Obviously analog candy thermometers can’t use vials full of mercury like some domestic models, in case they break and spill poisonous liquid metal into your food. Instead, most of these devices will use digital displays or colored alcohol instead. Some non-mercury thermometers will use a special substance called Galinstan made from tin, indium, and gallium. Galinstan is non-toxic and will pass through the digestive system with no negative effects.