Homebrew School: Understanding Floating Hydrometers

Hydrometers are a simple but incredibly important piece of equipment for professional brewers and homebrewers alike. They are used to measure the specific gravity of a fluid, which gives a reading on the density of that fluid. In this Homebrew School lesson, we'll take a look at why hydrometers are important and how to easily test their accuracy to ensure you're getting the most out of yours.

What is a Floating Hydrometer?

A floating hydrometer is a device used to measure the specific gravity (SG) of liquids. In homebrewing, this means determining the density of your wort or beer in comparison to water. This measurement helps you track the fermentation process and calculate the alcohol content of your finished beer.

How Does a Floating Hydrometer Work?

The principle behind a hydrometer is simple yet fascinating. It operates based on Archimedes' principle: a solid body submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body. 

Here's a step-by-step breakdown:

1. Preparation: Fill a test jar with your sample liquid - in this case it will be wort or beer.

2. Insertion: Gently lower the hydrometer into the liquid, ensuring it floats freely without touching the sides.

Tip: you can spin the hydrometer as you let go of it to help prevent bubbles from sticking to it and also prevent if from becoming stuck on the side of the testing vessel. Both of which can cause inaccurate readings of the hydrometer.

3. Reading: The hydrometer will eventually become stable and remain floating at a certain level. Read the specific gravity at the point where the liquid surface touches the stem of the hydrometer. Make sure to read from the bottom of the meniscus (the curved surface of the liquid) for accuracy.

Take the reading from where the surface of the liquid touches the stem of the hydrometer

Uses of a Floating Hydrometer in Homebrewing

Floating hydrometers are indispensable in homebrewing for several reasons:

• Measuring Original Gravity (OG): Before fermentation, you measure the OG of your wort. This helps you understand the potential alcohol content and also the efficiency of your brew based on the recipe used to create the wort.

• Tracking Fermentation: By taking periodic readings of the fermenting wort, you can monitor the progress of fermentation. As fermentation progresses, the gravity reading will decrease (move closer to 1.000).

As fermentation progresses, the gravity readings will move closer to 1.000

• Determining Final Gravity (FG): After fermentation, the FG reading helps you calculate the actual alcohol content and ensure fermentation is complete. This is also referred to as Terminal Gravity.
  
  The FG has been reached when the gravity reading remains unchanged for 3 days or more.

Checking the Accuracy of Your Hydrometer

Ensuring your hydrometer is accurate is crucial for reliable readings. Here’s how you can check its accuracy:

1. Visual Inspection: Check for any cracks or residues on the hydrometer. Clean it thoroughly after each use to ensure there's no debris or residual wort/beer stuck to it.

2. Calibration Test: Fill a test jar with distilled water at the temperature specified on your hydrometer (usually 60°F or 20°C). The hydrometer should read 1.000. If it doesn't, note the difference and adjust your readings accordingly.

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

3. Regular Testing: Periodically test your hydrometer with a known solution to ensure it remains accurate.

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;

• Make a note of the difference in the reading and adjust future readings accordingly

• 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.

Floating Hydrometer Alternatives

While floating hydrometers are a staple in homebrewing, there are a couple of modern alternatives that offer additional features and convenience.

Refractometers

• A refractometer can be used to measure the gravity of wort using the refraction of light against the sample liquid.

• There are analog and digital options available, but they are typically only useful for measuring wort, as the presence of alcohol in the sample skews the readings.

• We regularly use a digital refractometer for measuring the gravity of our wort during our brew days.

Our digital refractometer we use for tracking gravity throughout a brew day

• The benefit of a refractometer is the required sample size (usually a few drops) is significantly smaller than what is required for a floating hydrometer reading.

Digital Floating Hydrometers

• Digital Floating Hydrometers remain submerged in the fermenting wort throughout fermentation.

• They typically measure Specific Gravity and temperature.

• Readings are sent via Bluetooth or Wi-Fi to a cloud service, or directly to a mobile phone (depending on which digital floating hydrometer you use) for logging.

• Popular examples are the Tilt Hydrometer, RAPT Pill, iSpindel or Hydrom.

KegLand's RAPT Pill is an example of a digital floating hydrometer

• Digital Floating Hydrometers are beneficial as they require no separate samples to be taken, and give accurate, real-time information on your fermenting wort.

Conclusion

A floating hydrometer is a simple yet powerful tool in the homebrewer's arsenal. By understanding how it works and ensuring its accuracy, you can take your brewing to the next level. Happy brewing!

Feel free to share your experiences or any tips you have for using hydrometers in the comments below.

Related Articles