Troubleshooting - Slow Kettle Sours

Root causes of slow or stalled kettle/quick sours 

- Temperature too high. The optimal temperature for most Lactobacillus strains used in brewing is 37ºC. 
- Too much oxygen/air can slow down certain strains like Lactobacillus plantarum. 
- Souring in a kettle and using the jackets/elements to maintain temp is risky - Lacto settles and may overheat in hot spots. 
- Lacto ferments can stratify, e.g. different pH in different parts of the tank. We suggest rousing to get a representative sample. 
- Residual IBU/hop material from a previous brew in the kettle, whirlpool, or heat exchanger can cause minor carryover of bacteria-inhibiting compounds, causing slow or incomplete souring by hop sensitive Lacto strains. 
Questions that will help us help you: 
1. What is the souring/pitch temperature? 
2. Do you purge with CO2? 
3. What vessel do you sour in? 
4. Do you recirculate/rouse the ferment? 
5. Was the brewhouse CIP'd prior to the unhopped wort brew? 
6. Do you notice any off flavours? Could you describe it? 
7. Did you rouse/mix the tank prior to sampling to get a representative sample? 

Additional Resources 
Lactobacillus 101 on YouTube
The Road to Lacto 2.0 on YouTube

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