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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 to determine how much alcohol is in the mash. It basically measures the density of liquid in relation to water. There are 2 types of hydrometers: brewing and distilling. If you are looking to distill spirits you should own both a brewing hydrometer and a spirit hydrometer, as they are calibrated differently. You can't use a brewing hydrometer to measure the final proof of your distilled product and you can't use a spirit hydrometer while making a mash. This article will focus on the proper use of brewing hydrometers. Check this article for info on checking the final alcohol content of moonshine with a proofing hydrometer.

What do Hydrometers Measure?

Brewing hydrometers essentially measure the amount of sugar in mash and wash. The more sugar in the mash, the higher the hydrometer will float. Once the mash has finished fermentation (now called a wash) another hydrometer reading is taken to determine how much sugar the yeast ate and turned into alcohol. The greater the difference between these two numbers, the higher percentage of alcohol there is in the wash. 

There are 3 scales on most hydrometers. We're going to focus on the specific gravity scale for this article.

  1. The Brix scale which is most often used in wine-making. 
  2. The Potential alcohol scale is a rough estimate of potential alcohol for your mash.
  3. The Specific Gravity scale is used for brewing.

Determine the Original Gravity 

Using a hydrometer to determine mash original gravity

An 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 the mash and roughly indicates the percentage of alcohol that can be expected in the wash, assuming that everything goes well during fermentation.

OG varies depending on the recipe being used. For example, our favorite moonshine recipe for corn whiskey has a starting alcohol of 1.055 and only produces wash with alcohol cont in the 6% - 7.5% range.

Write down the OG in your mash 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.

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 on the hydrometer.

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

A hydrometer is calibrated to be used at 60 degrees. If you are taking a reading of your mash it is above 60 degrees you need to adjust for the actual reading. There is a great online calculator here for converting readings taken when the liquid is above or below 60 degrees.

How To Determine Alcohol Content of Wash

You need both your OG and your FG to determine your alcohol by volume (ABV). The sample we took for this article was at 1.090 and the mash fermented down to 1.010. You can  do a simple math equation to to figure it out:

  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:

1.090 minus  1.010 equals 0.08.

0.08 X 131= 10.48

Our wash is 10.48% alcohol.

What is the Ideal Starting Alcohol % for Wash?

Some recipes will produce lower starting alcohol and some will produce higher. Starting alcohol as high as 20% can be achieved if a ton of sugar is used in combination with turbo yeast. However, recipes with a starting alcohol in the 5 - 8% range will actually produce a much better tasting final product than recipes with 10% or higher starting alcohol content.

Checkout our article "How To Proof Moonshine" for information on using a proofing hydrometer

  • 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
  • The hydrometer is to measure the specifice gravity

    Posted by NME on May 23, 2014
  • how do u adjust specific gravity? I e I have a receipt that calls for a sg of 1.06, would u simply add more sugar to wash?

    Posted by tony harper on March 22, 2014
  • Cool Site. How much finished product will the government let you mafe for personal use?


    Posted by Shakey on February 26, 2014
  • Thanks for the info. I have a question, though. I use the Uncle Jesse’s recipe and method that I found of whereby you continue to remash the same grains, taking out a little of the spent corn each time and adding an equal amount of fresh along with sugar. Since there is some of the fermented wash left in the bottom of the bucket, doesn’t that affect the accuracy of the original SG reading?


    Posted by Walt on February 07, 2014
  • Do you sell hydrometers?

    Posted by local121 on February 06, 2014

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