How long until the pizza is ready to eat?

A pizza comes out of the oven at 90 °C. How long does it take to cool to ready to eat — and what's the difference between leaving it on the kitchen counter (20 °C) or putting it in the fridge (5 °C)?

The 60 °C criterion

We take 60 °C (pizza average temperature) as "ready to eat". Threefold rationale:

It's the food-safety threshold for holding hot food (above 60 °C).
On brief contact it no longer scalds the mouth.
Still pleasantly hot.

When the average reaches 60 °C, the surface is already cooler (safe) and the centre a little hotter.

§1Results — time to 60 °C

Scenario	Ambient	Support	Convection only	With radiation	Reduction

§2Cooling curves

Solid line = convection only; dotted line = with radiation (same colour per scenario). The shaded band spans from the coldest point (edge/surface) to the hottest (centre) — its width is the internal gradient (Biot ≈ 0.3).

§3Temperature field & plume

2D vertical slice of the domain: the pizza (rectangle) and the natural-convection plume of hot air.

Field:

t = 0 s

Generated with OpenFOAM v2412 · chtMultiRegionFoam (laminar, natural convection ± fvDOM radiation) · 2D mesh ~4800 cells · pizza ρ=700, c_p=3000, κ=0.40, ε=0.9 · 8 simulations.