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Jun 08, 2022 View:

Loss of ABV during filtration

We are very new to this type of business, so all the help is appreciated.

When we tried to filter our second batch of alcohol we had a drop in ABV from 40%(in the blending tank) to 35.5% after the first filtration. are as the first one, and we want to understand why this happens

We are using the following:

we mix 400-450 litres per batch of ethanol and RO soft water, and blend it down to 40% then pump it up through the bottom of two SS(un-pressurized filter colums) that hold 35kgs of Macadamian nut shell carbon.

it keeps going around in series, we notice the drop in the ABV within about the first 45mins, then it stabiles for the rest of the time of filtration from 1 hour to 12 hours. What I did notice is that when we pump it the first time that it comes up through the carbon, there is about 40 litres of water pushed up, we skimmed this of both columns until we could taste and smell the "Cane" spirit.

Why would we get a drop in the ABV?

Thank you for all your help


It is not unusual to lose a very small amount of ethanol in any processing step, but that is about 10x greater drop in proof than would normally be acceptable. That said, your charcoal filter will have to saturate with ethanol until it stabilizes, and what ABV that it will stabilize at is specific to your charcoal. Once it is stabilized, you should not see much drop in ABV. General rule though is NOT to do the final adjustment of proof before filtration, but afterwards, with filtered water. So, once stabilized, try filtering at 45% or 50% ABV, then proofing down just before bottling.

If you are wondering why your charcoal might pull out so much ethanol, it depends on how hydrophobic/hydrophilic the charcoal is. More hydrophobic charcoal will tie up more ethanol as it stabilizes. Some charcoals are processed, for example with acids, to make them less hydrophobic.


I always filtered at 50% for just that reason.  I usually only got a 1-2% drop during filtration and I started with wet carbon and flushed with water.  5% seems like too much of a drop.  Start high so it can drop without getting you out of spec on bottled proof. 


Is the filter/system or carbon being rinsed with water prior to filtration?  Sounds like there is residual water in the system that isn't drained, or can't be drained.

It is customary for carbon to be rinsed with water prior to use, to reduce the level of small carbon particulate (fines).  Water logged carbon, even if not obvious, will impact proof.

From a filtration loss perspective, you might consider first running RO through the filtration system to purge.  Followed by your alcohol at a higher proof -  to compensate for the water, run RO again at the end of filtration to ensure alcohol isn't remaining in the system.  This will require some trial and error to understand what proof level you'll need to compensate for pre and post-purge.

Always target a final filtration proof slightly above bottling proof, and do your final gauge/proof after filtration to ensure hitting target proof with no issues.


Listen to this podcast (second half-ish time stamp):

Devin is a member here. 


Thank you so much for the info, this makes a lot of sense

6 hours ago, Silk City Distillers said:
Reply:18 hours ago, bluestar said:
Reply:3 hours ago, ZimDist said:

Sorry for such a simple question

when you say saturated. Do you mean leave what ever is in it after you drain it?

we started with 430litres drained it, got a net amount of 410 so still 20litres in the Colums.

so we should leave this and get the Benidorm in the next run?

Reply:On 4/24/2019 at 4:45 AM, ZimDist said:
Reply:On 4/23/2019 at 9:48 PM, ZimDist said:

Alternatively we seal and store membrane/polishing filters in the freezer to inhibit bacterial growth.  Has been working great. 

Reply:On 4/26/2019 at 3:53 AM, PeteB said:
Reply:3 hours ago, Blackheart said:

Thanks for all the help. I have got hold of PALL here, and they have a carbon filtration system that it looks like we will trial.


I will give you all feedback


DO any of you use the following:

Stage 1-Carbon Filtration : Sized at 250 LMH

Supradisc  Housing                             : WSFZ162F31UT5J - 

WSFZ Standard Accessory Kit         : GFB0157

Carbon Module                                   : PN 7007965 ;  AKS 4 300XAK4C419SP -

Stage 2Blended Product : Sized at 500 LMH

Suprak S Housing                               : SPSA100TVA – S housing   - data sheet attached 

Modules                                              : PN 5303133/S  SUPRAPAK SH 5900 SW ( Pauline may you kindly confirm if this is still available on SAP, option will be to move to lower pore size)  -