STORAGE STABILITY OF COMMERCIAL MILK1

Abstract

Storage of fluid milk for extended times at low temperature appears feasible. The extended shelf life is long enough to allow a 100-fold decay of Iodine-131 under emergency conditions. This theoretical decay period may be 4 to 8 weeks depending on degree of contamination and extent of depositions on pasturage. Commercially produced summer milk stored at 32 F, averaged 4.4 weeks or 5 times its life at 45 F. Summer milks possessed twice the shelf life of winter milks. Shelf life was materially affected by pasteurization temperature, storage temperature, and season as determined by taste panel and bacteriological tests. Marked increases in shelf life were observed with reduced storage temperatures. Criteria for product acceptability were flavor score (35.0 or higher), total plate count, and psychrophilic plate count (less than 1 million per ml). UHT processing at 200 to 220 F for 0.5 to 16 sec yielded as much as 20 weeks acceptable shelf life at 32 F. A combination of UHT pasteurization, 32 F storage to the end of microbial lag phase, and repasteurization followed by refrigerated holding extended storage life to as much as 23 weeks, depending on storage temperature.