164 Meat refrigeration Table 8.2 Advantages and disadvantages of different thawing system Advantages Disadvantages Easy to install: can be Very slow, unless high tems adapted from chill rooms. velocities and high ow velocity systems temperatures are used retain good appearance then there can b weight loss, spoilage and appearance problems Faster than air systems Effluent disposal. microbiological ndition Unsuitable for composite blocks Vacuum-heat Fast Deterioration in Very controllable ane Batch size limited Electrical Microwav Problems of limited systems Infra red absorption Can cause High Resistive Problems of contact on irregu 8.3.1.1 Air thawing Air thawing systems transfer heat to the frozen material by conduction through the static air boundary layer at the product surface and the rate of heat transfer is a function of the difference in temperature between the product and the air and the air velocity. Air systems are very flexible and may be used to thaw any size of meat cut from whole carcasses to individ- ual steaks 8.3. 11.1 Still air Thin blocks(<10cm) of meat can be thawed overnight at room tempera ture and, provided the surface of the product does not become too dry, the thawed product can be perfectly acceptable. Air temperatures should not be greater than15°C For thicker materials still air thawing is not recommended, since thawing times extend to days, rather than hours, and the surface layers may become8.3.1.1 Air thawing Air thawing systems transfer heat to the frozen material by conduction through the static air boundary layer at the product surface and the rate of heat transfer is a function of the difference in temperature between the product and the air and the air velocity. Air systems are very flexible and may be used to thaw any size of meat cut from whole carcasses to individ￾ual steaks. 8.3.1.1.1 Still air Thin blocks (<10 cm) of meat can be thawed overnight at room tempera￾ture and, provided the surface of the product does not become too dry, the thawed product can be perfectly acceptable. Air temperatures should not be greater than 15 °C. For thicker materials still air thawing is not recommended, since thawing times extend to days, rather than hours, and the surface layers may become 164 Meat refrigeration Table 8.2 Advantages and disadvantages of different thawing systems Advantages Disadvantages Conduction Air Easy to install: can be Very slow, unless high systems adapted from chill rooms. velocities and high Low velocity systems temperatures are used, retain good appearance when there can be weight loss, spoilage and appearance problems Water Faster than air systems Effluent disposal. Deterioration in appearance and microbiological condition. Unsuitable for composite blocks Vacuum-heat Fast. Deterioration in (VHT) Low surface temperatures. appearance. Very controllable. High cost. Easily cleaned Batch size limited Electrical Microwave/ Very fast Problems of limited systems Infra red penetration and uneven energy absorption. Can cause localised ‘cooking’. High cost Resistive Fast Problems of contact on irregular surfaces