After its overnight slumber, your levain should show some signs of activity.

Smell and poke the dough; appreciate how these simple ingredients transformed overnight. There should be some bubbles in the dough - that's the yeast generating gas, which will leaven the loaf in the oven. The levain may smell funky or have just a hint of sour, depending on time and temperature.

These are early signs of microbial activity that will continue to evolve and progress.

We will now add more flour mixture and water, and then build gluten, the protein network that lets the dough rise tall. Think of the dough like a bunch of tiny balloons - the small and/or large holes you see in a finished loaf. We want to have strong balloon walls (gluten) so the dough can fill with air and rise without collapsing.