Bourbon Production Question

[gr8erdane]

Simply the same reason you don't pour cold water into the radiator of a hot engine I would think. When cold liquid hits hot metal the pressure of the steam is extreme and it builds up faster than it can be released. In a car, you crack the cast iron block. Just imagine what that pressure will do to a copper still.

[doubleblank]

I'll dust off my chemical engineering degree for a few moments.....as everyone knows, a distillation column is used to separate a mixture of components into two or more products. The "lighter" stuff goes overhead and the heavier "stuff" out the bottom. The column will have a temperature profile with the coldest temp at the top and hottest at the bottom. There is generally an optimum point to feed the raw mixture into the column and a corresponding temperature for that point in the column. Therefor, you heat (or cool)the feedstock to the approximate temperature of the feedpoint in the column. You don't have to get it exactly right....what is more problematic for distillations is a widely variable feedstock temperature.

Randy

[Gillman]

Just want to add a different point to what Randy is saying. Some of the lighter congeners are not desirable if you want a very light whisky or neutral spirit. Yet, because their boiling point is under or slightly over that of ethanol, they go up with the alcohol, they don't run off at the bottom. What Canadian and GNS makers do is take the first distillate (low wines) and combine it with water, reducing the proof to about 40 (20% abv) or less. Because of the addition of water, the volatility of those lighter congeners is reversed. And steam heating of the diluted feedstock will siphon off those "bad" congeners at the top of the column, and the ethanol and water mixture comes out at the bottom for entry into the rectification column and refining to a high degree of alcohol by volume (maybe 94-96% abv). Furthermore, at different levels (trays) of the third column, at different temperature points of course as Randy says, it is possible to extract more congeners if felt necessary.

These steps are not done in bourbon production, to my knowledge.

Regarding mash/wash sterilisation, it is done in Canadian practice as far as I know (Hiram Walker says on their web site they do this). I would think it may have something to do with ensuring that the wash does not deteriorate from microbial action while being held in the beer well, but I don't know for sure.

Gary

[cowdery]

Thanks, Dane. That's actually what I was looking for.

[cowdery]

Regarding mash/wash sterilisation, it is done in Canadian practice as far as I know (Hiram Walker says on their web site they do this). I would think it may have something to do with ensuring that the wash does not deteriorate from microbial action while being held in the beer well, but I don't know for sure.

I ran that by Chris and Dave, and they just shook their heads.

[Gillman]

This Friday night there is a whisky tasting event in Toronto, Forty Creek will be there although not Seagram or Hiram Walker. There will be some bourbon presence (Sazerac) and a fair amount of malt whisky. I'll ask some people about the sterilisation thing. Generally at such events one meets sales people who likely wouldn't know this stuff, but John Hall of Forty Creek may know. Anyway, I'll ask.

Gary

[doubleblank]

Hot water thrown on a hot piece of metal turns into steam FASTER than cold water does......the hot water might not crack the block though. Again, preheating the feedstock is a processing issue.....not a physics issue in this case.

Randy

[cowdery]

That's not how Dave and Chris put it. They said introducing room temperature mash into a column still heated by live steam to 165-175 degrees would cause the column to collapse on itself, and that's the reason for pre-heating.

[doubleblank]

I think what they are saying is that if one were to put room temperature feed into an operating distillation column that had previously been operating with the feedstock at 140 deg, the still could colapse onto itsef. The introduction of colder feedstock is going to reduce the temperature of the column, rapidly condensing the rising steam and alcohol vapors, which perhaps puts too much liquid loading on the trays, causing them to collapse. Its not an explosive type of event....its the exact opposite. My comment about this being a process issue is that when designing a distilation column, there will be an optimum feedpoint location and temperature by design. Apparently 140 deg +/- is it for their column.

Randy

[cowdery]

Yes, all of that. The feedpoint location is near but not exactly at the top of the column.

[Gillman]

I don't think I got this quite right, and want to try again. Extractive distillation operates on the basis that the normal volatility of certain flavor compounds in spirit can be changed. One way to do this is to mix the low wines with a lot of water, to result in about 20% abv. In the (second) distillation column, the dilute distillate is introduced at the optimum point in the column. This is the tray where the temperature will volatilise compounds whose boiling point, due to miscibility with water, has now dropped below what it was before. Under the right conditions, the compounds lift off and are removed at the top of the column. Most of the ethanol and water stay (due to having a higher boiling point than what leaves); they are drawn off from the bottom of the column. Next, these high (or higher) wines are fed into the rectification column. This brings the alcohol level smartly to about 96% abv (94% abv for grain whisky production according to John Glaser last night at Spirit of Toronto - see www.compassboxwhisky.com for John Glaser's very interesting products - which answers a question a poster had on this point. Glaser said even 2 points below 96% abv can result in significant flavor improvement)). Finally, there is the potential in some plants to remove remaining congeners at different trays (temperature points) in the third column. The resultant grain neutral spirit will contain at best only trace amounts of congeners.

I believe this to be correct but if anyone with tech knowledge wishes to elaborate or correct I encourage same, in the interest of getting accurate information on the board. I hasten to add that these processes pertain to production of high proof spirits. This is alcohol intended for use in grain whisky (Scotland, Ireland), Canadian whisky or vodka and gin - not bourbon.

Gary

[tdelling]

Your main point about there being an optimal feedpoint and temperature is

exactly right... and this is the reason to heat up the mash before putting

into the column. You could introduce room temperature mash higher up

in the column and it wouldn't collapse... but it would reduce the efficiency

of the distillation.

But I will nitpick a little bit:

> the introduction of colder feedstock is going to reduce the temperature

> of the column, rapidly condensing the rising steam and alcohol vapors,

so far so good....

> which perhaps puts too much liquid loading on the trays, causing them to

> collapse.

So you're saying that the trays can't take the weight of the liquid, and this

causes the collapse. That's probably not what's causing the collapse... there

are other, greater forces involved.

What causes the collapse is the pressure drop that happens when the gasses

condense into liquid. A partial vacuum is created... and since the external

pressure (atmospheric... about 15 pounds per square inch) is so high compared

to the internal pressure (partial vacuum), the column implodes. It's crushed

from the outside.

Google for:

atmospheric pressure demonstration

with various additions such as "video" or "55 gallon drum"

and you'll see this happen in a dramatic fashion.

Tim Dellinger

[tdelling]

Everything you said was correct... and, as a matter of fact, there are

column still designs that use as many as five separate columns in order

effeciently extract this or that with improved efficiencies and purities

in order to make industrial alcohol.

Some of the things you mentioned about how volatility changes with water

concentration are some of the subtle and delicious little enigneering

details that make column distillation so interesting and complex. The

economic importance of petroleum distillation has funded all kinds of

research in this area... far more than the liquor industry would ever

merit... so it's a pretty advanced science by now.

> I hasten to add that these processes pertain to production of high proof

> spirits. This is alcohol intended for use in grain whisky (Scotland, Ireland),

> Canadian whisky or vodka and gin - not bourbon.

It's true that bourbon only uses one column, but like most other things, it's

all in how you use the column. With a little tweaking, I'm sure that a

bourbon distillation column could be used to make vodka. Probably not

efficiently, but I bet you could.

Tim Dellinger

[doubleblank]

Maybe I assumed too much regarding their process control systems. The distillation columns I operated in a petrochemical plant had what we called high/low pressure controls....wouldn't let the pressure exceed certain limits nor go below certain limits...ie atmospheric pressure. It never occured to me that they wouldn't install a system to prevent an implosion of the stil.

Randy