After the primary fermentation has slowed down (after about 7 days) it’s time to check the specific gravity. What this tells us is how the density of the wine compares to that of water.
Grape juice is more dense than water. Thus before we fermented the grape juice the specific gravity was over 1.0. As the yeast converted the sugar into alcohol and carbon dioxide during fermentation, the density of the wine has been decreasing. A specific gravity less than 0.990 tells us that the primary fermentation has slowed down enough that we need to rack.
Our main concern is leaving the wine on the dead yeast, or lees, for too long. Wine is sometimes left on the decomposing yeast to impart a nutty flavor, however, you really need to know how to time this right. Left too long and the wine will start to taste like rotting yeast.
Check out this video to see all the steps involved in this part of the wine making process. The racking cane can be a bit tricky to get going so I’ve created a separate video all about how to use a racking cane. Hint, you don’t want to use your mouth to get this going!
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