On Thanksgiving, millions of home cooks will rely on a wonderful little piece of technology to tell them when the turkey is ready to come out of the oven: the pop-up timer. It’s foolproof—just peek, and if the stick hasn’t popped up yet, keep cooking. How does the timer issue its proclamations with such concrete certainty?
It’s ingeniously simple. The plastic pop-up stick attaches to a spring that is held in place by a blob of food-grade soft metal or wax. When just the correct temperature is reached—usually about 165 degrees indicates a cooked-through turkey—the soft metal or wax anchor melts, freeing the spring and launching the stick into its “hey, the turkey is done!” position.