Fundamentals of Food Preservation & Cold Chain Control
Food degradation occurs via three primary mechanisms: microbial proliferation (bacteria, molds, yeasts), enzymatic breakdown, and chemical oxidation.
The USDA “Danger Zone” Rule
Bacterial growth accelerates rapidly between 4°C and 60°C (40°F and 140°F). Pathogenic bacteria such as Bacillus cereus, Salmonella, and Staphylococcus aureus can double in population every 20 minutes in this range.
Refrigerator Temperature Zones
- Upper & Middle Shelves (3–4°C / 37–40°F): Most stable temperatures; ideal for dairy, cooked leftovers, and deli items.
- Bottom Shelf (1–2°C / 34–36°F): Coldest zone; always reserve for raw proteins (poultry, beef, fish) in sealed trays.
- Door Bins (5–8°C / 41–46°F): High temperature fluctuation due to door opening; use for condiments and pasteurized juices, never for fresh milk or eggs.
