Yeast

Yeast (also called leaven) is an ingredient used for making bread and alcoholic beverages.

Empath: The Luckiest Smurf stories
In the EMPATH: The Luckiest Smurf story series, yeast is used by Greedy and Biscotti Smurf in their baking and also by Tapper and Vino in their making of wines and fermented drinks. During Easter, Tapper has Biscotti make unleavened bread for his yearly communion service with his fellow Smurfs to commemorate the reason that he celebrates the holiday.