Science Buddies: "Ask an Expert"

A question came up that we were struggling to answer confidently. When heating something in an oven, say a Christmas turkey, does the temperature rise faster or slower during the heating cycle. For example, the turkey might be at 36° D when put into an oven at 325° F. If we wanted to heat it to 160°, would the first half of the cook time, 36° starting +62°, be faster or slower than the last 62°? Would it all be the same, given the oven stays at exactly 325°? Why?

Thanks in advance!

Chris

chbrandt - A bit of a tricky question. Assume the air temperature in the oven is a constant 325 degrees. The food in the oven is heated by conduction from the outside source toward the core. Let's say you are cooking a meatloaf that is a perfect 5" diameter sphere. After several minutes, the temperature near the surface will rise, and slowly conduct heat toward the core. It depends on where you measure the temperature in the core of the meatloaf. If the meat starts out at 36 degrees, after 15-20 minutes, the temperature near the surface may be 325 degrees, but at the core, in the center, it might still be close to 36 degrees. It may take several hours before the meat is uniformly 325 degrees. The process of conduction may not be linear either, as the meat may lose moisture that may have an effect on the rate of conduction. If you choose a point in the meatloaf at say a depth of 2", you might measure the temperature at that depth after a certain time, then measure at a later period to determine time and heat rise, but I still don't think we have defined the answer as to the rate of temperature rise sufficiently.

Rick Marz

I hadn't thought of a lot of that. Maybe I should simplify the scenario to get at the real question we spent the most time on. Let's say instead we're heating a gallon of water. Would heating the water up, with a starting temperature above freezing and a final temp being below boiling point, be linear from start to finish?