Author: Marshall Schott

I’d reckon most of us own (and have broken) a hydrometer or three. I received my first one in the kit I purchased at the genesis of my obsession with this hobby. It’s a fantastic tool that allows us to determine fairly accurately how much sugar is in our wort/beer based on its density (click here for a more thorough explanation), thereby providing the ability to predict the percentage of alcohol in our finished beer. Some people don’t care, which I appreciate, though can only barely relate with because I like knowing stuff like final gravity (FG) and the ABV of my beer. As helpful as they are, hydrometers do have some downsides. Since they’re made of thin glass, they are fragile and very easy to break. They also require a fairly sizable amount of wort, at least enough to fill a hydrometer jar about 75%, and the liquid has to be a specific temperature to provide the most accurate reading. After doing some research a few years ago, I discovered another tool purported to provide similarly accurate measures of specific gravity while requiring a significantly smaller sample of wort and it also had the ability to automatically correct for temperature: the refractometer.

Whereas hydrometers measure specific gravity (SG) based on the density of a liquid, refractometers determine SG using refraction of light. Basically, light is passed through a very small sample of wort and the extent to which that light refracts (bends), called the refractive index, allows us to predict the amount of sugar in our wort. I shopped around for a bit and ultimately settled on the refractometer I currently use today.

There are a ton of options out there ranging drastically in price, though all look and appear to function very similarly. My guess is they’re all likely made by the same factory in another country. I chose the one I did because, at less than $30 shipped, I felt like I could justify the purchase as an interesting experiment if it didn’t work, plus I really liked that it was dual-scale, providing measurements in both both brix and SG, no conversion needed. I was definitely skeptical this product wouldn’t be nearly as accurate as my trusty ol’ hydrometer. I’d heard of a few folks who simply couldn’t get their refractometers to match their hydrometer readings and who ultimately ended up shelving the unit for what they knew worked. But I had to give it a shot. I was certainly enticed by the very dorky idea of being able to measure the SG of my wort using a single drop at any point during the brew day.

Given my doubt, I spent probably too much time researching the pros and cons of refractometers during the 2 day period between ordering and receiving the unit. I’ve already discussed many of the pros, most of which can be summed up as “ease of use.” It was the cons, which were few and far between, that got me worried. Some people seemed to get similar readings from multiple samples of the same wort, others complained about how their refractometer samples were never aligned with their hydrometer readings, and most frequently was the concern that refractometers were terrible at providing final gravity readings. Had I made a mistake?

I received my refractometer and immediately began playing with it, first by calibrating it using a drop of pre-boiled water– either my water was slightly fermentable or my refractometer was out of whack. Using the small adjustment screwdriver that was included in the package, I made the proper adjustments so the water read 1.000 SG (0 brix). I tested it again using tap water, bottled water, and hose water, all of which resulted in the same 1.000 reading. Cool. I then measured the SG of my kids’ apple juice multiple times and it came in at 1.048 on each attempt. Watered down maple syrup, juice squeezed from a lemon, saliva– all came back with similar results on each measure. At this point, I felt confident in the consistency of the product. It was time to put it to the test on a brew day. I made a batch of wort and, for the first time, measured my pre-boil OG, something that felt like a hassle with a hydrometer. There was something exciting about knowing I’d hit the numbers predicted by BeerSmith. Once the boil was complete and the wort was chilled, I drew off a hydrometer sample to compare with the refractometer sample and found they were exactly the same. I’ve done this many times since and continue to get similar results.

As far as using a refractometer pre-fermentation, I was sold, it was so easy and accurate. The time came on that first batch to check FG, which I was convinced wouldn’t be accurate at all. I measured SG using both tools and, sure enough, they were remarkably different. While the hydrometer indicated I’d reached my target FG of 1.012, the refractometer was reading something closer to 1.024 (6.1 brix). I learned that alcohol impacts the refraction of light, hence the inaccurate reading, and that there were ways to calculate for that impact to determine a more accurate FG using a refractometer. Back to Google I went, searching for a calculator that would allow me to enter the information obtained from my refractometer and spit out a FG that matched my hydrometer. Rather quickly, I stumbled on Sean Terril’s killer website where he has a refractometer calculator that appeared to do exactly what I was looking for. His calculator requires brix, which was fine since my refractometer is dual-scale. I plugged in all the required information, pressed calculate, and the estimated FG came out to 1.0117, close enough to the 1.012 my hydrometer indicated to make me a believer. I’ve tested Sean’s calculator numerous times since and have always yielded similarly accurate results. Still, I’ve tended to stick to measuring FG with my hydrometer, mostly because I enjoy sampling the beer before packaging. If you’re concerned about FG measurements with a refractometer, know that it is absolutely possible using a good calculator.

All in all, I really like my refractometer and use it multiple times every time I brew, I’ve absolutely no regrets with this purchase. I’ve easily used it over 100 times with no issue. It has a solid feel and has proven to be quite durable. If mine were to break, I wouldn’t think twice about purchasing the same one again. Is it necessary? Not at all. But it certainly is functional and I’d argue it does increase the ease of a brew day. For those who struggle to get consistently accurate results, here’s what I’ve found seems to work pretty well:

– Calibrate the refractometer using pre-boiled or bottled water every brew day.

– Make sure your wort is mixed really well before pulling a sample, especially if you brew with extract.

– Use a brewing spoon to collect wort, allow a couple drops to fall onto the sample plate, then put the cover down and gently tap to evenly disperse the liquid.

– If the sample is from hot wort, either gently blow the plate for a few seconds or let it sit for about a minute to stabilize the temperature of the wort before taking a reading.

– Rinse and dry the refractometer immediately after every use.

That’s about it. I’m not sure I’m doing anything special, but my refractometer readings are usually spot-on with what BeerSmith predicts as well as what my hydrometer indicates. And that works for me!

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