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February 5, 2014

How to Use a Hydrometer

What Is a Hydrometer?

A Hydrometer is a scientific tool that we can use during brewing to determine how much alcohol was produced after a mash. It basically measures the density of liquid in relation to water.

There are 2 types of hydrometers:

A brewing hydrometer can be used to measure the specific gravity of high and medium gravity solutions. For example, you would use one of these to measure the starting and ending gravity of a wort or mash during the brew day and after fermentation.

A distilling hydrometer (also called a proofing hydrometer) is used to measure very low gravity solutions. For example you would use one of these to measure the proof of distilled spirits or the purity of fuel alcohol. 

Commercial distillers making distilled spirits should own both a brewing hydrometer and a spirit or proofing hydrometer. A person or an entity making fuel alcohol would need both hydrometers as well. Commercial brewers or home brewers will only need a brewing hydrometer.

And to clarify, a brewing hydrometer cannot be used to measure the final proof of a distilled product and a spirit hydrometer cannot be used to measure the gravity of wort or finished beer. Read this article to learn more about the proper use of brewing hydrometers. And check this article for info on how a commercial distiller would use a proofing hydrometer.

What do Brewing Hydrometers Measure?

Hydrometers essentially measure the density of liquid. So, when brewing, the initial goal is to create a sugary solution that yeast will later eat and turn into alcohol. The more sugar that ends up in liquid, the more dense it will be. And the more dense the liquid is, the higher the brewing hydrometer will float in the liquid. This is the "original gravity" reading and it tells you the "potential alcohol" of a solution. I.e., using fermentation only (and not distilling), what is the maximum amount of alcohol you would expect to end up with after the yeast have done their thing. More on this below.

After fermentation is complete, you will use a hydrometer again to measure final gravity. As in, how good of the job did the yeast actually do? How much sugar did they eat and how much alcohol did they produce. The more sugar they ate and the more alcohol they produced, the lower the hydrometer will sit in the liquid. This is called the "final gravity" reading. Again, more on this below.

What do Distilling Hydrometers Measure?

Distilling or proofing hydrometers essentially do the same thing as brewing hydrometers. They tell the distiller how much alcohol is in a solution. However, the density of spirits and fuel alcohol is so low that a brewing hydrometer would sink right to the bottom. This is because alcohol is less dense than water. And much, much less dense then water with sugar in it.

So, distilling hydrometers are said to measure alcohol by volume or "proof." Fun fact "proof" is merely ABV multiplied by 2. For example, a 40% ABV solution of alcohol would be 80 proof.

Determine the Original Gravity (For Brewing)

Using a hydrometer to determine mash original gravityAn original gravity reading is taken to determine how much sugar there is in the mash. This reading is taken BEFORE fermentation, just before yeast is added to the mash and it is aerated. As we mentioned above, the original gravity (OG) reading measures the amount of sugar in a liquid and roughly indicates the percentage of alcohol that can be expected in the wash, assuming that everything goes well during fermentation.

To use the hydrometer, fill a test tube or a tall glass with the liquid that will be fermented and drop the hydrometer in. Make sure it is floating and not resting on the bottom of the container. Hydrometers have a scale printed in or on their surface. The location at which this scale intersects the water will correspond with the specific gravity of the liquid. Taking the measurement is as easy as floating the hydrometer in the liquid and reading the number on its side.

OG varies depending on the recipe being used. For example, an India Pale Lager beer that we recently brewed had an original gravity of 1.055. If we use a yeast that ferments all the way down to 0.10, which is a common stopping point for brewers yeast, the ABV we will end up with is 5.91%

Write down the OG in your brewing journal, as you will most likely forget what it was by the time it is done fermenting, especially if you have multiple batches fermenting at the same time. Keep in mind that this reading alone does not tell you the alcohol content of your wash. It only tells you the potential alcohol content. You must take another reading (final gravity) and compare it to OG to determine the actual alcohol percentage of your wash, which we explain in the next section.

To reiterate, take an OG reading by completing the following steps:

  1. Use your beer sampler and fill your test jar almost to the top with liquid (you don't want any solids).
  2. Gently drop the beer/wine hydrometer into the test jar- you want to spin the hydrometer so it spins freely and does not stick to the side walls. You will see that the hydrometer floats on the liquid.
  3. Write down the number you see where the hydrometer intersects the liquid.

