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Demisting test

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I know distillers here in Tasmania have used that test but I don't think they use it regularly.

I did try it when I first started but found my nose was giving me a better indication of the end of the heads. I was finishing the heads off too early with the demist test.

From my research it appears that the demisting test is not directly telling you when the heads have finished, but telling you when the heads have flushed out the tails from the previous run.

It is actually testing for leftover TAILS.

When the previous run is finished there are some long chain fatty acids and other "gunk" left on the copper in the vapour path. These are flushed out by the heads in the next run, and they cause the cloudiness when diluted with water.

The fatty acids are probably all flushed out before the heads have finished, this may be why I consider my nose a better indicator than the demisting test.

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Ah yes, the leftover tails from previous run. I should have read more closely. I suppose that might work for them if they run the same thing every time, under the exact same conditions. I guess I was originally imagining it as a test for something like ethyl acetate, which also has limited solubility in water.

Anyone use other such objective measures to start hearts cut, besides %Abv? Or is everyone relying on their on subjective sensory analyses?

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I am skeptical that the cloudiness perceived in the "demisting test" is in fact left over tails from the previous batch, and here's why:

I run malt whiskey through a German-style still with five plates, each of which is defeatable. In my second distillation, I use the plates to separate out the heads from my whiskey (a cut which, incidentally, I judge by nosing) and then defeat all five plates and continue the bulk of the run without any plates as in a pot-distillation. I run many such distillations back-to-back, and thoroughly rinse every inch of the still between batches with a very effective CIP system.

When the "demisting test" is performed on the "heads" which issue from the still prior to the defeating of the plates, the distillate is perfectly clear. It is only after the plates are defeated that the "mist" begins to form, if at all. This leads me to believe that the "mist" is actually a distinct fraction after the "heads" but before the "hearts". I have seen this "mist" carry over from batch to batch, and by excluding the "foreshots" (what I call the fraction between the heads and the hearts) but including the tails in the subsequent distillation, I have seen the "mist" completely disappear in the subsequent distillation, despite the presence of the tails and no other change in CIP procedure.

Also, I have managed to correlate the mist with short fermentations and bacterial contaminations. I suspect it is somehow related to acetaldehyde, but do not pretend to understand the mechanism. With sufficiently long and clean fermentations, I have been able to reduce the mist in my distillate to negligible amounts.

I have found the only reliable means to determine the hearts cut to be nosing. I would not recommend basing it on any other judgment. Also, I tend to repect tradition and consider any distillate that doesn't pass the demisting test to be "unpotable" even if it noses well. However, I believe that removing the "mist" would be a simple matter of filtration, if one were so inclined to include it in their spirit. Or, one could just market the spirit as "un-chill filtered" I suppose. Leave it to the Scots to find such a charming way to say "hazy".

I have been able to base my tails cut on %abv (measured as temperature), but only after study of my fermentations has allowed me to begin to enjoy very consistent washes to distill. Here also, nosing is indispensable, but %abv is a reliable guideline.

Hope my limited experience is of some help,


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You may well be right Nick. The tails causing misting may only be someones theory that someone else has put out up as fact.

All I know is I trust my nose more than the demisting test the way I have been using it

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