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Was the starter consistency exactly the same in all jars? Even small differences in hydration or thickness can affect rise and fermentation speed.
Residue or Cleaning Agents
Sometimes traces of soap or residue in one jar can inhibit yeast activity. Glass jars are easier to clean thoroughly, but if the plastic jar had some residue, that could slow or stop fermentation.
Starter Inoculation
Were all jars inoculated with the exact same amount and same portion of starter? Small differences can lead to big changes in activity.
Contamination or Yeast Imbalance
The jar that didn’t rise might have been contaminated with something that killed the yeast or shifted the microbial balance.
Can you fix it?
Feed it again with fresh flour and water — discard most of the sluggish starter and feed it again to give the yeast fresh fuel.
Stir well and keep at a warm, stable temperature (ideally around 75–78°F / 24–26°C).
Make sure the jar is clean and not airtight — use a loose lid or cover with a breathable cloth.
Try transferring some starter from your active jar to the sluggish jar’s container to “re-inoculate” it.
If it still doesn’t bubble or rise after a few feedings, consider discarding it and restarting fresh.
Summary
Differences in container temperature, material, seal tightness, or cleanliness can affect your starter’s activity even if feeding and location are similar. The good news: since your Ball jar starter doubled and fermented, it’s healthy and can be used to revive the other jar. Just refresh the sluggish starter by feeding or transferring some active starter into it.
If you want, I can help you create a simple step-by-step to revive a sluggish starter — just let me know!
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