Determine the Final GravityUsing a hydrometer for moonshine mash

Final gravity measures liquid density, just like the original gravity reading does. However, if there weren't any hitches during the fermentation process, liquid density should be much lower because yeast ate all of the sugar (which increases density) and turned it into alcohol (lowering density). The difference between original and final gravity will tell you alcohol percentage of the wash.

These steps assume your mash has been fermenting for at least week and the activity in the airlock has slowed down significantly, if not stopped completely. If the airlock has not slowed down then wait a bit longer. Significant bubbling in the airlock means that the yeast is still working.

Once fermentation has finished, take a FG reading by completing the following steps:

  1. Use your beer sampler and fill your test jar almost to the top with liquid (you don't want any solids).
  2. Gently drop the beer/wine hydrometer into the test jar- you want to spin the hydrometer so it spins freely and does not stick to the side walls. You will see that the hydrometer floats on the liquid.
  3. Write down the number you see on the hydrometer- We are generally looking for a reading of around 1.010 or below. If the reading is above 1.010 let it sit for a few days and then take another reading, because the yeast might not be finished with their job yet. Keep taking samples over a few days until the reading does not change for 3 days in a row.

How To Read a Hydrometer- Temperature Correction

Most hydrometers are calibrated to be used at 60 degrees Fahrenheit. Check the instructions that came with it to be sure. If the liquid you are evaluating is above or below the calibration temp, you need to adjust for the actual reading. Again, this online calculator here offers help with the conversion

How To Determine ABV Manually

If you for some reason you can't access the online calculator we linked above, you can always calculate ABV manually. You need both the OG and the FG, mentioned above, to determine alcohol by volume (ABV). The sample we took for this article was at 1.055 and the mash fermented down to 1.010. Here's a simple math equation to determine the ABV:

  1. Subtract the Final Gravity from the Original Gravity
  2. Multiply by the difference between FG and OG by 131.

For example, the pictures used in this article were from a thin mash batch (corn whiskey that was boosted with some extra sugar). The OG was 1.090 and the the FG was 1.010. Here's how to determine the alcohol percentage of the wash:

1.055 minus  1.010 equals 0.045.

0.045 X 131.25 = 5.91

Our beer is 5.9% ABV

How to Use a Proofing Hydrometer

A proofing hydrometer works (mechanically) exactly the same way a brewing hydrometer does. However, you don't need to take a "starting gravity" reading. Simply drop a distilling hydrometer in high proof alcohol and read the number on the side. It tells you proof / ABV directly without any calculation. Though there are a couple of caveats. First, just like a brewing hydrometer, a distilling hydrometer is "temperature sensitive" so you may need to correct for temp. Also, it won't accurately measure the proof of alcohol that has had sugar added after distillation.

  • I made a cornmeal mash. It’s been fermenting for about 5 days. I took a hydrometer reading and it was at 0. This mean that there is no more sugar for the yeast to eat. Does that mean it’s ready to run?

    Posted by Leon on December 14, 2021
  • Awesome information! My husband just bought me a Chefast hydrometer and test jar set for my birthday…he said he found it on Amazon… can’t wait to use them for beer brewing and other recipes to see if they work as described… I was also thinking of using it for making kombucha… how do I use my hydrometer for brewing kombucha? Any helpful tips?

    Posted by Beer Tilly on November 12, 2018
  • Awesome site pretty much all I needed to know bookmarked!

    Posted by Troy on April 26, 2018
  • First timer here! My very first wash is a sugar wash. I figured it’s cheap easy and a good way to clean my new still running a sacrificial run through,and a chance to just familiarize myself with the basic traits of my still (pot still with thumper, eBay 8 gal stainless setup). I used 5 gallons of bottled water half distilled and half drinking, 10 pounds of cheap great value sugar and 1 tbs of common store bought bread yeast that I started with about 1 tbs of sugar and 1 tbs of regular bread yeast in 94° water. I took a gravity reading after yeast was introduced, and got 1.079. what would this come out to in a pot still with thumper after done fermenting/distilling? ABV, AND APPROX QUANTITY OF DRINKABLE STUFF? ALSO SHOULD I USE SOME FINISHED PRODUCT As A PRIMER IN THE THUMPEr FOR MY GOOD WASH run? OR JUSTi USE SOme to introduce into my good wash? Thank

