How Do Pop-Up Turkey Timers Work?

The USDA National Agricultural Statistics Service estimates that 250 million turkeys will be raised in the US in 2009. If recent trends continue, some 45 million turkeys will be eaten this Thanksgiving. Some of those birds will be outfitted with a wonderful little piece of technology that tells you, in a very straightforward manner, when the turkey is ready to come out of the oven: the pop-up timer.

Pop-up timers are pretty simple machines. They're normally composed of a pop-up stick (usually plastic) attached to a spring and held in place by a blob of food-grade soft metal or wax at the bottom of the timer.

These three parts are held in a plastic casing. If you're wondering if the turkey is done, the timer gives you a "yes" or "no" answer. When the turkey is done cooking, the indicator stick pops up. If you peek in the oven and the stick hasn't popped up yet, the turkey's not done. It's fool-proof.

How does the timer issue its proclamations with such concrete certainty? Â Depending on who you ask, turkey is done when it reaches 165-180 degrees Fahrenheit. The trick is holding the pop-up stick in place with a wax or metal that will melt somewhere in that temperature range. When the correct temperature is reached, the melted anchor frees the pop-up stick and the spring launches the stick up into its "Hey, the turkey is done!" position.

[Image courtesy of Flickr user Tatu Damberg - Mixirica.]