temperare

Temperāre in Latin meant to mix properly, to moderate, to regulate. The word is about balance — bringing elements into correct proportion. It entered English through Old French temprer in the thirteenth century and immediately acquired multiple meanings: to moderate one's anger (to temper one's response), to harden metal by heating and cooling (to temper steel), to tune a musical instrument (temperament), and eventually to control the crystallization of chocolate.

Tempering chocolate is about polymorphism. Cocoa butter can crystallize in six different forms, numbered I through VI. Only Form V produces the glossy, snappy, smooth-melting chocolate that confectioners want. Tempering achieves Form V by heating chocolate to 50°C (melting all crystals), cooling it to 27°C (allowing Forms IV and V to seed), then reheating it to 31-32°C (melting the unstable Form IV crystals and leaving only Form V). The process is precisely what the Latin word described: bringing elements into due proportion.

Tempering eggs is a different technique with the same word: slowly adding hot liquid to beaten eggs to raise their temperature gradually without scrambling them. The goal is the same as with chocolate — controlled change. If you dump hot liquid into cold eggs, the proteins seize. If you add the liquid slowly, stirring constantly, the eggs warm evenly and thicken the mixture smoothly. Temperāre: to mix in due proportion.

The word temper appears across English in dozens of contexts — temperament, temperature, temperance, temperate, tempo — all from the same Latin root. Each one is about proportion, moderation, or measured change. The word family is the largest single-root network of English words related to the concept of balance.