What is the max ABV I could redistill?

edited June 2017 in General


I'm still experimenting with my new Baby Dragon (with a 8 gallon milk can).

I'm trying to see how high of an ABV I could get out of it with multiple pass (I currently have few gallon at 85%)...

Obviously I need to make sure that there is liquid covering the element by end of the batch... but I'm wondering if there is a max ABV that I should not redistill (i.e. > 70%)

It start to be a lot of flammable liquid to boil up.

Thanks in advance


  • edited June 2017

    Yeah, sticky wicket and it's good you are concerned (means you probably won't lose your eyebrows).

    At the temperatures common in distillation, even 20% is perfectly flammable and enough vapor can be produced off even lower ABV to create an explosive atmosphere. The 30% number that floats around the intarwebs is based on an often-repeated misunderstanding. Really better that you don't set an arbitrary point and treat everything with the same level of concern. 30% is not safer than 70%, this is false.

    There might be other reasons for picking an upper bound (some times based on the same internet bs as above, maybe others that have some basis in reality).

    But, you nailed it, don't let the element get uncovered. Not that an uncovered element would necessarily flash, it probably wouldn't as long as the amount of alcohol vapor in the milk can is too rich to burn (just like a poorly tuned carb). But, if air were to get in somehow (vacuum, opening the lid) - you could be in for a bad situation if the surface of the element is above the ignition temperature of the vapor, which is VERY possible.

    If you are redistilling with a higher proof boiler charge, it generally makes no sense to collect tails. Just dump the remaining boiler contents after you are done, abracadabra - tails. Given this, you can work backwards from this to determine the appropriate remaining liquid level and any extra buffer level. And don't be greedy.

    You are going to hit a limit though, not because it's not possible to charge at 90%, or 92%, etc - it is, but because your losses are going to make it uneconomical to push further. If you lose a gallon volume trying to go from 85-87, another gallon from 87-89, another from 89-91, and so on. You get it.

  • I've read articles that say if you water your charge down to %27 it makes the spirit cleaner as that is where the alcohol/water separation is best. I don't know the science behind it.

    StillDragon Australia & New Zealand - Your StillDragon® Distributor for Australia & New Zealand

  • so would a basic idea be to add enough water to the boiler to ensure element coverage then top off with the charge?

    Seems with glassware they can redistill at because of the heating mechanism allowing almost complete evaporation.

    this had confused me previously as well.

    -air fuel mixture must be outside flammable limits - heat source must not limit complete evaporation

  • OK, so the 3rd (or 4th) distillation is not more dangerous that the 2nd one... i just really need to make sure that the element stay covered (i was more thinking for an heat transfer point of view than safety, but it's a really good point)

    Redistillation is surprisingly labor intensive (and waistfull), at some point i will need to get more plates.

  • @punkin said: I've read articles that say if you water your charge down to %27 it makes the spirit cleaner as that is where the alcohol/water separation is best. I don't know the science behind it.

    The scientific term you're looking for here is "Hydroseparation".

    The following is taken from

    "Whisky: Technology, Production and Marketing"

    Alcoholic strength of the charge of combined foreshots, feints and low wines should not exceed 30 per cent ABV; strengths in excess of this lead to blank runs, when the demisting test fails to indicate potable spirit.
    In such circumstances the demisting test protects the previously collected potable charges from an influx of non-potable spirit, which, with its high concentrations of higher fatty acid esters and long chain saturated carboxylic acids, would impart a ‘feinty’ note to the spirit. The demisting test should always be available, even if foreshots are collected on a timed basis.

    Low wines and feints receivers and chargers act as separating vessels. The last runnings of a spirit distillation contain the heavy oils or esters that are not readily soluble in water. Such oils have an affinity for alcohol, especially at164 Whisky: Technology, Production and Marketing high strength. At a strength of less than 30 per cent ABV these compounds undergo a phase separation, where the esters float on top of the aqueous layer while a small proportion are dissolved in the aqueous layer.

    If the concentration of alcohol is allowed to exceed 30 per cent ABV, these floating surface oils migrate into the higher alcoholic strength aqueous layer, being completely dissolved. This effect eventually impacts not only on the demisting test, but also on the whole spirit distillation – potable spirit cannot be collected as the charge of low wines and feints contains a disproportionate concentration of heavy oils, making it impossible to have a turbidity-free demisting test result.

    With low wines and feints charges at less than 30 per cent ABV, it is still possible to attract distillation problems. Presentation of the floating surface layer of heavy oils or higher fatty acid esters as a charge to the still (by completely emptying the contents of the charger into the still) will result in an episode when the collection of potable spirit (as determined by the demisting test) is unachievable. The whole spirit distillation system will have been contaminated by these esters, and it can take several distillations before satisfactory spirit is again obtained.

    To avoid such scenarios, when the low wines and feints appear to be approaching higher strengths (or have even reached this situation) the charge can be diluted with water, aiming for a combined strength of less than 30 per cent ABV and thus stimulating hydroseparation. The surface phase must not be allowed to enter the spirit still on charging.

    Adherence to these principles will ensure a consistent product, both on nose and analysis. The low wines and feints components reach a steady concentration state, maintaining equilibrium during subsequent distillations.



  • edited June 2017

    Boston Apothecary provides some necessary background which is missing from Whiskey Technology.

    The concept of the demisting test and blank runs are almost entirely irrelevant today as we are not running dirty stills (the louching in the heads cut being the previous runs tails), nor are we bound to use spirit safes (we can make cuts by smell and taste).

    Demisting & The Spirits Safe @ Boston Apothecary

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