Influence of refrigeration on evaporative weight loss from meat 87 water is present on the surface of a carcass and the pm can be assumed to equal that of saturated vapour at the same temperature as the surface. As he surface cools, water evaporates and this assumption only remains true if the rate of diffusion is high enough to maintain free water at the surface nvestigations in South Africa(Hodgson, 1970) reported that during chill ng of a beef side only a part of the surface remained saturated throughout the operation. After flaying, the surface apparently dried, reaching maximum dehydration after ca 10h when only 70% of the surface was wet Diffusion then gradually restored free water to the surface until, after 20h under the test conditions. 90% of the surface was wet There was no defi- nition of wetin the paper but we interpret the statement to mean that after 10h the rate of evaporative loss was 70% of that from a saturated surface at the same temperature. No other published work relating to carcasses has been located, but Australian experiments(Lovett et aL., 1976) on small samples produced a similar pattern. There is a short initial phase, when the rate of evaporation is the same as that from free water This is followed by a decreased rate of evaporation below the value expected from a water surface and a final phase where the surface is pro- gressively re owever Daudin and Kuitche(1995), predicted weight loss from pork carcasses assuming a fully wetted surface to a stated accu racy of 0. 1% A simple examination of Ficks law gives an indication of the problem in calculating the rate at which diffusion can occur through meat. It states Md=KAδC [52] Where Ma is the rate diffusion of water, K is the diffusion coefficient and SC is the concentration gradient Meat is a non-homogeneous material consisting of fat, lean and bone and even these three elements are heterogeneous within themselves. Lean com nercially the most important component, is the muscle tissue of the live animal and consists of fibre bundles and connective tissue. The fibres have a preferred orientation, and diffusion coefficients and concentration gradi- ents vary with this orientation and the presence of barriers of different permeability within and between muscles. The rate of diffusion cannot herefore be predicted with any great degree of accuracy 5.2 Weight loss in practice In this section the unit operations present in a meat distribution chain, chill- ing, chilled storage and display, freezing and frozen storage, are considered from the point of view of weight loss. Since the majority of the loss tends to occur during chilling, it is given greater consideration than the other processes.water is present on the surface of a carcass and the Pm can be assumed to equal that of saturated vapour at the same temperature as the surface. As the surface cools, water evaporates and this assumption only remains true if the rate of diffusion is high enough to maintain free water at the surface. Investigations in South Africa (Hodgson, 1970) reported that during chill￾ing of a beef side only a part of the surface remained saturated throughout the operation. After flaying, the surface apparently dried, reaching maximum dehydration after ca. 10 h when only 70% of the surface was wet. Diffusion then gradually restored free water to the surface until, after 20 h under the test conditions, 90% of the surface was wet. There was no defi- nition of ‘wet’ in the paper but we interpret the statement to mean that after 10 h the rate of evaporative loss was 70% of that from a saturated surface at the same temperature. No other published work relating to carcasses has been located, but Australian experiments (Lovett et al., 1976) on small samples produced a similar pattern. There is a short initial phase, when the rate of evaporation is the same as that from free water. This is followed by a decreased rate of evaporation below the value expected from a water surface and a final phase where the surface is pro￾gressively rewetted. However, Daudin and Kuitche (1995), predicted weight loss from pork carcasses assuming a fully wetted surface to a stated accu￾racy of 0.1%. A simple examination of Fick’s law gives an indication of the problems in calculating the rate at which diffusion can occur through meat. It states that: [5.2] Where Md is the rate diffusion of water, K is the diffusion coefficient and dC is the concentration gradient. Meat is a non-homogeneous material consisting of fat, lean and bone and even these three elements are heterogeneous within themselves. Lean, com￾mercially the most important component, is the muscle tissue of the live animal and consists of fibre bundles and connective tissue. The fibres have a preferred orientation, and diffusion coefficients and concentration gradi￾ents vary with this orientation and the presence of barriers of different permeability within and between muscles. The rate of diffusion cannot therefore be predicted with any great degree of accuracy. 5.2 Weight loss in practice In this section the unit operations present in a meat distribution chain, chill￾ing, chilled storage and display, freezing and frozen storage, are considered from the point of view of weight loss. Since the majority of the loss tends to occur during chilling, it is given greater consideration than the other processes. M KA C d = d Influence of refrigeration on evaporative weight loss from meat 87