Step 1Turn the light on in the oven (only the light). Pour 1/3 cup (80 ml) of the warm water into a bowl. The temperature should be about 40 °C/ 100 °F, but no more than 45 °C/ 110 °F. If you don't have this option on your oven, preheat the oven to the lowest setting (mine is 50 °C/ 120 °F). Open the oven for about 30 seconds to cool down slightly before placing the yeast inside and close the door.