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February 3, 2014

Making Moonshine - How to Know when Fermentation is Finished: Part 2

This is part 2 of our article series on how to tell when fermentation is complete. Click here to check out How to Know When Fermentation is Finished - Part 1

Monitoring Fermentation - The Scientific Way

Hydrometer Final Gravity

So you followed our recommendations on the equipment distillation guide and you purchased yourself a beer hydrometer, a hydrometer test jar, and a beer sampler. You now are looking at your new equipment with a puzzled look; as it looks like nothing you've seen before. This simple guide will go through each step of the process of using a hydrometer. We will teach you how to determine the alcohol content of your mash, as well as help you know when fermentation is finished. 

The specific gravity of water is 1.000. When you take a specific gravity reading of your mash it will have a higher density compared to water because of the sugars present in mash.  During fermentation these sugars will consumed by yeast causing the density and therefore specific gravity to lower. Pre-fermentation will have the high number and the number will be the lowest at the end of fermentation.

Equipment Needed to Use a Hydrometer

  • Beer / Wine Hydrometer-  You can't use a spirit/Proof & Tralle Hydrometer for mash making.

  • Hydrometer Test Jar- You can use plastic or glass for the mash-  only use glass when you are distilling as the plastic could crack.

  • Beer Sampler- You will need a turkey baster or wine thief to take a sample of the mash for the test jar. 

The Basic Process

  • Take a post-fermentation specific gravity when you think the mash has finished fermenting.

    • If the post-fermentation gravity reading is at 1.000 or less, it is definitely done.
    • If the post-fermentation gravity reading is 1.020 or higher, you may want to wait a day or two and then take another reading
      • Keep taking readings (if needed) until the gravity stops dropping (which means that fermentation is complete).

The only true way to know if fermentation is finished is to take a gravity reading. A good rule of thumb is if the gravity of the wash has not changed over the course of 3 days then the mash is done fermenting. We know you are anxious to distill your mash but you don't want to run it prematurely as you lose out on on precious alcohol. After the airlock slows down and you are not getting much activity take a sample in your test jar and take a gravity reading. Once the gravity remains the same for 3 days in a row, the yeast is most likely done with fermentation. The specific gravity at the end of fermentation is called FG or Final Gravity. 

For information on using a proofing hydrometer check out our article "Moonshine Alcohol Content"




  • What would be too long for corn whisky mash to sit?

    Posted by Stacy on March 26, 2020
  • can you use brown sugar for your wash to make alcohol to be more like rum than vodka

    Posted by Rod Butler on December 02, 2019
  • Should the mash be stirred prior to taking a final SG?

    Posted by Rex on September 20, 2019
  • Im new to distilling however i read/watched, if your mash is real thick (corn meal is what this guy was using) add amalaze enzyme it turns the starch into a sugar is basically what I got from it.

    Posted by Bobby on June 12, 2019
  • After fermentation is complete, how long can you wait before distilling? Do you need to distill immediately or can you wait a few days?
    Thanks,David h

    Posted by David h on April 15, 2018


    Why try to stop the fermentation? you are just losing alcohol on distillation! If you absolutely cannot wait, distill the fermentation as is. The heat will pretty quickly stop the fermentation. Some side effects may be foaming or burning on base of still- due to the presence of excess sugars not fermented.

    I personally do not like solids in the fermentation (grains or fruit). If you do want this to enhance the taste, particularly in the case of fruit, rather use save some of the fruit after completing the mash to re-introduce for infusion or a second run. Grains should be discarded after no starch remains (do a iodine test on spent grains to test- please do not throw tested sample back into fermentation).

    Adding twice the amount of yeast may affect the taste of a brandy/ fruit fermentation, but should not pose a problem with a sugar wash. I suggest keep the fermentation bucket still and decant after fermentation- you may have a bit more sediment (dead yest cells) after fermentation. Remember you initial innoculation of yeast multiplies exponentially in any event, so your initial dose is really just to get things moving along/ start off.

    Likewise, event if you add too little yeast, once the fermentation kicks in and the yeast cells multiply, you should be fine. Remember to agitate/whisk the wash before you close the fermentation bucket, as this will give the yeast cells chance to procreate/multiply (which it does aerobically), when the bubbles start the yeast goes into its anaerobic phase where it eats the sugars it is done anaerobically, ie without oxygen, bubbling out CO2.

    You may have sg of 1.000 and it’s still bubbling. You are probably doing a few things right, and the end of the fermentation is near. Most of the sugars have been consumed by the yeast!

    Its is an oversimplification to say that a good fg is always 1.000. It depends on various factors, e.g. what was the initial sg, whether there are solids (etc) in the wash and whether the fermentation has stopped fermenting. Strawberries are very low in sugar, and it is for this reason probably not worth it to distill as a fruit. As in the case of kiwi, I would suggest making a sugar wash, and infusing the strawberry flavour into the alcohol afterwards.

    Posted by Abe on June 20, 2017
  • What’s a good FG for strawberry mash?

    Posted by SAm on May 05, 2017
  • there are some good questions here, how can I see what the answers are to these questions.
    John M

    Posted by JOHN m on April 15, 2017
  • Read read and read stop asking questions when answers are in the book its not rocket science i get 145 proof its easy man dont make hard for yourself read every answer is in the book

    Posted by John on July 12, 2016
  • Do you sell the Patriot built.i can’t do that. Talk to me about the so called wash.very confused. Does the fermentation happen with the grain or without. Do you reuse some of the grain or not.once again confused.

    Posted by Moe on June 01, 2016
  • What if…..the SG is at 1.000 but it’s still bubbling?

    Posted by Ken on October 18, 2015
  • I just realized i added twice as much yeast as needed. how bad is this? can it be saved?

    Posted by andrew hammer on February 10, 2015
  • How long can my mash sit after fermentation? Also my mash was really thick before I added my yeast. Is that normal. I’m new to the process and any info is greatly appriciated.

    Posted by ben takash on January 21, 2015
  • Hi, I have a sugar and molases mash of 16.2Lts added some turbo yeast on friday (exactly 72hrs ago) it started fermenting about 63hrs ago.

    Is there anything I can do to stop fermentation?
    the rate of the bubbles seems to be going down but airlock still bubbling about once every 5 seconds.

    Any help?


    Posted by GAMPsMixology on January 12, 2015
  • I just prepared a gallon of sugar wash as it’s my first time, and I wanted to keep it simple. I followed your guide on making sugar wash, but when it came to how much ingredients I needed for just 1 gallon, I scaled it back according to the guide. Because I just used needed 1 gallon, and the packet of yeast made 5, (was wine yeast) I used 1/5 of the bag. Should I of added more?

    Posted by Zack on October 31, 2014
  • All the recipes I have read say it takes 2 weeks for fermentation to complete. It’s taking my stuff like 4 weeks to complete. What am I doing wrong, if anything?

    Posted by Tom on May 19, 2014
  • Can your wash go bad after a couple of months even though it’s under anaerobic conditions? It’s been sitting there (hopefully fermenting) for almost 3 months. Sealed and air locked. Should I dump it?

    Posted by Kevin on April 08, 2014
  • What percentage of corn sugar yeast for 5 gallons

    Posted by s stone on March 06, 2014
  • Hey Kyle I’ve bought two stills from you, a five and a ten. My question is when making corn mash, and fermentation is done, do you dump every thing in the still or syphon off only the liquid? Tanks Rick

    Posted by Rick on March 04, 2014
  • All good advice but I would add DO NOT save your test samples – dump them. If they go back into the fermenter you risk introducing contamination.

    Posted by Andy on March 02, 2014

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