After years of troubleshooting failed loaves, I've found almost every dense, gummy, or flat sourdough comes down to one of three fixable problems:

1. A weak starter. If it doesn't double in 4-8 hours after feeding and smells like nail polish remover instead of tangy-sweet, it's underfed. Feed it 1:1:1 twice a day for 3-5 days before you bake with it again.

2. Underproofed bulk fermentation. Gummy crumb is almost always this. Your dough needs to grow 30-50% in volume — not just look 'jiggly.' Go by volume and time, not vibes. At 75°F expect 4-6 hours with a healthy starter.

3. Wrong dough temperature. A cold kitchen can add hours to your timeline that most recipes don't account for. If your kitchen runs under 70°F, add 1-2 hours to whatever the recipe says.

Most people blame their flour or their technique when it's actually just one of these three variables running out of spec. Diagnose the right one and the fix is usually simple.