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Proofing and Time

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We are a start-up distillery in Richmond, VA, and have been struggling with our blending/proofing down operations. 

I Have read a lot of good advice on the ADI forums on this subject and have settled into the following sequence for proofing down our Bourbon (110pf - 90pf) and Vodka (191pf - 80pf) for bottling using 55 gallon stainless steel drums. We are using AlcoDens to calculate our batch blending and hydrometer correction readings. We are proofing down in two stages as follows:

  1. Take hydrometer reading of the source tank (270 Gallon Totes)
  2. Calculate approximately how much (by weight) of the source spirit to achieve 52 gallons at 1-2 degrees proof above target bottling-proof
  3. Weigh out the calculated amount and get an exact weight of the source spirit
  4. Take proof measurement of source batch & update calculation in AlcoDens using this proof and weight to determine the weight of distilled water to add to reach target proof.
  5. Weigh out the calculated amount of water in the bottling drum. Agitate with a pneumatic mixer and add source spirit until the calculated batch weight is reached
  6. Mix for 3-4 hours then let sit for up to 12 hours
  7. Take proof measurement of batch and update calculation in AlcoDens to determine how much additional water to add to reach bottling proof.
  8. Mix for 3-4 hours then let sit for up to 12 hours
  9. Recheck proof and repeat if needed to get bottling proof.
  10. Wait 12 hours after last check to start bottling

Now typically,am if I start bottling right after the last 12 hour wait the proof is stable at the checked proof during my bottling checks but not always. Tank is sealed and stored in the same conditioned space when not bottling but am struggling to figure out why the proof can change by as much as 2-3 degrees proof (which would not be good for bottling) by just sitting but cannot find any information on how much time it may take for the proof to settle of even if that is what is happening

Any insight from the community is welcome - although I am not trying to stir up the slow vs fast proofing debate as I realize I am proofing down using the fast method.

Thanks in advance

Bob Donovan



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An important pointer to the cause of the changing proof is whether the proof increases or decreases with time. If the proof consistently decreases on resting for 12 hours then the most likely cause is entrained air slowly escaping. The entrained or dissolved air would lower the density of the blend and would be interpreted as a higher proof by a hydrometer or EDM, and of course the proof would decrease as the air escapes.

If the proof increases over a 12 hour period that would be indicative of incomplete mixing or measurement errors. In my experience most distillers have reported that when the proof does change over a period of hours or days (as opposed to weeks or months) it does decrease and it is usually due to air.

Alcohol and water mix fairly easily so with the 3-4 hours of mixing that you have I would not suspect incomplete mixing.

There are a few stages where air can be entrained.  In your steps 3 & 4 where the spirit is being decanted from the 270 gallon tote into the weighing drum it would be very easy to entrain air if the decanting is done too vigorously. Run the spirit down the side of the weighing drum or use a hose to discharge the spirit below the level in the weighing drum.

Do you find that the proof changes from step 1 to 4?  This will tell you if you are entraining air.

In step 5 it sounds as though you are running the mixer while you are adding the spirit. Especially with the bourbon where you require relatively little water there could be a stage where the mixer’s impeller is partially submerged.  This would be a very likely source of air in the blend.  And while adding the spirit to the bottling drum the same comment made above about avoiding vigorous addition would apply.

I would recommend not running the mixer while adding either the water or the spirit, and if you are able to run it for as long as 3-4 hours you can use a low speed with gentle agitation and avoid any vortex formation or air entrainment.

Immediately after you have made the blend, is the measured proof the same as what the calculation predicted?  Again, if you find these measurements show a higher proof than expected it would indicate air inclusion at some point.

A comment that is not related to your reported problem – in step 5 you report adding the spirit to the water but common practice is to add water to spirit.  Every distiller has their own pet theory on the fast vs slow proofing debate, but in my favorite theory it is best to avoid spirit suddenly being exposed to a lot of water. This would happen if the water were to be added too fast to the spirit, but it would also happen if the spirit was added to the water.  But you have not reported taste problems or haze formation so maybe this is not worth worrying about.

