These days cooking a turkey requires little skill, because they often come with a handy pop-up timer already inserted in the top.

A turkey is finished cooking when the inside temperature reaches about 85 degrees Celsius. That’s the temperature at which the timer pops up to let you know the meat is ready. It’s an ideal device for an unskilled chef like me because it requires no judgment. When the red cap pops up, it’s done!

The pop-up turkey timer involves a little red plastic stick which is held in a blob of soft metal alloy, similar to solder. Many metal alloys melt at low temperature. They are usually made from mixtures of metals like bismuth, lead or tin. Their melting temperature can be adjusted by changing the percentage of one or more of the components. When the blob of soft metal alloy in the tip of the timer turns to liquid, at about 85 degrees Celsius, it frees the end of the red stick that is held in the solid metal. A spring makes the red stick pop up, and lets you know the turkey is ready.

Incidentally, you can reuse these timers by dipping the tip into boiling water, remelting the metal, and then pushing the pop up stick back into the metal. When it cools, the timer is ready to use again.

So next time you cook a turkey, you can impress your guests by explaining how the pop-up timer works.