What Is A Hydrometer?

When getting into the hobby of  homebrewing it might get overwhelming because of the new words and tools that are used.  One tool that you will surely see  is called a, “Hydrometer”.  So what exactly is it?

What  A Hydrometer Is

A hydrometer is a tool that is used to measure the density of liquids relative to water.  The measurement itself is known as a specific gravity.  At some point in time someone said that the measurement of water should have the specific gravity of 1.000.  As you add more and more sugars to the mixture the gravity goes up and up.

So What?

You can really gain a lot from this reading.  In the beginning before the yeast is added you take a measurement, that is called “Original Gravity” or known as the “OG”.  This will tell you how many fermentable sugars are in the wort.  When the fermentation is complete you take another measurement, this is called, “Final Gravity” or also known as, “FG”.  The final gravity will be less than the original gravity because the yeast ate fermentable sugars in the process called fermentation.

Now What?

Having the OG and FG allows you to find out what the abv is or at least get pretty close to it.

The simplest formula that I know is this:

ABV = (Starting SG (aka OG) – Final SG (aka FG)) * 131

Example On How To Use Formula:

OG: 1.056

FG: 1.009

ABV=  (1.056-1.009) * 131

ABV = (0.047)*131

ABV = 6.2%

Side Note

When reading a hydrometer you should probably take a note of the temperature you are reading it at.   Most are calibrated for 68 degrees, so if you take your reading at 80 degrees it will be inaccurate reading.  The reason is, the hotter a mixture the thinner it will become.


Using a hydrometer is not really necessary when it comes to making beer, your beer won’t fail because of the lack of it.  But, it is helpful to take readings with a hydrometer.  Knowing what the OG and FG are is helpful for trouble shooting if your beer has any problems along the way.  It’s much like going to the doctors, no matter if it’s just a check up or if you are sick, one of the first things they will do is take your blood pressure.  It’s not the end of the world if it is a little high or a little low, but if there is something eye brow raising – then we may have some issues on our hand.

The same is with homebrewing, people will tell you what the OG and FG are suppose to be for the recipe.  Don’t expect to get it spot on every time but if you are in the ballpark you are doing good.  Also if you plan on making the same recipe again and again, it’s a good one to add into your notes.

Hope it helps ya out.



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  1. 3 Ways To Improve Your Efficiency For All-Grain | Jay's Brewing Blog - January 24, 2013

    […] What Is A Hydrometer […]

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