Food cooling: Biot number and core temperature

When can an entire food product be represented by a single temperature?

An experiment from Cyril Voyant’s course, running in your browser. Full course and slides (French) · Choose another experiment.

The relationship to understand

Bi=hLc/λ; lumped model: T(t)=T∞+(Ti−T∞)exp(−t/τ), τ=mcp/(hA).

Try it and interpret

With h=25 W/m²/K, Lc=0.02 m and λ=0.5 W/m/K, Bi=1: internal gradients are not negligible. Increase λ to bring surface and core temperatures closer together.

Assumptions and limitations

The usual Bi<0.1 criterion is a guide. The other curve uses the first conduction term for a slab, valid after the earliest instants; properties and convection are constant, with no phase change. This does not validate a food-safety process.

Go further with the course

This page focuses on one concept. The full chapter (French) contains the reasoning, further examples, slides and FAQ. Demonstration values are computed or constructed within the stated model; they are not new research findings.