How do you tell if you have a stuck fermentation?

Answered by James Smith

As an experienced sommelier and brewer, I can provide you with detailed insights on how to determine if you have a stuck fermentation. It's important to approach this issue methodically to ensure accurate assessment.

1. Taste the : The first step is to taste the wine. If it has any hint of sweetness, even a slight sweetness, it indicates that there is still sugar present in the wine. During fermentation, consumes sugar and converts it into . Therefore, if there is residual sweetness, it suggests that fermentation might not have completed.

2. Monitor specific gravity: Another way to determine if fermentation is stuck is by measuring the specific gravity of the wine using a hydrometer or refractometer. Take initial readings before fermentation starts and compare them to the current readings. If the specific gravity remains unchanged for an extended period, it suggests that fermentation has stalled.

3. Observe airlock activity: During active fermentation, you would typically see bubbles or hear the sound of gas escaping through the airlock. If there is no airlock activity for an extended period, it could indicate a stuck fermentation. However, keep in mind that this method is not foolproof as some fermentations can proceed without noticeable airlock activity.

4. Check for suspended yeast: Examine the wine for any suspended yeast particles. If you notice a significant amount of yeast settled at the bottom of the fermenter, it could indicate that the yeast has stopped working and fermentation is stuck. However, it's essential to differentiate between normal yeast sediment and a large amount that suggests fermentation issues.

5. Measure residual sugar: Using a wine testing kit or taking a sample to a wine lab, you can measure the residual sugar content in the wine. If the sugar levels are higher than expected or not close to zero, it suggests that fermentation has not completed. This method provides an accurate quantitative measurement of residual sugar.

6. Conduct a fermentation restart test: If you suspect a stuck fermentation, you can perform a fermentation restart test. Take a small sample of the wine and add a small amount of active yeast and nutrient. Place the sample in a separate container and monitor it for signs of fermentation over a few days. If this sample shows signs of fermentation, it confirms that the main fermentation is indeed stuck.

7. Seek professional advice: If you have tried various methods to determine if your fermentation is stuck and are still uncertain, it may be best to consult a professional winemaker or brewer. They can provide expert guidance based on their experience and help troubleshoot the issue.

Remember, each fermentation can have unique characteristics, and these methods should be used collectively to confirm if your fermentation is stuck. It's also important to identify the underlying cause of the stuck fermentation, which could include factors such as low nutrient levels, improper yeast selection, temperature fluctuations, or high levels of alcohol or sulfur dioxide.