Is diluting for 2nd distillation really required?

[Alcojack]

Hi,
Most distillers I know (and me too) dilute the alcohol down to 30%-50% ABV for the 2nd and 3rd distillation. I saw this practice mentioned in some books as well, but I couldn't find the theory behind it.
If anyone here knows the reason for this I would be happy to finally understand what I'm doing...

Happy Distillation

Jack

[Swedish Pride]

alcohol is flammable above 40%, so here its advocated to dilute down to at least 40% so your boiler charge isn't flammable.
I strip down to 30% so a non issue for me

[Alcojack]

Thanks!

[Maritimer]

alcohol is flammable above 40%, so here its advocated to dilute down to at least 40% so your boiler charge isn't flammable.
I strip down to 30% so a non issue for me

Hi SP,

Note that alcohol is flammable above 40% at room temperature. Even wine is flammable when it's boiling.

M

[steelmb]

Ok, I had wanted to ask the same question myself just because I have read many times that it should be done that way but nowhere is it explained why that I have been able to find on the site. I have looked at the parent site and have done a few different google searches over the last while but have not found what I considered to be a satisfactory technical answer. I had planned on doing some more searching before asking but since I stumbled on this thread I figured I would jump on the band wagon here. Even looked up the auto ignition temperature of pure ethanol because people keep saying you must dilute it or the still will go "boom". The auto ignition temp is well above the boiling point of ethanol.

alcohol is flammable above 40%, so here its advocated to dilute down to at least 40% so your boiler charge isn't flammable.
I strip down to 30% so a non issue for me

I'm not sure I see the logic to this explanation because we all know a leaking still is an extreme hazard and that any leak can be potentially deadly. I am not trying to downplay the hazards here but the truth is that a still while operating normally has flammable vapours in the pot above the wash as well as in the column and flammable liquid in the column and in the condenser. Particularly a reflux column that is producing ethanol with a purity of 90% and above.

At the moment this is all academic for me as I am happy with single distillation in my pot still. However I am considering sometime in the future doing some redistilling to have some more neutral spirits for flavouring and making apple pie and the like. I am really curious if there is another reason other than the flammability issue. Through my searches I have run across a thread or two where people have said they have done it with no consequences.

[der wo]

I think, it was a good decicion for safety, that the moderators set a limit on abv in the boiler. If it is 30, 40 or 50% is not really important perhaps, because of course even only 5% in the boiler can get concentrated to 95% in a single reflux run and explode. But if there is a failure, it's always better to have less abv in the boiler.

Anyway, in practice there is no benefit running more than 40%, because:
-if you make neutral, it turns out better, if you dilute with water before the spirit run.
-if you make whisky, IMO it turns out better, if you strip down longer to a lower total abv than 40%.

[DAD300]

+1 der wo...

Water is the best filter. Every time you dilute it for the next distillation you remove some impurities.

Think disaster! If your boiler broke with hot 50% in it, or your condensing water suddenly stopped, your chance of a fire is far greater than at 35%.

[rad14701]

We have discussed the WHY behind diluting boiler charges to 40% ABV or lower ad nauseam... Say you have a boiler full of 40% ABV low wines and you heat it up... As the still is reaching boiling temperature there is a catastrophic failure - perhaps a split seam... "Theoretically", that 40% boiler charge could be flammable at near boiling... However, as soon as the liquid hits walls, the floor, the ceiling, it will cool to below the ignition point... With higher %ABV low wines the spirits would continue to burn where they land... 40% ABV/80 proof spirits don't burn easily... Anyone who has doubts can do their own experiments in a safe and controlled manner... I've done so and know that 40% is the maximum I will ever charge my boiler with, and usually only 35% for an extra bit of safety margin...

There may be a chart kicking around here that provides the temperature at which spirits of given %ABV will remain volatile...

[NZChris]

Some commercials do run higher abv in their high wines for the third distillation, or Jamaican style second thumper and I'm sure they have good reasons for that, but don't know what they are.

If your boiler charge is on the walls and ceiling, you are probably taking a visit to the burns unit regardless of the abv in the boiler, so make sure that cannot happen.

[Hound Dog]

If your boiler charge is on the walls and ceiling, you are probably taking a visit to the burns unit regardless of the abv in the boiler, so make sure that cannot happen.

Much wisdom is to be gleaned from this quote

Water is the best filter. Every time you dilute it for the next distillation you remove some impurities.

