This is a great tool to more conveniently measure your SG or Brix % when using your Grainfather or anytime you would have used a hydrometer. With a hydrometer you need to get a trial jar sample of wort and sometimes it is near boiling and then wait for the wort to cool before getting a reading. With the refractometer you only need to take a small sample using a spoon or pipette and only wait a few seconds before dropping a very small sample on to your refractometer. It's so much easier to take repeated readings as is often necessary during mashing.
A refractometer is an instrument that measures the refractive index of a sample. They can be used for many purposes but in brewing or winemaking they measure the sugar content of your brew and are an alternative to using a hydrometer.
Refractometers have several advantages over hydrometers such as.
- A hydrometer needs a large sample since it needs to float but only a few drops are needed for a refractometer reading.
- With a hydrometer the sample needs to be cooled to around 20C to get an accurate reading and this takes time.
- The hydrometer is generally very fragile
Depending on facilities and required sample sizes, it can take over 30 minutes to cool a sample down enough to measure the gravity with a hydrometer, and this is where refractometers really come into their own. A refractometer only needs a few drops of a sample and the most common models feature a system for Automatic Temperature Correction (ATC). This means you can take a couple of drops from the boil kettle and straight away use the refractometer to get a reading of your sugar levels. When it takes just seconds to get a reading, it is much easier to monitor how a sparge is progressing etc.
So how does this voodoo and black magic actually work? If you have ever looked from the surface of a pool or stream and tried to pick up something from under the water, you will have noticed that the object is not where it seems to be, because the light you can see is being refracted by the water. This is what makes the refractometer work, when you calibrate it, you set the 0 point using distilled water. The light passing through the sample is refracted in a specific way, and the angle the light is refracted by will changed based on the amount of sugar or alcohol in the sample.
To take a reading you open the cover plate, simply add a few drops of your sample to the sample window which is the blue area in this image. Next close the cover plate over the window, and look through the eye piece.
What you will see then will vary depending on your particular refractometer, All of them look more or less the same, but brewing refractometers come in a variety of different scales or combination of scales. Some only feature Brix, Plato or Specific Gravity and others feature combinations of these scales. This reading shows results in both Brix and SG.
There is one very important thing you need to remember with refractometers. The reading is affected by the amount of alcohol in your sample. Alcohol refracts light differently to water so once your wort has started fermenting and there is any alcohol in your sample, you will need to adjust the reading to account for the alcohol. If you do not do this then You will forever be thinking your beer has not reached its final gravity. I once had a batch of beer that was stuck at 1.018 for weeks, I pitched fresh yeast and still nothing. I had forgotten to correct for the alcohol and once I used a refractometer calculator, put in the starting and current readings, found out that the beer had indeed finished and it was under 1.010, which I was able to confirm with a hydrometer.