Direct answer first: Sourdough starters can go bad in a few clear ways, and you can check for common signs to know whether to revive or discard it. Key signs your starter may be bad

• Visible mold: Any fuzzy or colored spots (pink, orange, green, blue, black) on the surface or sides means discard the starter and start fresh. Mold indicates contamination that cannot be safely revived.

• Rotten or off-putting smell: Healthy starters usually smell yeasty, tangy, or fruity. If the aroma is foul, rotten, or resembles garbage, you should discard it. A strong, unpleasant odor is a strong red flag.

• Unusual color or texture: While hooch (liquid) on top can be normal, an entire starter that looks pinkish, brownish-gray, or otherwise discolored beyond normal variation is a sign it’s gone off.

• No activity after feeding: If after regular feedings (with fresh flour and water) there are no bubbles, no rise, and no visible activity for several days, the starter may be dead or in need of a long revival process.

• Repeated failure after revival attempts: If attempts to revive over multiple feedings at warm room temperature fail, it’s safer to start over.

What to do if you observe these signs

• If you see mold or persistent odd colors: discard the starter and begin a new one from scratch or from a known healthy starter you’ve kept in reserve.

• If the smell is off but there’s no mold: you can attempt a revival, but proceed with caution. Re-feed with fresh flour and water, keep at a stable warm temperature, and monitor for several days. If signs of activity return, you can continue; if not, discard.

• When in doubt, err on the side of safety: contaminated starters can pose health risks, so discarding and restarting is often the best course.

If you’d like, describe what you’re seeing (smell, color, surface, and any bubbles after feeding), and I can help interpret those signs and guide the revival or discarding decision with tailored steps.