Today on A Moment of Science, we solve yet another common kitchen mystery. You've seen them sticking out of store-bought turkeys, and have counted on them to let you know when they're cooked to perfection. What are they? Pop-up Timers!
In an effort to take some of the guesswork out of cooking turkeys, pop-up timers are often installed in butchered turkeys to indicate when they're done. They have four parts: an outer case, a spring, the little red stick that pops up when the meat is cooked and a little blob of metal that's similar to solder. This soft metal is solid at room temperature, but melts at about 175 degrees Fahrenheit, or 80 degrees Celsius.
So, to begin with, the spring in the pop-up timer is compressed and the little red stick is trapped in the metal. Then, when the turkey reaches a nice steamy temperature, the metal melts and frees the little red stick, and the spring causes it to pop up.
Here's a tip for the thrifty among you: pop-up timers are actually reusable. All you need to do is boil some water and dip the tip of the timer into it. This will re-melt the metal, and then you'll be able to push the stick back into position. Once the timer cools, it's ready to go again.