The Coldest Point in a Real Pot: How Long After the Surface Simmers the Middle of a Thick Stew Is Safe

The surface of a stew can simmer while its centre is still cool, because heat must travel inward and a thick stew suppresses the currents that would carry it. This paper computes that delay with a radial multi-node conduction model using stated effective conductivities that combine conduction and convection. The base pot holds 8 litres, with radius 0.13 m, density 1050 kg per cubic metre, and specific heat capacity 3800 J per kg per kelvin. The outer surface rises from 20 °C to 100 °C in a stated 15 minutes and then stays at 100 °C. Without stirring, at a stated effective conductivity of 12 W per metre per kelvin, the surface passes 75 °C at 10.3 minutes but the centre does not reach 75 °C until 34.5 minutes, a lag of 24.2 minutes, and does not reach 90 °C until 49.4 minutes. With stirring, at a stated effective conductivity of 60 W per metre per kelvin, the centre reaches 75 °C at 14.9 minutes, a lag of only 4.6 minutes. Across pot volumes from 4 to 16 litres at fixed height, the unstirred lag to 75 °C grows from 11.5 to 50.3 minutes, while the stirred lag grows only from 2.3 to 9.1 minutes. A simmering surface is therefore not evidence that the middle is hot; the extra time, or stirring, is the safety margin. SIMULATED, NOT MEASURED.