Using a Hydrometer in the Wine Fermentation

Utilizing a hydrometer during wine fermentation is essential, as it enables you to observe how sugar is being converted to alcohol and estimate its volumetric amount in your wine. The specific gravity reading gives an estimate of this totality.

The hydrometer is one of several instruments used to measure specific gravity (refractometer and saccharometer are other examples), consisting of a transparent glass tube which floats freely in the liquid being tested and calibrated and graduated using one or more scales, including specific gravity.

Hydrometers are very easy to use; simply make sure the container you are testing in is taller than wide for accurate readings, then slowly lower a hydrometer into the liquid and note where its surface meets with its base in what is called a meniscus, this curve indicating its specific gravity.

Most hydrometers come with calibration instructions tailored specifically for their temperature range, so for accurate results it is best to read and follow these precisely as written.

As soon as you take a reading on day one, it will provide evidence that the grapes you used contained enough sugars for fermentation to take place and give an estimate of what the alcohol by volume should be. Furthermore, once fermentation has ended you should be able to tell by comparing initial SG with end SG; if there is less than one point difference then fermentation has completed and you may move onto making wine!