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January 29, 2014

Making Moonshine - How to know when fermentation is finished: Part 1

So you have 5 gallons of delicious corn mash fermenting in your basement and your Clawhammer moonshine still has been assembled and cleaned. You already read our article Bourbon, Whiskey, Vodka and Moonshine - How Much Yeast? and you added the correct amount of healthy yeast. Now you need to know how to tell when it's done fermenting.

Fermentation Variables

There are a few variables that can impact how long fermentation will take.

  1. 6.5 gallon glass carboy with corn whiskey mashThe type of yeast you use will play a large role in the amount of time it takes for a mash to ferment. Turbo yeasts will finish fermenting a lot faster than a bread yeast will.

  2. The temperature of the room the mash is fermented at will have a big impact on how long it takes to finish. A mash fermenting at 80 degrees will ferment a lot quicker than a mash fermenting at 55 degrees. 

  3. The amount of sugar is the mash will also play a big role in the amount of time needed for fermentation to finish. The more sugar in the mash the longer the fermentation will take. If you have an 8% ABV mash it is going to ferment a lot quicker than a 20% ABV mash. 

Measuring Fermentation - the Easy Way

We like to call this the "set it and forget it" method. It applies if you have your mash fermenting in a carboy or a bucket with an airlock.

Make sure 18-48 hours after you add the yeast to the carboy/bucket that you see movement in the airlock. You should see the airlock bubble a few times a minute. If you see activity in the airlock it means that the yeast is working and you're good to go. Let the mash sit for 14 days. If you still see bubbles in the airlock after 14 days let it sit for another few days, or at least until you see no bubbling for at least a minute or two. Once there is no activity in the airlock, the mash is ready to run. This is a non scientific method but has been  pretty reliable in terms of judging when fermentation has finished.

What if I don't see any activity in air lock after 18-24 hours?

If you don't see any activity after 18-24 hours make sure that the lid and airlock are tight. If both are tight then gently swirl the bucket/carboy- you just want to mix everything together. Check back after 12 hours if you still don't see any activity then add more yeast from a new yeast starter. After you add more yeast check back after 18-48 hours and you should hopefully see some activity. You should also try and keep the bread yeast happy -they seem to thrive between 74-78 degrees.

Monitoring Fermentation - the Scientific Way

The most accurate way to monitor the fermentation process when making moonshine is to use a hydrometer. Taking specific gravity measurements with a hydrometer not only lets you know that it has completely finished fermentation, it also allows you to determine the potential alcohol of your mash and the actual alcohol content of the wash. These numbers can be used for all sorts of things and we discuss all of this in our article on monitoring fermentation (the scientific way).

  • I am new to the whole home brewing community. being this is my first time to do a run, I am making 2 different 1 gallon batches. I used the same amount of pre distilled water, bread yeast, and sugar in both. the difference is one has strawberrys and pineapple the other is just sugar. my concern is the one with fruit has stopped as far as any activity (in the airlock, or any small foaming/bubbling) and the sugar one is still going strong {bubble the airlock once every 3 seconds or so}. at this point they have both been going now for 4 days. any advice or insight would be greatly appreciated.

    Posted by justin on October 13, 2016
  • Is it necessary to use thump keg

    Posted by Popav on August 07, 2016
  • to tyler yes filter for best and easy clean up
    i have s small 15 gal beer keg still with a 1 gal thumper. make several 55 gal barrels of wine last year. free fruit cant turn it down. today make a barrel of all grain mash 30 lb ground corn 5 lb barley malt 50 lb sugar. did it a little different this time 30 gal water at 200 f poured on corn and let sit stirred every 15 minutes for several hours. added another 15 gal at 150 f and 50 lb sugar once it cooled down to 150 added 1 teaspoon amylase stirring again ever 15 minutes mash thinned out a lot then added about 3 lb malt barley test on the hydrometer shows a starting of 1.06 happy with this point. will let it cool over night covered and add a gal of whiskey yeast tomorrow will see what it works to next week.
    the wines had a off flavor so i ran 4 batches and collected about 12 gal at 100 proof less the fore shot. ran this with pure water in the thumper pulled 7 gal at 155 proof and it dropped quickly on the last 2 gal to 140 and 90 on the last 2 gal 4 gal for moonshine@ 110 proof and 3 gal to make bourbon style whiskey@ 100 proof.
    starting gravity on this all grain batch show 1.06.
    wish i started doing this 20 years ago. who ever said making shine was easy must have been young man.

