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Jun 08, 2022 View:

Proofing Whiskey

Hey guys,

We're getting ready for our first whiskey. I'm curious to know the different methods for proofing the whiskey. Not so much about measuring the proof but how to add the water and in what quantities? All at once? Segmented? Allow whiskey to sit a while after proofing before bottling, etc? Are there any subtleties I need to be aware of? 


Thanks for your input. 


You know, the guy at Smoke Wagon made an interesting comment the other day regarding proofed whiskey...he tried a sample of something he said had just been proofed, so the "chemical reaction was still happening" and it needed to cool down. What exactly is that reaction? We have been bottling right after final proof and now I'm wondering if we are doing it all wrong....


Take a glass of whiskey and add a couple of drops of water to and and see how it opens up immediately after doing this.

That is the chemical reaction taking place he's talking about.  Generally if you can it's hard to do better than a slow addition of water to lower proof 1% per day then give it a month rest after doing this before bottling.  Of course that's not always possible so you try to do what you can.  Can you limit changes of proof to 5% per day and do a rest for 2 weeks?

If you must proof down at once try to store/rest it as long as possible before it goes in the bottle.  You'll have to figure out what works best for you and your production line but you won't go wrong doing slow proofing changes and giving spirits up to 5 weeks rest before it goes in the bottle.


I'm going to disagree with DrDistillation there and suggest that you:

- Ensure you are measuring starting proof precisely (good hydrometer, good thermometer, good lab procedure)

- Use AlcoDens software by meerkat to calculate, by weight, your cuts based on starting proof and starting weight (you can also go by volume)

- Add all the water you need to reach target proof at once and mix/agitate well for about 15 minutes

- Wait: For the next 60-90 mins the product will still be integrating (ethanol and water molecules getting together in their final interlocked configuration, spitting off heat in the process)

- Mix again for 15 minutes

- Measure proof to confirm

Taking a month to proof a cut batch is quite a luxury!

These steps are good for 50-350 gallon batches.  Smaller batches will integrate faster, larger batches will take longer & more mixing.

My mental shortcut is to think of the ethanol as if it's sand, getting dumped into water.  The "sand" needs to be completely evenly soaked with water (i.e. mixed) before you can proof it.  You can wait a month and capillary action will eventually distribute the water throughout the sand, but it wont be even (it'll be heavier at the bottom).  That's why I advocate strong mixing.  You have to force the issue, or you will wind up with a stratified tank that has substantially different proof on the bottom vs. the top, which leads to its own set of major problems (off proof product getting bottled, in particular).

I'm not a chemist but I've batched and proofed hundreds of thousands of gallons of product, personally.  These are my hard-won lessons


Slow proofing helps to prevent saponification as well as help to preserve fruity aromas that are hard to keep in whiskey.

Most people who make fine gins are well aware of proofing and resting and how it affects the botanicals, same with other spirits.

Here's some light reading.

“By allowing the molecules of the alcohol, water, and fatty acids time to bond properly, it helps preserve the fruity bouquet on the nose and intensity of aromas on the palate,” Fraley says. “We believe this process helps add a soft, silky mouthfeel to the whiskey.”

click the right arrow a few times to get to the Resting Spirits article.


Do a test yourself and pull off a couple of gallons before bottling.  Make the first your control and proof it down all at once as usual and bottle it.  With the 2nd gallon proof it down slowly over a month.  Now pull a 3rd gallon before bottling and proof that down.  Now taste all the 3 the next day and you see a difference in all three.


I've worked at two places that dilute from still strength to bottling strength in a day or two, and a place that takes 4-6 weeks. My organoleptic experience is that there is a significant quality impact to diluting brown spirits like whiskey and brandy rapidly. Taking time to do it might be a luxury, but we produce a luxury product and an extra month is negligible if it's already waited 4-6 years in barrel.   

Tank stratification was an issue at one place where the gin was proofed rapidly in a 2000 gal tank, but thorough mixing is required whether you are diluting a small amount or a large amount, fast or slow.   


I accept that the time taken for water addition can affect the taste and appearance of the product, but I doubt that this is because of any chemical reactions taking place with the water. I know through personal experience, as well as from studying the theory, that some of the cogeners are not soluble in water. If you add the water too quickly there will be zones in the mixing vessel where the cogeners are in contact with high concentrations of water and very little alcohol. The oils can form emulsions that cause haze and taste concentrations, and these emulsions are extremely difficult to get back into solution.

