Monday 22 November 2021

How To Test Hydrometer Accuracy

Hydrometers are a simple but incredibly important piece of equipment for professional brewers and home brewers alike. They are used to measure the specific gravity of a fluid - which gives a reading on the density of that fluid. In the brewing world - there are two (2) main reasons to take hydrometer readings;

  1. By taking gravity readings before and after fermentation, we are able to tell the alcoholic content of the beer (by using the figures in a specific formula)
  2. By taking gravity readings over consecutive days, we are able to verify when fermentation has finished/completed (once there are no more changes to the gravity reading)
For these reasons, it's important your hydrometer is reading accurately. The process for testing their accuracy is very simple.

Fill the hydrometer test/sample tube with tap water - as close to the hydrometers calibrated temperature as possible. Our hydrometer is calibrated for 20c, so we're using water close to this temperature.

Place the hydrometer into the test/sample tube and check the reading. As per the photo below, it should be right on 1.000. Remember if the water temperature you are testing isn't close to the calibrated temperature then the reading will likely be out by a few points (or more).

Testing your hydrometer in water should give a reading close to 1.000

Most hydrometers will come with a correction scale that you can use to adjust the reading based on any temperature difference/deviation from the calibrated temperature.

Unfortunately if you're testing at the right the temperature and the reading is still out - hydrometers can't easily be recalibrated. In this case you have two (2) options;

  1. Make a note of the difference in the reading and adjust future readings accordingly
  2. Purchase a new hydrometer
Thankfully hydrometers are not particularly expensive so if you find your hydrometer isn't accurate, it's definitely worthwhile considering a replacement to ensure your gravity readings are correct.

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