Roman bakers used wood-fired ovens calibrated by hand timing. They held their hands inside the chamber and counted seconds until heat became unbearable. Surviving manuals from 100 CE specify counts between 8 and 12 seconds for bread, 15 to 18 for delicate cakes. Modern temperature measurements confirm this correlates to 375-425°F ranges.
Medieval Clay Testing Standards
By 1200 CE, German bakers placed small clay tablets inside ovens. These tablets changed color at specific temperatures, creating a visual reference system. Archaeological digs have recovered these tablets with distinct color bands corresponding to 300°F, 350°F, and 400°F thresholds. The system worked reliably enough that guilds standardized tablet composition across regions.
Paper and Flour Methods Emerge
Dutch bakers in the 1600s documented placing white paper inside ovens. If it turned golden brown in 30 seconds, temperature suited cake baking. If it blackened immediately, the oven was too hot. They also tossed flour handfuls onto oven floors, observing burn rates. These practical tests gave consistent results that match modern thermometer readings when replicated today.