A priceless treasure transmitted as a family legacy, from batch to batch, from baker to baker, it was formerly made out of apples, or pears that were fermented for a few days in some water then ground. It is now extracted from molasses from beet or cane sugar. A good leaven will be kept over from one batch to the next and will form in two or three days. Refreshed several times and fed with flour, it appreciates the caress of the bakers’ palms. When it rises up, watch it like milk on fire, wrap it up and keep it warm, without forgetting, from time to time, to powder it with some flour so that it would not wrinkle. The leaven is the baker’s kid. It is the soul of the bread. It carries its memories.
By superstition, some put half an onion over its back or a few cumin seeds to spice up the way its tastes.

A Gourmet's notebook