How to Know When Grapes Are Fermented Enough to Make Wine

When grapes ferment, the sugar converts into a combination of alcohol and carbon dioxide with the help of yeast. Grapes are crushed into "must," and sulfites, pectic enzymes and yeast nutrient are added. After 24 hours, the yeast is added. Early on during fermentation, you will be able to see it happening. During the second stage, however -- before bottling the wine -- you won't be able to tell when it's fully fermented by sight.

Test jar
Hydrometer
Wine thief or large syringe

Instructions

- 1
  Place the test jar on a flat surface and fill it about four-fifths full with storage temperature water. For the most accurate results, the temperature should be about 60 degrees Fahrenheit.
- 2
  Dip the wine thief, which is basically a glass tube, into the must. Place your thumb over the top of the tube. Lift the wine thief out of the liquid, and hold it over the hydrometer's opening. Lift your thumb to release the liquid into the hydrometer. Alternatively, you can use a large syringe to pull the sample.
- 3
  Place the hydrometer into the water in the test jar, twisting your wrist slightly to release any air bubbles. Release the hydrometer.
- 4
  Lower your eyes to the level of the water in the test jar. Make sure that the hydrometer is not touching the sides of the jar. The hydrometer has numbers measuring specific gravity on the side, ranging from .99 at the top to 1.10 near the bottom.
- 5
  Read the number closest to the water line. If the number reads 1.09 or higher, it has fermented to 12.3% alcohol, which is enough to bottle. You may wait until it reaches a higher level if you want a stronger fermentation.

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