Question

Baked potatoes are normally wrapped in aluminum foil. How does this affect the cooling of the potato after it is removed from the oven? (Consider radiation)

Answer 1

There are three basic methods for transferring heat from one object to another: conduction, convection, radiation. Conduction is the method we are most familiar with. Conduction is a hot object touching a cold object. Convection is moving liquids and gases carrying heat from one location to another. An example of this is air circulating through ducts and vents. Neither of these has anything to do with color.

Radiation is radio waves, microwaves, light waves , x-rays, etc. carrying heat energy from one surface to another. Visible light depends on color. In the dark, there is no visible light. Infrared light is the most common heat transfer radiation in the dark. Some material can easily absorb infrared radiation, and some cannot.

What does affect it is "shininess". A shiny surface is very smooth. It is easier for any radiation to reflect from a smooth surface. Shiny metallic surfaces tend to be smoothest and best reflective. This is not due to color: a smooth metallic surface has no little grooves or holes in which to trap extra waves. Color as we define it only relates to visible light.

One comment about a baked potato: in an oven very little heat transfer is due to radiation. The majority results from hot air coming in contact with the potato, or with the foil around it. I do not expect the shininess of the foil will make a big difference. It is important that foil make very good contact with the potato. Air pockets between the foil and potato act as insulating zones, slowing the heat transfer.

Regarding foil-wrapped baked potatoes : When heated in a conventional oven, the foil around the potato reflects incoming heat. However, the foil itself heats up and ultimately transfers heat to the potato, thus allowing it to cook. Once cooked and removed from the oven, the foil reflects heat back to the potato so that it stays warm longer than if it had been immediately unwrapped.