Hydrometers and refractometers, they sound like tools out of a science fiction movie or chemistry classroom. But when it comes to brewing beer, they’re essential tools for measuring the fermentation activity and the final alcohol percentage of your brew.
Today, I’m going to break down these two tools and show you how and why we use them to make the beer of your dreams. I’m Trent Musho, and this is the brew show. It’s brewing tool time.
Hydrometers and refractometers are key tools to have for home brewers and pro brewers. And they’re especially helpful for new brewers to get a good sense of how fermentation works.
Both tools are used to take readings before fermentation and after fermentation to determine the final alcohol percentage, as well as track fermentation progress. Those readings are called your original gravity and final gravity.
That gravity is the total amount of fermentable sugars that are in your wort or beer. And as fermentation is underway, the sugars are eaten by the yeast. And the reading will drop to reflect that.
Without one of these tools, you’re kind of guessing at how strong your beer will be. And you’re also guessing on whether or not your beers done.
There are a few units of measurement for gravity. Specific gravity is written as a one or a zero with three decimal places.
For example, 1.056 or 0.998. The higher the number above one, the more dense with sugars the liquid is. This number is most commonly used with home brewers. And it’s what I use in my beer recipes.
Brix and Plato are another popular option that are most often used by pro brewers. Brix is represented in degrees, Brix and Plato is expressed in degrees Plato. No matter what you choose, they all do the same thing. Tell you how much fermentable sugars are available in your wort or beer.
By using a calculator, you can determine the final alcohol by volume of your beer. Most brewing software has a calculator and there’s some free ones online, but an easy equation is original gravity minus final gravity times 131.25 equals your alcohol by volume.
Let’s take a moment to talk about the differences between hydrometers and refractometers.
Differences between hydrometers & refractometers
Hydrometers use the density of the liquid or how sugary the sample is and floats up or down based on that.
There are small weighted balls inside the hydrometer that when it’s placed in water, the hydrometer floats at a specific gravity of 1.000 or zero Bx. And if there’s sugars in the liquid, it’ll float up.
Hydrometers can have various scales on them, but one of the most popular ones out there show specific gravity brix and even potential alcohol percentage. This is probably the more common tool over refractometers. Since it often comes in starter home brewing kits.
This is one of hydrometers positives, they’re inexpensive and readily available. But on the flip side of that, they’re also very easy to break. Especially if you have one made of glass. I know many brewers who have placed one on a table just to have it roll off and break releasing those tiny beads all over the floor.
Thankfully, they’re now non glass versions of hydrometers that are much more durable.
Hydrometers are extremely reliable for original and final gravity measurements. Plus you don’t have to worry about calibration between brew days. However, they are temperature sensitive.
Most hydrometers are standardized to get an accurate measurement of 59 degrees Fahrenheit. That usually means you need to chill your wort down to get a proper reading.
In some cases, you can use a slightly warmer wort to get a reading and then use a temperature conversion calculator to get the measurement. But this can be risky because using too hot of a liquid can melt the wax inside that holds the metal balls, and will impact the way your hydrometer floats, making it unusable and inaccurate.
Here’s how to use a hydrometer
First, you’ll need a decent sample of your wort or beer to get a measurement. That’s where these tall flasks come in handy. Plastic ones are definitely recommended.
You fill the flask up with a sample and then drop your hydrometer in to see where it flows. The point where the top of the liquid meets the scale is your measurement.
Then you just toss that sample as it can cause an infection to your beer if you reintroduce it. That might not be the case. If you have great cleaning and sanitizing practices, but it’s better to be safe than sorry. Especially if you’re taking a sample for final gravity.
Refractometers measure the amount of light that is bent by the liquid called refraction, to give you the concentration of sugars in the wort. They can come in different scales, but the best one to get is one that has both brix and specific gravity. Where the blue area meets the white is your measurement.
One of the biggest positives for refractometers is that you only need a small sample, a few drops of the liquid to get an instant measurement. Unlike the hydrometer that needs to be submerged. This is great if you’re brewing small batches, or if you want to maximize your final amount of beer.
It’s also super helpful on brew day since you can take measurements during the mash, boil, and throughout the day, making sure you’re on target for your original gravity. Another positive is that refractometers have an auto temperature compensation, meaning you don’t have to worry about the temperature of your sample.
A negative for refractometers is that once fermentation has started and alcohol is present, the measurement you get is not as accurate because alcohol impacts the way light is refracted, but really this is more of an annoyance than a problem since there are calculators that you can use to find out your specific gravity of beer, as long as you have the original gravity reading.
Refractometers can also be a bit more pricey than hydrometers. But these days you can find some decent options for under $40, and they’re much less likely to break compared to a glass hydrometer.
Here’s how to use a refractometer.
First, make sure it is calibrated by placing a few drops of water on the plate. And looking through the eyepiece, the measurement should read zero bricks or 1.00 on the SG scale. If not, there’s usually a small screw that can be adjusted to correct.
To use it, just to collect a few drops of your liquid and place it on the plate and close the cover. Looking through the eyepiece, which is adjustable, you will see what the blue area meets the white, and that is your measurement.
Then just repeat throughout your brewing process, making sure you’re using a sanitized spoon if you’re collecting from a fermenting beer. And if it’s been fermenting, use a refractometer calculator to find your gravity.
Some other tools you use to calculate alcohol percentage are alcohol meters and Vin-o-meters. They’re only used to tell the final alcohol percentage of the beer or wine. The price ranges for these can vary from cheap to extremely expensive.
And while it’s helpful for distillers and vintners, it’s not as helpful for the home brewer.
Some myths and common misconceptions
One misconception might be that you need a hydrometer or refractometer to brew beer. It’s actually not true. You can technically brew without one, but it might be hard to tell if you have a finished beer or stuck fermentation.
And it’s definitely hard to tell what the final ABV is. You also might be tempted to put your hydrometer in a fermentor, and while technically this might work, it can be hard to read the measurement and it’s also a contamination risk. So I would avoid doing that if you can.
Lastly, you might hear that one of these is more accurate than the other, and that’s simply not true. If you use the tool properly and take good care of it, it should give you an accurate measurement every time. In my opinion, the best way to use these two tools is in tandem.
I like to use my hydrometer on brew day to get accurate measurements. Plus there’s something satisfying about dropping it into the flask.
It also gives me a chance to taste the wort and get a sense of how the final beer might taste. Then once the beers fermenting, I use a refractometer and conversion calculator to take my final gravity readings. That way I don’t have to take a large sample to get a reading.
If you have any questions about the things we discussed today, be sure to let me know.
What other kinds of 101’s would you like to see? My goal is to make home brewing simplified so that anyone could start brewing their own beer at home.
If you’re interested in learning more about brewing, check out some of my other beginner brewing videos, and if you liked this video, give it a thumbs up.
Lead marketer, brewer, dad, and husband. Pretty much an all-round awesome guy. I’ve been homebrewing for +20 yrs, an aspiring pro-brewer and micro brewery owner!