Hydrometer vs Refractometer

Brewing small batches of beer means you want to waste as little of your beer as possible. Using a hydrometer means 100’s of mls are wasted purely to work out your ABV. Sure, you can use the sample for a taste test, but I’d much rather have a bigger volume of final product.

I thought that purchasing a refractometer was the solution to this problem, however it wasn’t that simple.

A hydrometer is very accurate when it comes to working out you ABV because of its simplicity. The buoyancy at which the hydrometer floats in you wort measures the density of your wort. Yeast eats the sugar converting the sugars into alcohol/CO2 during fermentation and the density changes. The difference in density from you OG to FG is a direct result of fermentation-conversion of sugar into alcohol. It’s a simple reliable test that only needs to take into account temperature (samples need to be around room temperature), and anything added between tests (example dry hopping certain ingredients may change the density)

However, the considerations that need to be taken into account for a refractometer are more complicated. Reading and researching about using a refractometer to work out FG is the most boring subject I have read about in regards to brewing (I understand some of you may enjoty this types of research). The considerations, calculations, differences of opinion lost my interest, it seemed the more I read, the more opinion varied and considerations increased. So, I’ll try to keep it simple. But by keeping it simple, I may overlook considerations some might consider important. In regards to this subject I’m far……very far from an expert, and I’m happy to be. Any more research would have been risking my already questionable sanity. So please read the following information as an experience I’m sharing rather than advice.

A refractometer measures the degree at which light changes angle through a liquid, called the angle of refraction. The huge benefit to small batch brewers like us is you only need a few drops of liquid to perform your test. The problem is a refractometer is meant to measure simple sugar. Wort contains complex sugars, and beer contains alcohol, both of which affect the refractometer reading. The processes chemists, beer nerds, scientists, etc have come up with to overcome these challenges in refractometer readings are varied, so here’s what I did, and my results..


1) I used this Refractometer

If you decide to buy a refractometer, make sure it has ATC (Automatic Temperature Correction) and a SG scale. The one above was the cheapest one I could find with those specs. If you’ve never used a refractometer before, its as simple as lifting the small cover plate, placing a few drops of the liquid to be tested between on the prism plate (the blue area), close the cover plate, then view the reading through the eye piece.

2) I ensured the refractometer was calibrated before every use with distilled water. I also only tested wort or beer at room temperature for consistency.

3) I measured and recorded both the OG and FG with the refractometer and hydrometer using the same sample at approximately the same time.

4) I calculated the ABV from the hydrometer readings using a standard ABV calculator on Brew Tracker.

5) I calculated the ABV from refractometer readings using the Grainfather Refractometer Correction Calculator ……refractometer correction calculators can vary slightly with their calculation depending on who designed it. I just chose this one because it’s easy to use, and allows you to enter the SG reading (some asked for BRIX only) . I used the standard variance which is pre-set at 1.04 for the correction factor. There are variations on people’s opinions to work out your Refractometer’s wort correction factor, here is a link to one such method by Brewers Friend , call me lazy but I couldn’t be bothered.

6) Below in the final column you can see the variance in results between the Hydrometer and Refractometer ABV measurement..

As you can see with a variance as little as 0.3 and as much as 0.8 the results are close enough for me to be happy to use a refractometer most of the time. There may be more considerations I needed to make (like chestnuts in the Brown Ale and the Wheat Beer fermenting in the bottle, what causes minus comparative ABV? ) and I should continue to test over a broader range of beers, but his is enough for me. If I was going to enter a beer in a competition or consider making it on larger scale, I’d still use the hydrometer to accurately work out my ABV. But beer I make for myself, friends and family, I don’t think any of us are concerned if a beer is 5%-6% knowing its somewhere within that range.

In short….

HYDROMETER- if you want to know the exact ABV of your beer, and loose 100’s of mls doing so.

REFRACTOMETER- If you would prefer the extra mls to go towards you finished product, but be off by an average of between approximately 0.3% – 0.8% of knowing you ABV.

And to prevent any backlash from the scientific society, this is just my opinion, not fact.

I should also mention that refractometers are handy test for stuck or end of fermentation. Although the gravity reading of a refractometer may not be accurate, it should be consistent in its inaccuracy and therefore a change or stabilization of gravity can be determined.

With my blogs centred around small batches of beer, this research was necessary, but I’m glad it’s over. I hope my simple and lazy approach to the subject, although flawed, has helped you decide your future methods of ABV testing.

Until next time, happy brewing!

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