The mission here is to get the starter to a point where it’s rising as rapidly as possible because that’s going to result in bread that rises beautifully during fermentation and then again during baking.
To do this, we need the yeast to become HANGRY. And the more we feed them, the hangrier they get. They’re greedy – they’ll increase their rate of consumption to account for a surplus of available food (fresh flour and water).
As you’ll see in the video, we want to avoid excessive “over-proofing” – which is simply leaving the starter too long without feeding it. Over-proofing happens when the yeast consumes all the fresh dough (causing a nice rise) but then they run out of fresh dough to consume so they stop producing those fart bubbles. Without those gasses being produced by the yeast, the dough deflates and drops back down again.
The yeast also react to the lack of food by becoming less aggressive in the rate at which they consume fresh dough. So subsequent rises will be slower until the yeast adjust to surplus feedings again.
It’s not a big deal at all if the starter over-proofs. Over the long term, mine lives in a perpetual state of near-starvation in the fridge (with me only feeding it every week or two). Starters can survive like this indefinitely, the yeast is very resilient.
But when it comes time to bake something, that fast rise is crucial. So we need to feed the start a few times (discarding most of the starter each time we feed it) to get the yeast all voracious again.
Once the starter is good and active/hangry/fast-rising – we can move onto the next step toward baking something, which is to build a levain.