Cooling Systems for Transport of Unpreserved Milk Samples

Abstract

Two separate investigations of milk sample coolers are reported. A study conducted by the Milk Marketing Board of England and Wales demonstrated that an insulated box with eight ice (gel) packs (precooled to –20°C for 40h) would, under extreme conditions of high ambient temperature (up to 30°C), maintain 40 30-ml samples at less than 4°C for 48h or more. In practice, samples are delivered within about 30h of collection and ambient temperatures generally are about 20°C, lessening the need for extended deep freezing time for ice packs and making the system very applicable to UK conditions. This convenient and labor-efficient system has been used effectively in England and Wales since 1982.A study completed at the Ontario Central Milk Testing Laboratory evaluated milk sample coolers consisting of high density polyethylene cooling inserts in single- or double-walled insulated coolers. The essential features are rapid cooling (15°C to less than 4°C in 20min and to .5°C in 40min), constant temperature at .5°C for the required duration, and no direct contact between the sample vials and the coolant. Ice water is the coolant for short delivery times (up to 24h). For longer delivery times (up to 4 days), the cooling insert is charged with Styrofoam chips (50% volume) and water before freezing at –15°C. Design features and evaluation studies, including time and temperature profiles, are described.