How Do You Read a Hydrometer?

A hydrometer is a device used to determine the specific gravity of liquids. It works on the Archimedes principle, which states that when an object floats in water, its upward force perfectly balances gravity’s downward pull.

Utilizing a hydrometer is generally straightforward, but there are some things to consider before taking your initial readings. For instance, what scale your instrument uses and how it can be adjusted to account for changes in liquid temperature should be known beforehand.

1. Measure from the base of what’s known as “meniscus”

When reading a hydrometer, it’s essential to take your measurements at the base of what’s commonly referred to as the “meniscus.” This is an imaginary curve found on liquid surfaces.

2. Finally, submerge the hydrometer in the liquid you’re testing and wait for it to settle.

Once submerged, gently spin it around in order to shake off any air bubbles that may have formed. Make sure all bubbles have dissipated before taking your reading.

3. Finally, place the hydrometer back into its box and dry it thoroughly.

Once you’ve completed testing, it is wise to air-dry your hydrometer before placing it back into its box for storage. Doing this helps avoid moisture absorption that could interfere with accuracy of results.

4. If your scale is temperature-sensitive, calibrate it with water at the same temperature before measuring other liquids.

As previously noted, the specific gravity of liquids varies with temperature. If your measurement liquid is not at the same temperature as that which your hydrometer was calibrated for, you’ll need to adjust its readout using a temperature correction table provided by the instrument manufacturer.

5. Begin with a trial jar and your hydrometer

If you are unfamiliar with how to read a hydrometer, start with an empty 200mm long and 35mm in diameter trial jar. Fill it approximately three-quarters full so that the hydrometer floats without scraping against the bottom of the jar.

6. Before testing any fluid, such as wort or beer, make sure it’s at the ideal temperature before using your hydrometer.

7. Next, insert the hydrometer into the liquid you are testing and lower it just below where it would naturally float.

8. Once your hydrometer has settled into the liquid, you can take a reading by gently turning it until all bubbles have dissipated and the device no longer moves.

9. Convert a specific gravity reading into an alcohol percentage by referencing a table found in most hydrometer instructions.