Hydrometer
Use a hydrometer to measure specific gravity before, during, and after fermentation.
How to use a hydrometer
- Sanitize the test jar and hydrometer.
- Fill the jar with enough must or wine for the hydrometer to float freely.
- Spin the hydrometer gently to release bubbles clinging to the glass.
- Read the scale at the bottom of the liquid meniscus, at eye level.
- Record the temperature if your hydrometer is calibrated for a different temperature.
What the readings mean
Specific gravity (SG) compares your must to water. Water is about 1.000. Fresh grape or fruit must is often around 1.070 to 1.100. As yeast turns sugar into alcohol and carbon dioxide, SG drops.
Starting gravity (OG) is the reading before fermentation. Current gravity tells you how far fermentation has progressed. Final gravity (FG) is stable when fermentation is complete, often near 0.990 to 1.010 depending on the wine.