Troubleshooting - Slow or Stalled Yeast
Root Causes of Slow or Stalled Fermentations
These are some common root causes of slow or stuck beer fermentations:
Unhealthy yeast (stressed, insufficient nutrient, stored for too long, damaged during shipping)
Stressed yeast can cause slow or stalled fermentations. This can be due to the yeast being too old, or having insufficient nutrients to complete the fermentation. Another possibility is damage to the yeast during shipping or handling. In most cases, adding nutrients such as Yeast Lightning Nutrient can help to restart a stuck fermentation.
Wort production variability (changes in brewhouse, base malt spec, too much or too little trub carryover)
Changes in brewhouse equipment and function, base malt specifications, as well as amount of trub carryover can impact fermentation.
For more information, see our pages on attenuation as well as the forced fermentation test.
Temperature swings
At the homebrew scale, fermenting in ambient household conditions can mean significant temperature swings that may impact fermentation.
At the professional scale, glycol cooling setups may impact yeast performance. For example, if the glycol jacket on the tank cone is cooler than the tank upper jacket, this can cause premature flocculation/dormancy. This is a common issue with cylindroconical tanks due to the lower surface area to volume ratio of tank cones versus jackets. In this case we recommend restricting the glycol flow to the cone jacket.
Really low glycol set temperature can also result in temperature swings when the tank calls for glycol. This can cause over-cooling and increase lag time. This is especially evident in lager worts pitched at a warmer temperature than the setpoint. If these fermentations over-cool you may observe an extended lag time. For lagers, it is often better to either start the wort cooler than the setpoint, or gradually cool the tank to the set point in 1ºC increments.
Another professional brewery glycol-related issue is if the glycol piping system is designed with a first-in-first-out scheme to reduce cost, the system will be prone to temperature swings. First-in-last-out schemes typically result in more regularity in fermentation temperatures due to less swings in temperature.
Yeast-inhibitory ingredients
Some ingredients can have antifungal properties and will slow down or stall out yeast. Here is a list of ingredients we have encountered which have been shown to have potential to inhibit yeast:
- Citrus (in high concentrations)
- Ginger
- Adjuncts solubilized in ethanol (e.g. vanilla extract) For these ingredients, we recommend adding post-fermentation.
How to restart a stuck fermentation
These are the steps we recommend for restarting a stuck fermentation:
1. Add nutrients and rouse the yeast
You can do this at homebrew scale by shaking the vessel, and at professional scale by rousing with CO2 or nitrogen bubbling through the bottom. We do not recommend oxygenating beer that is more than 50% attenuated. We recommend using Yeast Lightning Nutrient.
2. Pitch a dry yeast such as House Ale
Dry yeast does not require oxygen and a robust strain such as House Ale is perfect for restarting stuck beer fermentations. Since House Ale is highly alcohol-tolerant it can even be used to shave off gravity points in Imperial Stouts and Triple IPAs when needed.
Troubleshooting Questions for Stuck and Stalled Fermentations:
1. What is the yeast generation? If you have viability %, what was that?
2. How old was the yeast from the time it was cropped to when it was used?
3. How was wort oxygenation performed?
4. What is the grain bill and original gravity of the wort?
5. Did you add nutrients?
6. Do you perform a forced fermentation test? If so what are the results?
7. How much trub carryover do you allow in the wort?
8. Does the tank have independent control of the cone and body glycol jackets?
9. Was the yeast direct pitched from Escarpment Labs or propagated at the brewery?