“Pain au Levain” is French bread made from a sourdough starter. It is a dense bread, usually round or oblong, with a very delicate tang to it. The sour tang — or the acidity (“acidité”, as the French refer to it), helps to hold moisture in the bread, which makes it stay fresh longer than breads made with yeast.
There are 3 different kinds of starter that Pain au Levain can be made with, starting from the “chef” starter. The taste will vary depending on the starter used. See French Starters for more information.
The production of Pain au Levain has been regulated since September 1993 by Decree # 93-1074 (called the “Décret Pain” — bread decree) which states that to be called “Pain au Levain” the pH of the bread must be no greater than 4.3 and the bread must have an acidity of at least 900 parts per million. (“un potentiel hydrogène (pH) maximal de 4,3 et une teneur en acide acétique endogène de la mie d’au moins 900 parties par million”.)
Some home recipes will use a Poolish as a starter instead of a sour starter, but the product wouldn’t have the necessary acidity to be sold legally as “Pain au levain.”
“Pain au Levain” is now more of an artisan, specialty bread.
The French will often use Pain au Levain to accompany cold cuts and cheeses.