Last week we left our wildlife friend, Mr. Turkey, exposed and thermally obvious. You can imagine what happened between then and this week.
So let’s talk again talk about capacitance , the thermal concept so fundamental to much of our work. Whether you buy a frozen turkey, or a fresh one, or even if you hunt your own, you must always be careful to cook the bird with the proper timing.
Especially when they are stuffed, turkeys are quite massive. In the oven, the exterior of the bird heats rather quickly by both convection and radiation. We can see this in the browned skin, and when poorly cooked, the dried out quality of the meat.
Heat transfers into the interior of the bird by conduction, a fairly slow process driven in part by the temperature difference between the oven and the inside of the bird. This means the heat transfer happens faster in the initial part of the cooking process and slows down as the bird finishes.
Cooking turkeys that are not fully thawed is asking for trouble. What is not obvious is that getting the frozen bird from 31°F to 33°F requires a great deal of energy. Typically ten times more energy is needed to melt the frozen meat than was required to get it up from the freezer temperature up to 31°F! Plus that latent heat of fusion does nothing to warm the bird up and on its way to being cooked. Failure to not fully thaw a bird prior to cooking has been the cause of many a delayed dinner, some tears, and no doubt a few sore stomachs.
Turkey, by itself, is no more susceptible to bacterial contamination than many other foods, but the industrial processing of turkey en masse has contributed to a number of such instances. This means we need to thaw and cook the turkey with great care to ensure the entire bird reaches a temperature for a long enough period of time that harmful bacteria is killed. Typically this means, once thawed, cooking the bird to a recommended minimum temperature of 170-180°F throughout.
If all goes well, and thankfully it often does, we should be able to enjoy a happy ending to this thermal tale.
John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner