Cooking For Engineers

[mike]

Hi Mike – great sight, here’s my question.



Re; Thanksgiving Turkey



I understand that cook time versus weight is not linear – that makes sense to me. However, all things being constant, does a bird cook faster the longer it is in the oven? That is, if it takes 10 minutes to raise the core temp of the bird say, 15’celcius, does it take another 10 minutes to raise it another 15’C?



I’m not sure why, but I think not. The bird cooks from the outside in, leaving an ever decreasing surface area (or rather, an isothermal surface) over which the heat has to flow. Also, as the bird cooks, the mean thermal conductivity and specific gravity would be changing wouldn’t it….?



Cheers,



Mike

[FranksPlace2]

Well Heat Transfer 101 would say that the highest heat flux would occur when there is the largest temperature difference between the oven and the bird, that is when you first put it in.

However as the bird cooks, moisture evaporates and the specific heat goes down. So there is a larger temperature increase for the same heat flux.

All I know is the temperature seems to increase the fastest right at the end of cooking. So watch it.

[Chef Bob]

heat moves through food only through convection.

as the molecules move faster (inc in temp) that heat is transfered faster.

so if the bird is say 400 degrees F on the outside that heat will be transfered very fast to the inside....the bird starts out ar 38 degrees F until the outside heats up to a high temp...very little energy is transfered to the inside so small temp increase for a while till the thing actuall heats up on the outside....

also air is a crappy medium for convective cooking.....FAT is more dense so cooked in a fryer at 4oo degrees will take way less time as more molecules are hitting the outside of the bird per second thereby heating the outside and transfering their energy much faster.