How to restart fermentation in wine

Fermentation is a crucial process in winemaking that converts grape juice or must into wine. It involves yeast converting the sugars in the juice into alcohol and carbon dioxide. However, sometimes the fermentation process can stall or halt altogether, leaving winemakers in a dilemma. Restarting fermentation in wine requires careful attention and managing the conditions for yeast to thrive. In this article, we will explore some effective methods to help you restart fermentation in wine.

1. Determine the reason for fermentation halt
Before attempting to restart fermentation, it is crucial to identify why the process halted in the first place. Common causes for a stalled fermentation include insufficient nutrients, low temperature, high alcohol content, or preservatives that inhibit yeast activity. Once you determine the cause, you can address it appropriately.

2. Check the sugar levels
Sugar levels play a significant role in determining the progress of fermentation. Use a hydrometer to measure the specific gravity of the wine, which indicates the sugar concentration. If the gravity is above 1.000, there are still sugars present, and fermentation hasn’t completed. On the other hand, if the gravity is closer to 1.000, the fermentation might have stopped. In such cases, restarting the process may be necessary.

3. Add yeast nutrients
If the fermentation stalled due to insufficient nutrients, adding yeast nutrients can provide the necessary elements to reignite yeast activity. Yeast nutrients such as diammonium phosphate (DAP) and yeast energizer are commercially available and can be added according to the recommended dosage. These nutrients help replenish any deficient nutrients and support yeast growth and activity.

4. Adjust the temperature
Yeast is sensitive to temperature, and low temperatures can slow down or stop the fermentation process. Ensure that the wine is stored in an environment with a temperature range of 70-85°F (21-29°C) to promote yeast activity. If necessary, you can use a heating pad or warmer to increase the temperature. Remember not to raise the temperature too quickly, as it can shock the yeast and inhibit fermentation even further.

5. Aerate the must
Aerating the must can introduce oxygen and help stimulate yeast growth. You can achieve this by stirring the wine gently or using an aeration device. Be cautious not to introduce too much oxygen, as excessive amounts can cause spoilage or oxidation. Aeration should be done a few times a day for a short duration, ensuring a steady supply of oxygen without allowing spoilage organisms to dominate.

6. Inoculate with new yeast strains
If the initial yeast strain used in fermentation couldn’t withstand the alcohol levels or other unfavorable conditions, you can consider inoculating the wine with new yeast strains. These strains, specifically designed for restarting fermentations, are more tolerant and can handle difficult conditions. Ensure that the new yeast strain matches the wine type and adjust the dosage accordingly.

7. Test for bacterial contamination
In some cases, fermentation issues can be caused by bacterial contamination. Bacteria such as lactic acid bacteria can produce undesirable off-flavors and inhibit yeast growth. Test the wine for bacterial contamination using a pH test strip or by sending a sample to a laboratory for analysis. If the wine is contaminated, appropriate sterilization methods or adding bacterial inhibitors can help eliminate the issue.

Restarting fermentation in wine requires patience and careful management. Remember to monitor the sugar levels, provide proper nutrients and temperature conditions, and ensure there are no other factors inhibiting the fermentation process. By following these steps, you increase the chances of successfully restarting the fermentation and producing a great-tasting wine.