If your sourdough starter is bubbling but not rising, it is usually a sign that it is active but lacks the structural integrity or environment to trap the gas it’s producing.
1. The Consistency is Too Thin
The most common culprit is a "runny" starter. If your starter is the consistency of pancake batter, the carbon dioxide bubbles will simply float to the top and escape rather than pushing the starter upward.
The Fix: Use a kitchen scale to feed equal parts flour and water by weight, not volume. If it is still thin, try a "dry feed" by adding slightly more flour until it reaches a thick, paste-like consistency similar to Greek yogurt or thick mustard.
The Fix: Be patient and continue daily feedings. It can take 2 to 4 weeks (or longer in cold weather) for a starter to become fully mature and rise reliably.
2. Temperature is Too Low
Yeast activity slows down significantly in temperatures below 70°F (21°C). In a cold kitchen, your starter may produce bubbles very slowly without ever gaining enough momentum to double in size.
The Fix: Move your starter to a warmer spot, such as the top of the refrigerator, inside an oven with the light on (turned off), or use warm water (80-90°F) for feedings.
3. Low-Protein Flour
Flours with lower protein content, like some All-Purpose flours, have a weaker gluten network and cannot trap gas as effectively as Bread Flour or whole grains.
The Fix: Try incorporating a portion of Whole Wheat or Rye flour into your feedings. These flours contain more nutrients and wild yeast, which can give your starter a significant boost.
5. Overfeeding/Dilution
If you feed your starter too frequently (e.g., twice a day) before it has had a chance to peak, you may be diluting the yeast population before it can establish itself.
The Fix: Stick to once-daily feedings at a 1:1:1 ratio (starter:flour:water) by weight until you see a predictable rise and fall.