Hydrometer and refractometer 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 beer. We are going to break down these two tools and show you how and why we use them to make the beer of your dreams.
Hydrometers and refractometers are key tools to have for homebrewers and professional brewers. They are especially helpful for new brewers to get a good sense of how fermentation works. And after fermentation to determine the final alcohol percentage as well as track fermentation progress. Those reading are called your original gravity and final gravity. Gravity is the total amount of fermentable sugars that are in your wort or beer.
As the 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 on how strong your beer will be.
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Hydrometers use the density of the liquid or how sugars the sample is. It floats up and downs based on that. There are small weighted balls inside the hydrometer that when placed in the water it floats at a specific gravity of 1.000. If the sugar is in the liquid it will float up.
Hydrometers can have various scales on them. This is probably the most common tool since it often comes in starter homebrewing kits. They are inexpensive and readily available. But they are also easy to break.
Hydrometers are extremely reliable for original and final gravity measurements plus you don’t have to worry about calibration. However, they are temperature sensitive. Most hydrometers are standardized to get an accurate measurement at 59 F. That usually means you need to chill your wort down to get a proper reading.
First, you need a decent sample of your wort and beer to get a measurement. You just fill the flask up with a sample and then drop your hydrometer in to see where it floats. The point where the top of the liquid meets the scale is your measurement. Then just toss the sample as it can cause an infection to your beer if you reintroduce it.
A refractometer measures 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. 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. This is great if you are brewing small batches or if you want to maximize your final amount.
Refractometers have an auto temperature compensation meaning you don’t have to worry about the temperature of your sample. A negative for them 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.
First, make sure it’s calibrated by placing a few drops of water on the plate and looking through the eyepiece. The measurement should read 0 or 1. If not there is usually a small screw that can be adjusted to correct. To use it just 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 where the blue area meets the white and that is your measurement. Then just repeat throughout your brewing process to find your gravity.