92 Meat refrigeration 上 目-20° C forced ventilation口-16° free convection口-26° C free convection Fig 5.1 Weight loss from unwrapped hams in frozen storage(source: Malton an More meat is now wrapped in impervious material before freezing, but despite popular belief to the contrary, such packaging does not completely eliminate weight loss. Evaporative losses from polyethylene-wrapped carcass meat frozen at -30C are negligible, but losses of up to 0.5%have been recorded at-10oC The slower freezing time allowed water to migrate from the meat to the inner surface of the polyethylene Oss o published information has been located of the effect of RH on weight loss during frozen storage pre bly because of the difficulty of measur- ng RH at temperatures below 0C. Figure 5.1 shows clearly the detrimen tal effect of both air movement and high storage temperatures on weight loss. Although weight losses per day in frozen storage are small, storage imes can be long with consequent overall losses as high as 10%(Roussel and Sarrazin, 1970). The importance of temperature control as well actual temperature is supported by French experiments( Gac et aL., 1970) Lean beef stored in cartons at -1l"C lost 20mgcm when the temperature as controlled to +1C, but the losses increased by over three-fold to 72 mg- when the temperature fluctuated by +6C. Both losses were measured over 220 days. 5.2.4 Retail display During retail display meat is particularly vulnerable to evaporative losses. The surface of meat displayed(without refrigeration) either hanging from rails or on shelves rapidly warms, and then quickly loses weight in dry mbient conditions. The problem of rapid weight loss is exacerbated by fluctuations in temperatures and by draughts from doorways or fansMore meat is now wrapped in impervious material before freezing, but, despite popular belief to the contrary, such packaging does not completely eliminate weight loss. Evaporative losses from polyethylene-wrapped carcass meat frozen at -30 °C are negligible, but losses of up to 0.5% have been recorded at -10 °C. The slower freezing time allowed water to migrate from the meat to the inner surface of the polyethylene. No published information has been located of the effect of RH on weight loss during frozen storage presumably because of the difficulty of measur￾ing RH at temperatures below 0 °C. Figure 5.1 shows clearly the detrimen￾tal effect of both air movement and high storage temperatures on weight loss. Although weight losses per day in frozen storage are small, storage times can be long with consequent overall losses as high as 10% (Roussel and Sarrazin, 1970). The importance of temperature control as well as actual temperature is supported by French experiments (Gac et al., 1970). Lean beef stored in cartons at -11°C lost 20mgcm-2 when the temperature was controlled to ±1 °C, but the losses increased by over three-fold to 72 mg cm-2 when the temperature fluctuated by ±6 °C. Both losses were measured over 220 days. 5.2.4 Retail display During retail display meat is particularly vulnerable to evaporative losses. The surface of meat displayed (without refrigeration) either hanging from rails or on shelves rapidly warms, and then quickly loses weight in dry ambient conditions. The problem of rapid weight loss is exacerbated by fluctuations in temperatures and by draughts from doorways or fans. 92 Meat refrigeration 30 80 120 225 340 8.1 6.4 4.2 3.6 5.2 7.2 2.2 3.2 5.1 1.8 2.8 4 0.8 1.7 Weight loss (%) 2.8 Storage (days) 10 8 6 4 2 0 –20 °C forced ventilation –16 °C free convection –26 °C free convection Fig. 5.1 Weight loss from unwrapped hams in frozen storage (source: Malton and James, 1984)