Cooling Systems for Transport of Unpreserved Milk Samples

¹ Ontario Ministry of Agriculture and Food, 95 Stone Road, West, Guelph, Ontario, Canada N1G 2Z4

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 48 h) would, under extreme conditions of high ambient temperature (up to 30°C), maintain 40 30-ml samples at less than 4°C for 48 h or more. In practice, samples are delivered within about 30 h 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 20 min and to .5°C in 40 min), 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 24 h). 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.

Key Words: transport • milk sampling • cooling systems

Submitted on February 12, 1990
Accepted on April 19, 1990