Hot food has to pass through the danger zone to get cold. The bigger the batch, the slower it cools, and a big pot in a refrigerator can stay warm in the middle for many hours.
Key idea
The Food Code's two-stage cooling rule: cool cooked TCS food from 135°F to 70°F within 2 hours, then from 70°F to 41°F or below within the next 4 hours: 6 hours in all. The first stage is the strict one, because bacteria grow fastest between about 125°F and 70°F.
| Method (Food Code 3-501.15) | Why it works |
|---|---|
| Shallow pans (food about 2 inches deep or less), uncovered or loosely covered until cold | More surface, less distance for heat to travel |
| Cut large items into smaller pieces | Thin pieces lose heat faster |
| An ice-water bath, stirring often | Water pulls heat far faster than air |
| Ice wands (frozen paddles) stirred in | Cool from the inside |
| Ice added as an ingredient (for soups and stocks) | The ice replaces some of the water in the recipe |
| Blast chillers and tumble chillers | Fast cold air or water made for cooling |
Why it works
If food reaches 70°F early, say in 1 hour, the FDA's handout says the remaining time still applies to reaching 41°F; the 6 hours in total is the outer limit. If food is not at 70°F within 2 hours, the Food Code says it must be reheated to 165°F and cooled again from the start, or thrown away, depending on the rules where you work.
Worked example: Did it pass?
Chili is 135°F at noon, 72°F at 2:00 p.m., and 40°F at 5:00 p.m.
- Stage 1: 135°F to 70°F must happen by 2:00 p.m. At 2:00 it was 72°F, still above 70°F.
- Stage 1 failed, even though stage 2 was fast.
Answer: It did not pass.
Worked example: Time left
Stock reaches 70°F 90 minutes after it was 135°F. By when must it reach 41°F, counting from 135°F?
- 6 hours in all from 135°F.
- It reached 70°F at 1.5 hours; the outer limit is 6 hours from the start.
Answer: Within 6 hours of the start (4½ hours after it hit 70°F).
Common mistake
Putting a lid on a deep, hot pot and putting it in the walk-in. The lid traps heat, the pot holds it, and warm air from it can warm nearby food.
Practice at home
- Make a pot of stock or soup. Split it: one half stays in the pot in the refrigerator; the other goes into a shallow pan set in an ice bath. Check both temperatures every 30 minutes for 2 hours and graph them.
The science behind it
- Newton's law of cooling: why the cooling curve bends