Your wine has finished fermentation and you're pondering whether to bottle it dry or perhaps back sweeten it - but is the wine ready for back sweetening? Before a wine can be back sweetened, it must be stabilized. But what is wine stabilization? Wine stabilization is the process of preventing unwanted fermentation and spoilage by inhibiting or eliminating any residual yeast or bacteria. As a home wine maker, determining if your newly fermented wine is ready for stabilization is an important skill. If you are bottling a dry wine and there are no remaining sugars, then stabilization is not required. On the other hand, if you are planning to back sweeten your wine before bottling, then stabilization is critical. Stabilization is typically done after fermentation is complete to prevent any remaining yeast from fermenting additional sugars you may add during back sweetening. Here are the steps to determine if your wine is ready for stabilization:
Signs That Fermentation is Complete
The first step for determining if your wine is ready for stabilization is to make sure the fermentation has finished. We have several tools at our disposal:
- Hydrometer Readings:
- A hydrometer measures the specific gravity (SG) of your wine, which indicates the amount of dissolved solids, which in the case of wine is primarily sugar. At the beginning of fermentation, the SG is high due to the high sugar content. Of course, this is what we expect, since the yeast will ferment those sugars to produce alcohol.
- During fermentation, yeast converts sugar to alcohol and carbon dioxide. As the sugars turn to alcohol, the density of our must decreases, which causes the SG to drop. When the SG readings are stable over a few days (typically below 1.000 for dry wines), it indicates that fermentation is complete.
- The winemaker's rule-of-thumb is to take daily readings over three consecutive days. If the readings remain consistent, fermentation is likely complete.
- Lack of Bubbles:
- Taking lots of specific gravity readings is a lot of effort. During active fermentation, you'll see bubbles rising through the wine as the yeast eats sugar and produces carbon dioxide. When fermentation is complete, bubbling will stop completely, indicating that yeast has stopped because there is no more sugar.
- Taste Test:
- A taste test can give you an idea of the wine’s dryness. If the wine tastes dry and lacks sweetness, then you'll generally conclude that most of the sugars have been converted to alcohol.
- Airlock Activity:
- An airlock allows CO2 gas to escape while preventing air from entering the fermenter. During fermentation, the airlock will bubble actively. When fermentation is complete, the bubbling will slow down or stop altogether. Monitoring airlock activity is only useful if your fermentation vessel is sealed tightly. If you have a loose-fitting lid on a bucket, for example, then the airlock may not show activity as the CO2 leaks out from beneath the lid, so you have to use a little common sense here.
- Monitor Wine Clarity:
- A wine's clarity is an important indicator in the winemaking process. A clear wine shows that most of the yeast and other particulates have settled out of suspension, indicating that the yeast cell count in the wine is low. Wine clarity is crucial for for successful wine stabilization. Even when an unfiltered wine appears clear to the naked eye, it can still harbor as many as 1000 yeast cells per milliliter. You can't see them, but they're there. While this sounds like a lot of residual yeast, a wine clear to the naked eye is generally considered ready for stabilization.
Additional Steps to Ensure Your Wine is Ready for Stabilization
- Final Hydrometer Reading:
- As mentioned above, stable hydrometer readings over a few days indicate fermentation is complete. A final reading of below 1.000 is typical for dry wines. This is a good sign. If there are no more sugars, then there are no more sugars to referment.
- Allow Extra Time:
- Even after the signs of fermentation stopping, it's beneficial to give the wine additional time to ensure that fermentation has truly finished.
- Secondary Fermentation (Optional):
- Most winemakers transfer their wine to a secondary fermenter for a few weeks (or months) to further clarify the wine and make sure fermentation is complete. This step can help in identifying any residual fermentation activity.
Stabilizing Your Wine
Okay, so you've made it through all of the above (though important) preamble. Now that you've confirmed that fermentation is complete, you can proceed with stabilization:
- Transfer Wine to a Mixing Vessel (Carboy or another Secondary Fermenter). Siphon the wine to a clean vessel, leaving behind the layer of spent yeast in the current fermenter.
- Add Potassium Metabisulfite:
- This compound helps protect the wine from oxidation and spoilage bacteria. The typical dose is 1/4 teaspoon per 5 gallons of wine. You can also use 1 Campden tablet per gallon. When using Campden tablets, be sure to crush them first and dissolve them in a small amount of water before adding to the wine.
- Add Potassium Sorbate:
- Potassium sorbate prevents any remaining yeast from fermenting additional sugars. The typical dose is 1/2 teaspoon per gallon of wine.
- Mix Thoroughly:
- Don't be lazy. Do a good job stirring both stabilizers into the wine. This should be done gently to avoid introducing oxygen into the wine.
- Wait Before Back Sweetening:
- Allow the wine to sit for a day or two after adding stabilizers before back sweetening to ensure they are fully effective.
Okay, great! You now have a stabilized wine, which sets the stage for successful back sweetening and bottling, which brings us that much closer to drinking it!