How to use a Hydrometer: Measuring Brewing Success

November 26, 2017by Andrew Revell0

Since you’re here, chances are you’re at least curious about home brewing, even if you’re not yet a full-on fanatic! The world of beer and brewing is fascinating, but it can seem kind of overwhelming to the uninitiated. Don’t worry, we all start in the same boat. There’s a lot to learn, but the good news is that it’s the fun kind of learning.

One small but essential aspect of brewing that is often overlooked in home brewing tutorials is taking a gravity reading. Most home brew kits will supply you with a brewing hydrometer, but you’ll often be left wondering exactly what you need to do with it. At best, you’ll be advised to take a specific gravity reading at some point – but how are you supposed to know how, why and when?

Don’t worry, we’ve been there too. It took us several attempts and a lot of asking around to work out exactly to do. At Brewer’s Elite, we believe that sharing is caring. So, we’ve taken all we’ve learnt about using a hydrometer and put together this handy instructional.


What is a brewing hydrometer?

Before delving into how to use a hydrometer, it’s worth knowing what one is and why you need to use it. With a little background knowledge, it’s easier to get to grips with this handy piece of kit. In a nutshell, a hydrometer is a tool used to measure the specific gravity – or density – of any liquid, be it beer, wort, wine or water.
When dropped into wort or beer, the hydrometer will float depending on how much sugar is in suspension. Most hydrometers have at least one scale on them, which measures the ‘gravity’ of the liquid, typically ranging from 0.990 gravity points to 1.110. Normal water (at 60°F) typically has a reading of 0.000, and the more sugar a liquid contains, the higher the reading. High end brewing hydrometers will often have 2 or 3 scales, including a handy abv calculator.

Why is this useful in brewing?

As a home brewer it’s important to know how much sugar is in suspension at various stages of the brew. Wort is packed full of sugar, which results in a higher reading. Once the yeast has converted these sugars into alcohol, we can expect a lower reading.

A brewing hydrometer is most often used to ensure fermentation has been completed successfully. When you get the same reading 2 or 3 days in a row, you can be fairly certain that the yeast cannot convert any more sugars to alcohol. So, you see, it’s important to know how to use a hydrometer!

When do I need to take a reading?

Most home-brew tutorials will recommend you measure the original gravity and the final gravity. The former is taken once your wort has been cooled down after the boil, but before the yeast is pitched. The latter is taken after fermentation is complete, normally about a week after pitching the yeast. It’s recommended that you take 2 or 3 final gravity readings over the course of 2 or 3 days, to be sure fermentation really is complete.

With a simple equation, you can use the measurements to calculate the abv of your beer;

(Original Gravity – Final Gravity) X 131
(1.050 – 1.010 = 0.040) x 131 = 5.24% → 5.25% abv

If using priming sugar to carbonate your beer, add 0.5% to allow for the additional alcohol produced during the conditioning period.

While not necessarily essential, there are several other times during the brewing process when it can be useful to know how to use a hydrometer to take a reading. Be advised however, that you’ll need to cool your sample to 60°F to get an accurate reading, or use a temperature adjustment calculator.

  • After the mash and sparge you can measure the gravity of the wort in the kettle to see if you’ve hit your targets. This is also a useful way to check for mash efficiency. If you find you’re below your targets, it’s easy to add dried malt extract (DME) to the boil in order to boost the gravity.
  • Take a gravity reading of the last runnings after the sparge. In other words, the last, most diluted wort that you transfer to the kettle can also be measured. This is useful to ensure you haven’t over-sparged, resulting in tannins being extracted from the grain and causing harsh off flavors. Anything over 1.010 is fine, and if you find the reading is quite high, you may be able to transfer more than you initially thought.

How it’s done

Now that you have a better understanding of why brewers find it useful to measure the specific gravity of their wort and beer, we can take a look at how to use a hydrometer. It’s not too difficult, but there are a couple of handy tips and tricks to ensure everything runs smoothly.

There are two main methods you can use that depend on your equipment. Some brewers are happy to drop their brewing hydrometer directly into the fermenter to take a reading. While this saves beer wastage, it’s generally safer to use a hydrometer with a sample jar, in order to avoid exposing your beer to oxygen and other potential infections for too long.

Either way, it’s important that everything is clean and sanitized, especially if it’s in contact with your beer. The following steps will assume you’re using a sample jar to take your readings.

  1. Fill your sample jar with wort or beer, ensuring that the temperature of the sample is at around 60°F
    1. If your fermenter, kettle or mash tun has a tap, use this to fill your jar.
    2. Otherwise sanitize the jar and fill it up by carefully dipping it in or using a sanitized siphon.
  2. Next, hold the hydrometer at the top of the thin stem and slowly lower it into the sample.
  3. Carefully let it go and wait for it to settle.
  4. Finally take a reading. This is the part that trips a lot of people up so pay attention! The correct reading is at the same level as the surface of the liquid, not the point at which it has risen up around the stem of the hydrometer. Take a good look at eye level, keeping the sample jar on a flat surface.

It’s as easy as that, however, you might find there are a couple of issues…

Tips and tricks

In an ideal world, we would simply drop our hydrometer into the sample jar, let it settle and then take a reading. In reality, several things can obscure the reading. Fear not, here’s how you can prevent and fix most of these issues.

  • A foamy sample is always hard to read: The easiest thing to do is to overfill the sample jar, drop the hydrometer in and simply blow away any foam. The surface of the liquid should be right at the top of the sample jar.
  • The hydrometer sticks to the side of the jar: Another annoying problem, this is best rectified by spinning the hydrometer as you drop it in. It’s important that the stem isn’t touching the sides to ensure an accurate reading.
  • Bubbles obscure the reading: Gently spin the hydrometer until they are released.
  • Never return a sample! Once you’ve removed beer from the FV to take a reading, either drink it or throw it away, never put it back as you risk infecting your entire batch! This is not such a big issue before the boil.

Last call

And that’s all there is to it! Many folks believe that using a hydrometer is as easy as dropping it into a sample jar and looking at the scale. However, we think that it’s important to understand why you’re doing it and what affects the readings. When you know this, as well as a few tips and tricks, it’s easier to work out what has gone wrong when you don’t get the readings you expect.

Happy brewing and let us know if you have any hydrometer questions, or tips and tricks, in the comments section below, cheers!

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