Warm-Up Characteristics of Cooled Liquid Sealed in a Thin-Packet: A Study

Milk is collected, processed and packed at milk processing centres far from user location. Refrigerated and insulated vans carry milk packets in crates to the city/town where they are offloaded at the milk distributor, then get distributed to local users (residents) during which it gets warm due to heat transfer from ambient. To keep low bacterial count, pasteurized milk needs to be kept between 5-10 °C during transport, distribution and storage. This works tries to characterize the warm up of milk in packets using liquid water as surrogate due to similarity in the properties. The warm-up was studied for single isolated packets as well as water packets packed in crate. Liquid water was sealed in food grade LLDP plastic packet and cooled in refrigerator to bring the temperatures down to 3-5 °C. The packets were then taken out and suspended in ambient air at different temperatures (18°-25°C) as well as water packets stacked in crate as is done while transporting. It has been found the single isolated water packets take 1.5 hours to raise by 6.5 °C (from 7.5 °C) while same packets stacked in crate takes 3.5 hours for the same temperature rise when subjected to 20°C ambient temperature.