How To Restart A Fermentation

Fermentation is a critical process in brewing, where yeast converts sugars into alcohol and carbon dioxide. However, there are instances when fermentation may stall or stop prematurely. This can occur due to various factors, including insufficient yeast health, inadequate temperature, or lack of nutrients. Restarting a fermentation can be essential to achieving the desired alcohol content and flavour profile in your brew. Below are the steps and considerations for effectively restarting a fermentation.

1. **Assess the Situation**: Before taking action, it is important to determine why fermentation has stalled. Common signs include a lack of bubbling in the airlock, a stable specific gravity reading over several days, or an off-flavour developing in the brew. Understanding the cause will help guide the appropriate response.

2. **Check Temperature**: Yeast activity is highly dependent on temperature. Most yeast strains thrive between 65°F and 75°F (18°C to 24°C). If the fermentation temperature has dropped below this range, gently warming the fermenter can help reactivate the yeast. Avoid rapid temperature changes, as this can shock the yeast.

3. **Rehydrate Yeast**: If the yeast is determined to be inactive or unhealthy, adding fresh yeast can be an effective solution. Use a high-quality brewing yeast, such as Wyeast Brettanomyces Lambicus Yeast, known for its unique flavour profiles. Rehydrate the yeast according to the manufacturer's instructions before adding it to the fermenter. This process typically involves mixing the yeast with warm water and allowing it to sit for about 15 minutes.

4. **Nutrient Addition**: Sometimes, yeast may stall due to a lack of nutrients. Adding a yeast nutrient can provide the necessary elements for yeast health and activity. Nutrients typically contain nitrogen, vitamins, and minerals that support yeast metabolism. Follow the recommended dosage on the nutrient package to avoid over-supplementation.

5. **Oxygen Introduction**: Yeast requires oxygen for reproduction, especially during the initial stages of fermentation. If fermentation has stalled, gently swirling the fermenter can introduce a small amount of oxygen, which may help reactivate the yeast. However, this should be done cautiously, as excessive oxygen can lead to oxidation and off-flavours.

6. **Monitor Progress**: After taking corrective actions, monitor the fermentation closely. Check the specific gravity daily to observe any changes. It is essential to be patient, as it may take some time for the yeast to become active again. Once fermentation resumes, ensure that the fermentation temperature remains stable and within the optimal range.

7. **Final Considerations**: If fermentation does not restart after these interventions, it may be necessary to evaluate the entire brewing process, including sanitation practices and ingredient quality. In some cases, the batch may need to be discarded if it is deemed unsalvageable.

In conclusion, restarting a fermentation requires careful assessment and intervention. By understanding the factors that contribute to fermentation stalls and implementing the appropriate corrective measures, brewers can successfully revive their batches and achieve the desired outcomes in their brewing endeavours.