Once in awhile we will get a phone call from a customer telling us their wine won’t stop fermenting. Bubbles continue to be seen in the airlock. How can this be, it should have been finished long ago?
Those of you that have made this very call, will have heard our pat answer… What is the specific gravity? If it is high, we would advise you to give it a good stir and be patient.
But if it is in the proper range, your wine might be a great weather indicator. Your wine may actually be finished fermenting, but due to changes in temperatures or barometric pressure your wine is out gassing carbon dioxide (CO2) at a rate that looks like active fermentation.
With temperature, CO2 is more soluble in a liquid the colder the temperature of the liquid. To understand this think of a can of pop. When it comes from the fridge and you open it, it barely fisses. If you were to grab it from a hot car in the summer and you opened it, it fizzes out like a volcano. The same can happen if the wine in your carboy warms up and the trapped CO2 tries to exit through the airlock. This is why we encourage you to keep you carboy temperature up when you stabilize your wine as the CO2 will be released easier, and you wine will clear properly.
Quite often, when a low pressure area marches through the area we will get a few phone calls with people telling us that their wine has started fermenting again. What happens? Under high pressure, clear skies and sunny, the higher atmospheric pressure acts to keep the CO2 in your wine. If there is a change in the weather, dropping barometric pressure, cloudy skies or rain, the pressure on your wine lessens and the trapped CO2 in your wine comes out of solution and you see bubbles in your airlock.
That is why, visual observations of your wine and it’s fermenting can not be relied upon. Using your hydrometer and tracking specific gravity is a more valuable tool to determine the progress and fermentation of your wine.