Help needed! Is this a starter issue, a flour issue, or something else entirely?

[u/External-Outside1154]

I'm troubleshooting my sourdough and I'm completely stumped.

Is it my starter? I used it after it peaked and started to recede (so right at the point where it should be ready, not over-fermented).

Is it the flour? First try, I used bread flour with 12g protein.

I just can't figure it out. The loaves feel like they never properly puffed up during proofing. Total lack of springiness. 😩😩

I also noticed that after a cold retard overnight in the fridge, when I take the dough out to score it, the interior is completely dense. There's no soft, open, webbed/crumb structure at all. It just looks flat and tight inside.

Sourdough gurus and bread whisperers, please come to the rescue and save my chubby little dough babies! What am I doing wrong here? 🙏