Hydrometer? It doesn't have to be complicated.
It's a floaty thingy that bobs up and down in liquid. How hard can it be right? Well... let's add all kinds of numbers, colors, temperature, and three different types of scales (triple scale) to make things more complicated. Now you've got a tool that looks really complicated to learn. It isn't.
The two number systems are Specific Gravity(SG) and Brix.
Brix/Plato - 1 degree Brix = 1gram of sucrose in 100grams of liquid.
Specific Gravity - Density of a liquid compared to water. Water being 1.000 on the scale.
Potential Alcohol - A scale that assumes fermentation will go to 1.000.
You can see they are similar but different. One works on the ratio of sucrose to liquid, and the other works based on density when compared to water. So let's think about this. If I'm using Specific Gravity and I have 1.040, this means my solution is 4% more dense than water. If I'm using Brix and I am reading 15 degrees, this means I'm looking at a solution that has about 15 grams of sugar per 100grams of liquid. It is important to know that these are estimations. Pretty close. These estimations, depending on the hydrometer, are based on your liquid being 60 degrees F. Who sits around at that temperature? Not a lot of us. But that doesn't mean readings are worthless.
Easy right? Okay if you're not a numbers person, here's how you can make it easier.
If you're using either tool, you want to measure before you ferment and after you ferment at the same temperature. We are establishing a relative temperature. This means even if you're not at 60F in your house, you can still get an accurate reading. Just make sure if you're reading 72F before fermentation, it is reading 72 after as well. Either way we need to know the difference to calculate ABV and use the tool.
Simple Calculations:
Brix/Plato - Multiply your difference by .59. For example, before you ferment you read 11Brix. After fermentation you read 1Brix. The difference is 10 multiplied by .59 gives you 5.9%ABV.
Specific Gravity - Multiply the difference by 131.25. For example, before you ferment you read 1.070. After fermentation you read 1.010. The difference is .060 multiplied by 131.25 gives you 7.875%ABV.
Potential Alcohol - Subtract starting % with final %. For example, before you ferment you read 12%. After fermentation you read 2%. The difference is the answer with 10%.
Now that you know the scales, you understand all the numbers on the hydrometer and refractometer. There is also a small section of the hydrometer that says Potential Alcohol By Volume (ABV). This is an approximation if fermentation goes to 1. Usually fermentation goes somewhere other than 1, but it can give you a good idea of potential ABV.
I prefer to use SG because there are more points on the scale. Each line on the hydrometer in SG is 2 hundredths difference. It's easier for my head to be specific with that scale. Brix has hash marks between numbers, but SG has nice little
Tips for using your refractometer and hydrometer:
Make sure the temperature is the same when you take your readings
DON'T use a refractometer when alcohol is present. It is a great tool for measuring before fermentation, but tricky after.
Spin the hydrometer. The reason you see people do this is because bubbles sticking to the sides can throw off a reading. Spinning gets the bubbles off.
Just like above, make sure your CO2 is out of solution to get a better reading.
BUY 2 of them. When one fails, you have a backup!
There are different types of hydrometers. For most people the triple scale hydrometer is the best bet. It goes from .990 to 1.170. That's a pretty good range for homebrews. If you're into accuracy you could get a precision hydrometer. You don't get as wide of a scale, but you can easily read the differences in the points. If you want a dual purpose tool, you can grab a thermohydrometer. And, finally the easiest of all is the refractometer. One or two drops of liquid and you can see the gravity through the lens based on Snell's Law. You can't use this after fermentation though as alcohol throws it off.
Triple Scale Hydrometer (Amazon)
Precision Hydrometer (Amazon)
Thermohydrometer (Amazon)
Refractometer (Amazon)
Those are the basics. The only thing left to talk about... colors. Each hydrometer can be different, but the colors are just there to show you typical ranges for beers, wines, and distilling. Now it should be a whole lot easier for you to read a hydrometer and refractometer.
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