Levain is a culture of flour and water that houses yeasts and bacteria. With food and time, it ferments the dough and takes part in the aroma, the flavor, and the structure. It is not a guarantee of the absence of gluten, nor of better digestion for any person.
Feeding the levain means renewing part of the culture with flour and water. The rhythm changes with the temperature, the type of flour, and the proportion. Watch the growth, the bubbles, and the aroma. A clean container and a recipe with defined amounts are worth more than racing against the clock.
Baker's percentage
In the classic notation, the total flour is worth 100%. Water, salt, and the rest are fractions of that flour. If the formula calls for 1,000 g of flour, 70% hydration, and 2% salt, the water is 700 g and the salt is 20 g. The sum of these three already describes the base dough.
The levain is not a fourth ingredient “on top” of that sum. It is made of flour and water that already go into the 100% and into the hydration. If 20% of the total flour goes to the levain (PFF — prefermented flour) and that levain is at 100% hydration, the little jar takes 200 g of flour and 200 g of water: 400 g of levain. Into the final bowl go 800 g of flour, 500 g of water, 20 g of salt, and the 400 g of levain. The dough weighs 1,720 g. Adding 1,000 + 700 + 20 + 400 = 2,120 g counts the flour and the water of the levain twice.
PFF is not the weight of the levain. PFF is only the flour that went into the little jar. The weight of the levain includes that flour and its water.
How to start at home
Choose a stable feeding — for example, equal parts of flour and water — and note the time, the kitchen temperature, and what you saw. When the culture doubles with a sour and sweet aroma, it is usually ready for the dough. If it smells of solvent or does not grow, feed it again and wait; do not force a bake.
The Library calculator does these sums without a model: you enter flour, hydration, salt, and the levain by PFF or by weight. The numbers on the page do not consume artificial intelligence.
This text opens the notebook. It does not replace professional bakery management, production cost, or human accompaniment.