I believe this is the best reason to dilute.

[Squint]

on my 11 Imperial gallon keg, I always need to put in 3 gallons water so as to cover my heating element, so there is no fear of boiling dry. and therefore the spirit charge is always diluted

[Mikey-moo]

Water is the best filter. Every time you dilute it for the next distillation you remove some impurities.

+1 for that.

[NZChris]

Water is the best filter. Every time you dilute it for the next distillation you remove some impurities

That's fine if you are making neutral, but for flavored products, the "impurities" are your flavours.

[Kareltje]

on my 11 Imperial gallon keg, I always need to put in 3 gallons water so as to cover my heating element, so there is no fear of boiling dry. and therefore the spirit charge is always diluted

That is more like it.
The wish to dilute to 30 % is for reasons of taste, not for safety. So it is a valid reason, but not in this discussion.

The question is: is a load of a maximum of 40 vol-% really required for safety reasons?
I had a still that was really airtight. So the only contact of alcohol with the outside was the outlet of my condenser. I kept that at low temperature and and safe distance from my heatsource.

So for safety reasons I had no restrictions on the fill of my kettle. But there are practical reasons not to go over 40 vol-%.

1) You have to have sufficient fluid in your kettle when you are finished. So you have to have enough water in your kettle. When you distill 40 % the first drops will be about 80 %, but as your load will be exhausted you will lose more water from your kettle. You want to have enough remaining fluid in your kettle. At least: I want to have that.
2) In a pott stil a load of 40 vol-% gives a destillate of 77 vol-%, a load of 50 vol-% gives destillate of 79 vol-%. That is hardly worth the trouble: when you use a simple riser on your still you get higher percentages with less effort.

When I start my pot still with 12 vol-% I get a vapour of about 57 vol-%, so highly flammable if not explosive.
That is why I keep it enclosed in pipes and boxes and cool it as soon as possible.

So, for reasons of safety, one should not distill at all.

[skow69]

According to The Engineering Toolbox:
" The flash point of a chemical is the lowest temperature where enough fluid can evaporate to form a combustible concentration of gas."

[der wo]

In a pott stil a load of 40 vol-% gives a destillate of 77 vol-%, a load of 50 vol-% gives destillate of 79 vol-%. That is hardly worth the trouble

The cleaning from 40 to 77% is higher than from 50 to 79%. That's why diluting is better for neutrals. Not the reached % is important, but the difference from before distilling.
That's means also: When you have low wines with 50%, undiluted refluxed to 95% will taste less neutral than an only 93% refluxed from the same low wines diluted to 30%.

[Swedish Pride]

alcohol is flammable above 40%, so here its advocated to dilute down to at least 40% so your boiler charge isn't flammable.
I strip down to 30% so a non issue for me

Hi SP,

Note that alcohol is flammable above 40% at room temperature. Even wine is flammable when it's boiling.

M

good to see you back posting lad

[corene1]

I cut my low wines down before rerunning to lower the output ABV on my whisky. On my pot still with thumper a second spirit run using 40% low wines has the hearts coming out at approximately 83% which require a lot of diluting to lower to aging strength 60% . If I charge with 20% low wines my hearts come out at approximately 69% so I have to dilute less to get to my 60% oaking and aging strength which equals more flavor in the final spirit.

[MDH]

Like Corene's, my whisky enters the still at 20-25%, and the final collected spirit is about 68-71%, proofed down to 61% before aging.

The reason you should do this is simple: At too high of an alcohol content in a pot still environment, alcohol increases the volatility of heavier substances, which causes smearing in the still. At too low, the energy needed to boil the alcohol effectively also causes smearing of the fractions. There is a sweet spot which I suspect would change based on still type and stylistic preferences in whisky making, but in almost all cases in Scotland it goes in at between 19-30%.

[Kareltje]

These are more valid arguments then those on safety. Thanks for reminding me.

[NZChris]

.... but in almost all cases in Scotland it goes in at between 19-30%.

But do any of them dilute with water to get that? My understanding is that they run the low wines down to their desired abv, as many here do.

[MDH]

Here's a profile on Ardbeg, scroll down to the "Specifications" section:

http://www.wormtub.com/distilleries/dis ... ery=Ardbeg" onclick="window.open(this.href);return false;" rel="nofollow

[Mikey-moo]

Awesome link. Thanks MDH

[der wo]

Again, thank you MDH for this fantastic link.
You should open a thread "best of MDHs links".