In his book "Distillery Operations" Payton Fireman refers to a blending operation where he weighed out the required quantity of water and then added the whiskey to it. The batch was ruined and had to be entirely re-distilled. The first whiskey to enter the water would have quickly become highly diluted, exactly as I have described above, and the oils would have come out of solution.

So I don't believe the problem is a chemical reaction that is happening over time. It seems to me to be a physical phenomenon where the oils are "squeezed" out of the alcohol and impact the appearance and taste. This physical phenomenon would be dependent not so much on the time that it takes to add the water, but rather the local rate at which it was added. Ideally the water should be added via a sparger where there will be many zones of low water concentration during mixing, rather than only one zone of much higher water concentration. The blend should be stirred during the entire operation.

If my understanding is correct, the reason for better tasting products being produced when the dilution is done over a long period would be because the rate at which the water was added was much lower than when it was done quickly. It would be interesting to hear from @JustAndy whether the water was added at a lower rate when it was done over weeks rather than over one or two days.


I totally agree with what you're saying about the local rate of water addition, but I think there is also a chemical transformation (or maybe it's physical, I am an accountant by education...) related to adding the water in small (slow) doses over a longer period of time. Each addition of water is accompanied by an infusion of oxygen from the mixing process and then this is given time to settle and normalize with the environment before the next addition. It seems to better protect the nose/perfume of the spirit. A cognac distiller told me the dilution must happen slowly enough that almost no raise in temperature occurs (for the mixture of alcohol and water). 

I certainly can't explain exactly what's going on, but my experience doing it both ways directs me going slowly, which aligns with the guidance given by enough distillers who I respect to think that it is a real phenomenon. I look at it as the difference between chopping garlic and smashing it. Scientists have proven why there is a difference in flavor (in the 90s there was a big boom in garlic research), but my great grandmother who couldn't read also knew that it happened without caring why.


Super interesting topic. Some bench trials are warranted for certain. Thanks to all who weighed in. 


So what about agitation during the blend.... Clever or not ???


Our scale has relay control to hit a set point.  Considered using a small dosing pump from our RO/DI tank connected to a solenoid for the set point.

Would be able to slowly add water, drip by drip if necessary, over the course of days or more.



I've been thinking of doing a low tech version of something similar by building a stand with a load cell and a vessel suspended top of it, so I could weigh out my proofing water into the vessel, and use gravity and a needle valve to slowly trickle water into a spirit vessel.


It would seem that slow proofing would be beneficial even with Vodka to prevent saponification.  Is this correct?


Based on what Ive read, I'm sure slow proofing vodka wouldn't hurt, but it's not as critical, because it has far fewer oils in suspention than something that is typically double pot distilled like a brandy, or has a lot of oils from botanicals like a gin.


I suppose it depends on how clean your vodka is.  The higher your purity, the more irrelevant slow proofing is going to be.

Reply:9 hours ago, Silk City Distillers said:

for any barrel aged spirits I am a huge advocate of gradual proof reduction. I try not to reduce proof more than 1 degree per day. 

The application of elevage to barrel aged spirits makes a big difference in the profile and flavor of the spirits and is worth the extra time and work

Reply:18 hours ago, captnKB said:

If you are spending several weeks proofing you don't necessarily need to take a reading if you are tracking the total water addition. But also it takes like 5 seconds to take a reading if you have a handheld density meter and perhaps 90 seconds if you have to use a hydrometer. I understand that everyones business functions differently and there are many price tiers and product niches, and slow dilution might not fit every business model. But to not use it because you are worried your employee cant do basic math? Or punch some numbers into a program? 


@adamOVDI prefer to reduce proof in the barrel as the change in proof in the barrel will extract flavors out of the barrel that will not come out at a higher proof. Overall reduction of proof slowly in the barrel yields a softer more rounded spirit. Brandy makers in europe have known this for many years but the approach has not really been given much atttention in america 


@captnKB gotcha, thought you were talking about proofing the spirts after emptying the barrel. Makes sense to proof in the barrel though, and makes slow proofing more manageable if you dont have to free up a vessel for a month or so. Thanks for the tip!


How do you account for that in TTB reporting?  Barrel storage records?


adding water to the barrel does not change the proof gallons in storage so there is no effect or change needed on your TTB reporting 


We were just talking about this were taxed on absolute alcohol if u proof down in the barrel that wont change the aboslute alcohol in barrel . Or are we wrong