the increasing popularity of frozen food products, the water-soluble gums are in greater demand. [Pg.7]

Riedel, L. Enthalpie-water content diagram for lean beef (also valid for other meats with fat content below 4 %). Recommendations for the processing and handling of frozen foods, p. 28 and 29. International Institute of Refrigeration 75 Paris 17e, France, 2. ed 1972... [Pg.118]

Duckworth, R. B. Differential thermal analysis of frozen food systems. I. The determination of unfreezable water. Joum. Food Technol. 6, p. 317-327, 1971... [Pg.118]


See other pages where Food. % water frozen is mentioned: [Pg.234]    [Pg.83]    [Pg.224]    [Pg.767]    [Pg.25]    [Pg.407]    [Pg.304]    [Pg.1332]    [Pg.275]    [Pg.1332]    [Pg.435]    [Pg.337]    [Pg.500]    [Pg.156]    [Pg.295]    [Pg.517]    [Pg.269]    [Pg.449]    [Pg.459]    [Pg.459]    [Pg.459]    [Pg.301]    [Pg.25]    [Pg.143]    [Pg.309]    [Pg.450]    [Pg.46]    [Pg.49]    [Pg.52]    [Pg.954]   
See also in sourсe #XX -- [ Pg.3 ]




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