Guides
Starter problems, sorted
Most strange starter behavior is harmless, and a few signs mean the jar has to go, with no exceptions. Start with the starter that will not rise, then find the smell, the liquid or the color you are looking at.
New here? Read Sourdough Starter Not Rising: Every Cause and Fix first. A sluggish starter is almost always too cool, too young or underfed, and that guide walks through each cause in the order worth checking. The rest of this section takes one symptom at a time: the liquid on top, the smells, a runny jar, a starter that rises and falls before you can use it, and the colors that mean it is over.
Two lists settle most worries. Throw it out: fuzzy mold of any color, pink, orange or red streaks, a rotten or putrid smell, or a slimy texture that will not stir back in. Feed it and carry on: gray, brown or dark liquid on top (hooch), a smooth dry skin with no fuzz, a nail polish or vinegar smell, and a young starter having a quiet few days.
Try it
Most slow starters are on the wrong ratio for their room. The starter feeding calculator shows the usual hours to peak for each ratio in a cool, average or warm kitchen.
Heads up
Food safety wins every time. If anything in the jar is fuzzy, pink or orange, discard the whole starter, do not scrape off the spot, and wash the jar in hot, soapy water before you begin again. When in doubt, throw it out.
Guides in this section
Coming soon: Hooch on Sourdough Starter: What the Liquid Means; Sourdough Starter Mold: What It Looks Like, What to Do; Starter Smells Like Nail Polish or Acetone? Read This; Hooch or Mold? Telling Them Apart in the Jar; Is My Sourdough Starter Dead? How to Tell and Fix It; What Should a Sourdough Starter Smell Like?.