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I have had discussions here before about micro bubbles of entraped air. The bubbles can get caught on the bottom of glass hydrometers, spinning the hydrometer can help get rid of them. The hand held Anton Parr snap series electronic devices certainly give false reading if small bubbles caught up. What range are your hydrometers? Are they certified? Before Anton Parr I did have a glass hydrometers with a very small crack in the glass bulb, took a while to figure out why readings kept drifting. Also floating a glass hydrometers in a narrow cylinder gives inaccurate readings. I think you are stirring for way too long. I use a paddle for a couple of minutes maximum.  What is your pneumatic stirrer? Is it a high speed propeller driven by compressed air, or do you mean using air bubbles to agitate? High speed propeller could cause cavitation and bubbles of alcohol vapour.

Following this topic.


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@PeteBI regard bubbles that form on the hydrometer/in a u-tube to be an indication that the spirit is either not mixed or not done resting after mix.

Once a cut product is homogenous (as little as 10 mins with the right mixing), you need a 15 minute or so rest for the air bubbles to get out and for readings to stabilize (I tested samples in a benchtop density meter at 1 min steps from 1-15 mins to find out the least amount of time I could wait).

You can definitely overmix product and bring its dissolved gas content out of alignment with ambient, which can cause drifting proof issues over time as the gas in the liquid returns to equilibrium.

@BobDonovan You don't specify that you are adjusting hydrometer readings for temperature or what kind of hydrometer you're using. So forgive me if you've got this covered already, but I have to mention: A certified precision hydrometer will have a range of 20 proof degrees.  If your hydrometer is 80-120 or 0-200 proof range, it's not adequate for this use case. Additionally, you need a good quality precision thermometer (also certified). You might also consider an Anton Paar EasyDens, which is a non-TTB-approved handheld device that can deliver a pretty decent proof reading using a few mLs of sample in a few seconds. This can be used to sanity-check your hydrometer measurements. If you're batching by weight and using AlcoDens correctly, you should be able to go straight from full proof to bottling proof on the first try within a very small margin of error.

Make sure AlcoDens is configured for US / 60F TTB standards: https://fx5.com/how-to-set-up-alcodens-lq-spirit-blending-calculator/

Check your scales using known good weights. Walk the 4 corners of floor scales and ensure all read within 1 division of one another.

I'm not a slow proofing advocate but I will echo meerkat's advice to slowly add water to whiskey. I like to mix with a gentle method (e.g. hand paddle) and try to use colder R/O to slow down the effect of heating that arises from cutting spirits (heat of mixing), and to minimize the chance of saponification (which is the risk when you have large unmixed blobs of water-rich/low proof liquid in your tank). It seems obvious that to some extent, nice aromas leave your spirit for good when you heat it up. 

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Too much time mixing, you do not need to mix a 55g drum volume for 6-8 hours in total.



Tank is sealed and stored in the same conditioned space when not bottling but am struggling to figure out why the proof can change by as much as 2-3 degrees proof (which would not be good for bottling) by just sitting but cannot find any information on how much time it may take for the proof to settle of even if that is what is happening

Since you mention nothing about how you are taking temperatures in the description of your process, going to suggest that perhaps you have an issue with how you are correcting proof for the temperature changes.  What hydrometers are you using?  What thermometer? 

The difference between 20 and 25c (68 and 77f) is about -2 proof.  The heat added when blending 52 gallons of alcohol and water is not going to dissipate quickly in a sealed tank. 

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Thank you all for your well-thought-out responses. Air was not on our radar as a possible culprit. Yes, we are mixing aggressively during spirit addition and we may be trapping air. Our initial thought was to try to get a homogenous blend as quickly as possible and avoid having pockets of water and the haze/sapponification issue.We are also using pneumatic pumps to transfer the spirits from storage totes to mixing drums and pumping straight into the target drum which also causes splashing etc. We also usually our take our initial proof readings soon after pumping so we definitely have high potential for entrapping air when we take our initial readings.

To help answer our measurement method & equipment, yes our hyrdometers and thermometers are certified and are within 20 degrees proof of target. We enter the observed reading and the calibration correction values for the hydrometer and thermometer into Alodens to get true proof for our blending calculation.

Thank you everyone for your inputs. We will be taking a hard look at our method for adding spirits to the tanks as it sounds like gently mixing/adding to avoid bubbles and that when successful should have an accurate proof reading fairly quickly (15-30 mins). Which is good news for our operations.


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