Refractometer Vs Hydrometer: Which One Should You Use To Measure The Specific Gravity Of Your Homebrew?

Oct 2021 | Last modified: November 14, 2023 | 6 min read | By David Scott

refractomer for homebrewing
triple scale hydrometer for homebrewing

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Refractometer Vs Hydrometer, that is the question.

A refractometer and a hydrometer are both useful pieces of brewing equipment to have on hand during the beer making process, and can help you brew a more consistent and better beer.

But is one better than the other, and which one should you use?

What is the Specific Gravity of Beer?

Measuring the specific gravity (SG) is one of the most important measurements you can take when brewing beer. Specific gravity is the density of a liquid, like wort or beer, compared to the density of water at a certain temperature.

For example, if you were to measure the density of pure water, you should get a specific gravity of 1.000.  Now if you were to measure the wort of a simple cream ale, before pitching the yeast, the specific gravity of should read around 1.040.

Once fermentation starts and the yeast begins feasting on the sugars in the wort, the decrease in sugars will cause the specific gravity to fall over time.

After the beer has finished fermenting, another liquid sample will be measured to obtain the final gravity (FG) of the finished beer.

How a Refractometer or Hydrometer Can Help You Brew a Better Beer

Both tools can be used to measure the specific gravity throughout the brewing process.

  • Lets you know if your specific gravity meets the specifications of your beer recipe
  • Know when fermentation has completed
  • Helps determine the mash efficiency
  • Calculates the percentage of the alcohol in your beer

What Is a Hydrometer?

A hydrometer is a simple tool that measures relative density in liquids—for instance, and in this case, the density between water and wort, and finally the finished beer.

Brewers will use a hydrometer to measure the specific gravity (SG) of the wort before fermentation begins. Samples are periodically taken and measured to monitor the fermentation process as the sugar is converted into alcohol.

How To Use a Hydrometer

Pour a sample of your liquid into the hydrometer test jar while trying to limit the amount of bubbles in the tube.

Put the hydrometer inside the tube, making sure it floats. You can give the hydrometer a spin to help get a better view of the numbers for a more accurate reading.

Hydrometers give will give the most accurate results at a specific temperature. It is always best that liquid is as close to the same temperature when reading the OG and the FG.

Using a hydrometer will require a large sample of wort or beer when measuring the specific gravity. Just make sure you don’t add the sample back into the fermenter to prevent contamination.

For a detailed look at how to measure the specific gravity of your homebrew using a hydrometer, have a look at this post here.

Calculating the ABV of Your Beer

You can calculate the ABV of the final beer by knowing the OG and the FG. You can use a calculator to come up with a final ABV, or you can use any number of online brewing calculators that will do it for you.

(OG) – (FG) x 131.25 = ABV%

You can easily find out the amount of alcohol a batch of home brew using the easy formula.

According the the cream ale recipe example above, here are the target numbers you want to reach:

Original gravity: 1.036 – 1.040

Final gravity: 1.002 – 1.006

Alcohol by volume: 1.040 – 1.006 = 0.034 x 131.25 = 4.5%

Hydrometer Pros

  • A hydrometer and test jar can cost less than $10.00
  • Easy to use
  • Calibration isn’t necessary
  • May already be included in a home brew beer kit
  • Can be used for OG and FG
  • Included in many beer making kits

Hydrometer Cons

  • Can break easily
  • Temperature of the wort can affect the accuracy
  • A testing tube or jar is needed
  • More beer is wasted

What is a Refractometer

A refractometer is another popular tool that brewers also use to measure the density and sugar content in liquids. Unlike a hydrometer, a refractometer actually measures the light refraction through the liquid.

All you need to do is place a few drops of liquid on the main prism, close the cover plate, point to a light, and look thru the eyepiece to get your reading.

Aichose Brix Refractometer
With ATC

How Does a Refractometer Work?

A refractometer measures gravity using refraction, change of movement pattern of waves as they flow different substances. For instance, when you place a spoon inside a glass filled with water, it will appear bent when you observe it from the side; This is a perfect example of refraction.

When you place your liquid sample on the refractometer, light passing through refracts at a certain angle depending on the sugar content in the sample liquid. You will read the results in Brix on the scale by looking through the refractometer’s eyepiece.

The value of Brix ranges from one to 100. You can calculate the alcohol content in your wort by multiplying the results by 0.59. alcohol content value is, however, an estimate since other factors affect fermentation. The conversion factor, therefore, ranges from 0.55 to 0.65

Using a Refractometer

Begin by calibrating the refractometer before you start using it. When done, add a few drops of the sample wort on the plate – ensure it’s at room temperature. Close the sample plate which will eliminate any bubbles and then hold the reflectometer up facing natural light.

You will read the results on the calibrated scale. In most cases, the readings are in digress Brix. If the scale is in another measurement, you can use a refractometer calculator to convert to Brix.

Refractometer Pros

  • Very simple to read
  • A few drops of wort is all it takes for a measurement.
  • Many refractometers come with temperature correction features that ensure accuracy even with small temperature differences
  • You can use just a sanitized pipette or dropper to collect a small sample from the fermenter through the airlock hole

Refractometer Cons

  • A refractometer is a little more expensive than a hydrometer
  • Requires frequent calibrations
  • Accuracy not the greatest for final gravity readings

Final Say

Although you don’t NEED a refractometer or hydrometer to brew your own beer, they are both valuable tools you should use on each brew day.

These two pieces of brewing equipment do more than just tell you how much alcohol is in your beer, they can provide you valuable information that can help you brew a better and more consistent beer.

Which one you choose is up to you, but it wouldn’t hurt to have both on hand. Many brewers like to use a refractometer for a more accurate SG reading, and then use a hydrometer to check the final gravity of the beer.

Happy Brewing!

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