Using a Refractometer to Find Original Gravity

IMG_0669I recently purchased this refractometer. I’ve been wanting one ever since going to all grain brewing but the price has always pushed it to the back burner. They are $80 at my local homebrew shop and the big mail order places have them a little cheaper, but with shipping it’s not much different. A few weeks ago, though I found this one for around $20. I mentioned Homebrew Finds, but I will again because that is where I saw it and I’m very glad I did.

A refractometer is a tool used to measure the amount of sugar in a liquid solution, something that is often done by homebrewers with a hydrometer. The two instruments work in very different ways. A hydrometer is allowed to float in the liquid. It is calibrated and marked to float at a certain level when in pure water. The denser the water is, the more sugar is in it and the higher the hydrometer will float.


The refractometers that brewers use, there are other more advanced versions used in laboratories for other testing, measure the sugar content of a few drops of liquid over on a lens. Holding the refractometer up to the light and looking in the viewfinder, you can see a chart which shows the sugar content of the sample in Brix. It is measured by reflecting light through the sample and measuring how much the light is bent. Brix is not a scale most homebrewers use, but it can be converted to specific gravity fairly easily.


If you are just looking for a rough idea of the gravity, you can simply multiply your Brix measurement by four. Ten Brix is roughly 1.040 specific gravity. This is not exact and gets less accurate as the gravity is raised. To get an exact conversion there is a slightly more complicated equation. You can find it easily online, or use software to convert it for you.

Unfortunately, refractometer’s do not work the same on liquid that contains alcohol. There are more complicated calculations that you can make to find your final gravity and even find the alcohol content if you don’t know your original gravity. I just got my refractometer and don’t know nearly enough about how this works yet. I hope to learn more and use my refractometer for more in the future, but for now I just want it to check gravity throughout brew day.

With this extra complication, why use a refractometer instead of a hydrometer for your original gravity readings? There are two reasons that make it very handy for all grain brewers. The first and most obvious is that it only takes a few drops of wort. To measure gravity with a hydrometer, you have to fill a flask for it to float in which is usually about a cup of beer you will be losing.

The other reason, which is the main thing that made me want a refractometer is that the wort can be measured right out of the kettle without having to cool down to the appropriate temperature. Within thirty seconds of taking the wort, you can have an accurate gravity reading. This is crucial for all grain brewers during mashing and sparging. Since going all grain, I’ve basically been flying blind during the boil. I normally take a hydrometer sample before starting the boil, but by the time it gets to the right temperature, I’ve already started adding hops.

More experienced brewers may be able to trust their system and skills enough to assume they hit their expected efficiency, but I’m still working on this and, as with my recent batch of Mount Hoodie
, sometimes something goes wrong. If I had this tool on that brew day, I would have known before starting the boil that I didn’t get full conversion and could have either extended the mash to try to convert more, cut my batch size down or at least cut down on my hops to compensate for the lower gravity and keep from throwing the beer off balance.

I’ve only gotten to use my refractometer for two brew days so far, but it has been extremely helpful. It was especially appreciated yesterday while brewing Table Cat as I was returning to the Brew in a Bag method which I hadn’t done in a while. I was not sure what kind of efficiency to expect, but with the refractometer to test along the way for conversion, it was a very smooth brew day.


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