    Posted by tank on May 13, 2016
  • So I’m in the process of fermenting my shine. And I would like to know since I have it in five gallon buckets if I need to relieve the pressure inside by cracking the lid once a day or so. Or is there another way I should be going about this. Also my second question is when it’s time to run my mash for the final product, do I have to filter out all the corn and sugar and everything in my ferment buckets? Or do I pour everything into my still?

    Posted by TYler on May 03, 2016
  • I have a mash working now for 8 days. I used 10lbs.of sugar with 5 inches of c.o.b. feed b in a bucket . after straining my wash I added 2 qts.of pureed re – hydrated fruit, then run thru my blender with distilled water. I added 4 tbls.of turbo yeast with 4 gals.distilled water.its working good now for 8 days.it started working 10 mins.after adding air lock.should get a gal.out of my onion top copper still at 150 proff.

    Posted by Andy on April 04, 2016
  • Just started my first batch see how it goes

    Posted by phil on March 30, 2016
  • WHY WOULD MY AIRLOCK SHOW NO ACTIVITY BUT I CCANT HEAR AND SMELL IT FERMENTING

    Posted by BRYCE on March 26, 2016
  • I have a question that I hope you can help me with. I am a long time all grain Brewer and I am on my 2nd batch in my new still. Last batch my fermentation stopped at .02 OG was about .067, and I could not do anything to get it to move, so I figured I must not have achieved full conversion? Second time around I used and iodine test to validate my conversion then moved it to my conical. I hit it with a turbo yeast on Monday, now at Friday and it’s stopped at 1.025, Making me nervous… Not sure what the possible cause might be. Secondly, when I distilled my last batch I got decent yeild for quantity but a alcohol content of 40-55% about half the proof I expected ( I made all my cuts at specific temps). But I figured with the lower fermentation I would just get a lower yeild of high proof, not normal yeild with lower proof? Hopefully you can help me I am new to this so just a few questions.

    Posted by STeve on March 11, 2016
  • Dear friends, i am a newbie, my fermentation is going on with 4KG sugar and 1KG molasses in 20l water. Used 20g of bakers yest hydrated in a slice of bread, with an air lock bucket. Its been 10 days and bubbling, how many days should i wait

    Posted by Mike on March 10, 2016
  • I’m running a 5 gallon still with a thumper before the coil , is the first few ounces coming off the coil still poison or has the thumper eaten that ?

    Posted by paul on February 26, 2016
  • I’ve had this same thing happen to me before. What I did was get a packet of
    dry yeast – dissolve it in small amount of warm water with no sugar in glass
    when it has a good rise to it pour it slowly into your wash. It will start to
    eat the sugar again – let it set till done then run it as soon as it stops. your
    alcohol content should be good.

    Posted by steve on December 16, 2015
  • This question is for Jake (or anyone who knows). on the yeast, will the instant yeast still work? i unfortunately just ran across your post after i pitched flieshmann’s instant yeast. next time i’ll definitely use the active dry yeast, but i’m wondering if i should just throw this whole mash out now that i’ve pitched the instant yeast. 5 gallons of sugar wash, necessary nutrients/buffer, 10 grams of yeast.

    Posted by Beau on November 07, 2015
  • hi, i have been studing on corn whiskey/moonshine and i am preparing to make my first batch, i feel confadent that it will turn out well. i am going to order my supplies and when they arrive i will begin the process and in will get back to you with my results

    Posted by martha richardson on October 18, 2015
  • I just put a batch on its my first time and its on 32degrees c and iv got another container on room temperature. Does anyone have any advice on how long these will take?

    Posted by Thompson on October 09, 2015
  • I have a question I was cooking my mash everything was going great developed a leak shut it down fix the problem for one wasn’t able to get back to my pot for 2 days is it still OK to cook my mash it was sealed.

    Posted by Henry on September 23, 2015
  • Was Field Corn not filed

    Posted by Icobod on July 28, 2015
  • When you use corn for the mash you are using filed corn correct why doesn’t anyone use sweet corn, seems the sugar content would be higher or would it just be a waste of good eating corn LOL?

    Posted by Icobod on July 28, 2015
  • Did a mix of corn syrup and yeast a month ago, can I still run it?

    Posted by tom on June 19, 2015
  • We made 10pound sugar 1 cup yeast in a garbage can. it has sat for 6 days, starting to bubble. Not sure when we should still it? tried tonight and can taste some shine.
    How many days should we wait to still our shine?

    Posted by Crystal on June 16, 2015
  • i want to use 5 gallon buckets for mash. I have a 5 gal still pot. What do I do for the breather for fermenting? Do I need a separate type bottle or something? I have plenty of 5 gal. Buckets

    Posted by Bill on May 27, 2015


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