How to Use a Hydrometer

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A hydrometer is an essential piece of equipment for brewers and winemakers: a tube of blown, weighted glass, this device allows you to determine the specific gravity of alcohol throughout the brewing process. But although a hydrometer seems simple enough, its use requires a little bit of advanced knowledge to ensure accurate measurements.

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Instructions

Difficulty: Moderate

Step1

Use a hydrometer appropriate for your purposes: many hydrometers measure not only specific gravity, but also metrics like "potential alcohol" and sugar content. At the same time, the majority of hydrometers are calibrated to 59 degrees Fahrenheit, although this may not be a hard and fast rule. Make sure you know the calibration of your hydrometer, which will prove important later.

Step2

Clean and sanitize your any and all instruments that will come in contact with the alcohol: this includes the hydrometer, the alcoholic storage container, and measuring devices (such as siphons or turkey basters) that will be used. When all is said and done, place the storage container on a flat, even surface.

Step3

Select a sample of alcohol - your sample should contain no solid particles, which may interfere with an accurate reading. Allow your liquid to reach room temperature. Now, fill your container with just enough alcohol so that the hydrometer floats freely, without contacting the sides of the container. Do everything you can to prevent the formation of air bubbles in your sample: pour slowly, then stir gently.

Step4

Lower your hydrometer - gently, and holding it by the very top - into your sample of alcohol. Release your hydrometer while simultaneously giving it a tiny spin, to help dislodge any bubbles that may have stuck on. Make sure that the hydrometer is floating freely.

Step5

Place one finger on the top of the hydrometer's stem, and push it gently down, a few millimeters deeper into the water. Remove your finger, and let the hydrometer rise again until it reaches equilibrium. Watch the surface of the liquid: if it seems to 'crinkle,' your liquid or hydrometer may not be as clean as it needs to be.

Step6

Take a reading. The surface of the alcohol will curve into a meniscus, and the liquid may curve to meet the surface of the hydrometer. Take the measurement at the level of the liquid in the container - not, in fact, where the liquid touches the hydrometer.

Step7

With a clean thermometer, take the temperature of the alcohol, and adjust your reading from Step 6 accordingly. For this, you'll need the help of a hydrometer-temperature correction table.

Tips & Warnings

You don't need to measure your alcohol constantly: doing so too often, actually, can expose the liquid to airborne microbes, and potential contamination.
Never hold your hydrometer by the base of its stem.