In a large mixing bowl, combine the active levain, all-purpose or bread flour, whole wheat flour or whole spelt flour, and water. Mix the ingredients until they come together into a shaggy dough. Cover the bowl with a damp cloth or plastic wrap and let it rest for an autolyse period of 30 minutes.

Add salt and 10 g of additional water. Knead the dough thoroughly until it becomes smooth and elastic. Control the gluten development and the dough temperature. This process can take about 15-30 minutes. Adjust the hydration by adding more water if needed. Gradually add oil at the end of kneading either directly to the dough or into the bulk container.

Leave the dough in the container, cover it, and allow it to undergo bulk fermentation. This process typically takes around 5-8 hours or until the dough triples or quadruples in size. The ideal temperature for the dough during bulk fermentation is 24-25 C (75.2-77oF) for regular flour and 25-26oC (77.0-78.8oF) for strong flour. Or, when the dough has doubled in size after 3-6 hours, transfer it to the fridge for baking the day after. It will take 12-24 hours in the fridge depending on fridge temperature and your preference, until the dough triples or quadruples in size from its initial volume after kneading. No stretching and folding are required. Perform stretch-and-folds during the bulk fermentation at intervals of 30 minutes until the dough doubles in size. Then, leave it untouched to ferment until it triples or quadruples in size from the initial volume after kneading.