How to Use a Hydrometer

Common Hydrometer

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As more and more sugar gets converted to ethanol (which is less dense than water), the hydrometer sinks further and further into the fluid. Water has a specific gravity of 1.0. Beers usually have a final gravity of between 1.005 and 1.015 (although there are many that finish higher). The higher that the beer's finishing gravity, the more sugars are left in the beer and the sweeter it will taste. Beers that finish around 1.005 will be perceived as being "dry" because they have very little residual sugars left. This is just one tool you can use. Use it to find problems in mashing, boiling, and fermentation.

Worts that mash-out with too low or too high of a specific gravity will need to be adjusted (or you can choose to leave them alone). You may need to adjust your hop schedule based on the new pre-boil gravity to obtain the same levels of bitterness as the recipe. Too high of a pre-boil gravity can be adjusted with more brewing water. You can adjust your post boil gravity in the same manner, adding extract for low gravities and water for high gravities.

And finally, you will be able chart the progress of your fermentation by watching the specific gravities of the beer as it ferments. You will be able to detect stuck fermentations by a SG that does not finish low enough and does not decrease at all over time. To remedy a stuck fermentation, you can move the beer to a warmer environment, get the yeast back into suspension, pitch more yeast, add more oxygen, or any combination of the above. You can also adjust these things to get a beer to finish attenuating those last few points. It will make a difference in the flavor and mouthfeel of your beer.

How to Read Your Beer Hydrometer

Reading the Meniscus on a HydrometerHow to Read the Meniscus on a Hydrometer

Pour your sample into a clear cylinder that is dry or has been well rinsed with your sample

  1. Be sure your sample is well mixed prior to testing
  2. Immerse the hydrometer in the solution to a point slightly below the point where it naturally floats. Spin it to free it from any clinging bubbles which might buoy the instrument. Make sure the liquid is still.
  3. Measure the temperature of the sample. Ideally, the sample's temperature will be equal to the calibration temperature of the hydrometer, generally 60°F. If you cannot avoid temperature differences, use the chart below to adjust the reading.
  4. Take your reading at eye level. Read at the point where the surface of the liquid crosses the hydrometer, at the bottom of the meniscus (see the example above).

Download this temperature correction table from Thermco Products, Inc. in .pdf form.

How to Calibrate Your Beer Hydrometer

Calibrate by measuring distilled water at the calibration temperature (usually 60° or 68°F) and apply the correction factor to all readings. When reading specific gravities at temperatures other than the calibration temperature, such as a post-boil gravity at 120°F, use the chart below:

Video: by NorthernBrewerTV on YouTube

Hydrometer Temperature Correction Table

Degrees Fahrenheit Adjustment to Reading
40 Subtract .002
50 Subtract .001
60 CORRECT
70 Add .001
80 Add .002
90 Add .004
100 Add .005
110 Add .007
120 Add .008
130 Add .010
140 Add .013
150 Add .015


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