    Posted by John on January 15, 2018
  • First timer here! My very first wash is a sugar wash. I figured it’s cheap easy and a good way to clean my new still running a sacrificial run through,and a chance to just familiarize myself with the basic traits of my still (pot still with thumper, eBay 8 gal stainless setup). I used 5 gallons of bottled water half distilled and half drinking, 10 pounds of cheap great value sugar and 1 tbs of common store bought bread yeast that I started with about 1 tbs of sugar and 1 tbs of regular bread yeast in 94° water. I took a gravity reading after yeast was introduced, and got 1.079. what would this come out to in a pot still with thumper after done fermenting/distilling? ABV, AND APPROX QUANTITY OF DRINKABLE STUFF? ALSO SHOULD I USE SOME FINISHED PRODUCT As A PRIMER IN THE THUMPEr FOR MY GOOD WASH run? OR JUSTi USE SOme to introduce into my good wash? Thank

    Posted by John on January 15, 2018
  • So I apologize for the caps lock. It was not intended to emphasize any point. I’m drunk and didn’t realize it. Haha. Cheers?

    Posted by Drunk on October 25, 2017
  • Do hydrometers go bad?? Mine sinks to the bottom of everything?

    Posted by TRoy on March 25, 2017
  • Just remember for every gallon of mash use 2 lbs sugar always worked for me no matter what kind of mash. Distillers yeast and yeast nutrient never fails always pull around 20 percent high yeild moonshine every time. Around 140 or higher percent.

    Posted by Norwood on February 16, 2017
  • i have 10 gallons of mash i added 12 pounds of sugar and 6 bags of dehydrated cranberries its been working 5 days i took the fruit out after 2 days but the wash was still rolling . now it seems to have slowed a bunch but has a bitter dry taste and 5% alcohol. is it ready to run? or should i add more sugar and yeast ?

    Posted by Joe on January 26, 2017
  • Cheers emmet,
    Received many thanks Kevin

    Posted by Kevin on November 14, 2016
  • Why does the hydrometer not flout after I test it once I have made the beer?

    Posted by STephen tRail on October 02, 2016
  • Hi
    I run a small 3 gallon pot still that gives me 4 mason jars of 55% from a 5gallon mash How important is it to run it through charcoal or can I get away with just cotton wool I have done 3corn mashed the tasted alright to me however I did a 100%malted barley run that tasted crap it had a kick at 60%but had a powdery barley taste would putting this through charcoal have improved it

    Posted by WIll on March 07, 2016
  • i like this

    Posted by rebelman on January 26, 2016
  • Sandy, I believe you are using a proofing hydrometer to check the mash. You’ll a mash hydrometer.

    Posted by BOb on December 14, 2015
  • have your shit at room temp when using hydrometer and when u find a proof study what ever it is to remember the bubbles how thin or thick the liquid is to have a natural understanding of waht ur drankin u no the shit be smooth and drink to much to fast best advice is to do your shit as old school as u can boiling good creek water raw ingrideants sugar for hourse power and natural yeasties or packaged enough for sugar added let work in dry clean area your amoun of yeast works it faster but yeast and fruit or grain makes compounds of more violetal and come off quicker than the stable fermented compoundes and i havnt found as many heads as lead to beleuve and its good to know your still filter you shit aas it cimes out tha worm thats enough should be clean anyway if not jus stop jus quit stupid its cimon sence think about the process of whats goin on uncle sam wont tell u and u wont listen to what every thing u read which u shouldnt have a good night

    Posted by pussygeter3000 on November 03, 2015
  • my hydrometer keeps sinking to the bottom. What’s the problem? I tried to test it at the end because I didn’t have one when I started, I even tried it in water and it still wouldn’t float.
    Thanks for any help you can give me.

    Posted by Sandy on July 18, 2015
  • Mash has been working for 10 days still bubbling but does not smell as Strong is it ready?

    Posted by Ron on June 05, 2015
  • So at a 10.48% would that be the expected yield if distilled ? So 10.48 % of a 5 gallons of wash roughly 1/2gallon. If not how do you determine how much achohol to expect out of 5gallons of wash.

    Posted by RAlphie on February 16, 2015
  • I brew my mash n my final reading. The hydrominter went straight to the bottom . I couldn’t get a reading y ?

    Posted by JErr rAt on February 15, 2015
  • Question: Your article above suggested the ideal starting alcohol % is 5-8%. If the final age is higher, can you add water to the wash to get the desired 5-8 and get the same good results? Thanks, Jess

    Posted by Jess on December 17, 2014


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