Air, Angels, and Thoughts.

[StraightBoston]

This sounds like a job for etohchem! (Quick! Shine the Angel-Signal into the Frankfort night sky!)

I had missed the discussion of the Diageo clingwrap -- a fascinating idea! I wonder if it could be applied (so to speak) in moderation, leaving it on or off for a certain period at the beginning or tail end of maturation to allow the benefits of evaporation and air introduction while maximizing yield.

[pepcycle]

Air?
I'm not worried about air in barrels. Not as long as bourbon vapors are the predominant species above the whiskey.

BTW: after watching barrels debunged for tasting and then being rebunged for storage, I've never seen anyone in the industry even blink with concern over oxidation in a barrel.

If they're not worried, I'm not worried.

[Leopold]

Some distilleries are indeed concerned with positive pressure on barrels, and therefore drill small holes on the side of the barrels, rather than remove the bung.

As far as small barrels are concerned (5-15 gallons), oxygen uptake is actually much higher than it is for the standard 53's. But the spirit needs time to oxidize. In other words, because the liquid to permeable membrane (the staves) ratio is high, more gases move into the barrel. But the compounds in the barrel need time to react with this increased level of oxygen. You can't mimic this. You need time.

While these reactions are waiting to happen, extraction of compounds from the staves is running at a pretty alarming rate when compared with 53 gallon barrels. This is the big reason that small barrels are quite different from 53's: The rate of extraction and oxidation don't occur at the same rate that 53's do.

Same thing happens with Scotch barrels of various sizes. But the difference with Scotch and what some micros are doing is that the micros are allowing for 6 or 12 months of oxidation in new char, and Scotch is allowing over a decade of oxidation with second and third fill bourbon or sherry barrels.

The reason that these small barrels work so well, imho, is that the general public in the US associates heavy oak flavors and aromas with quality.

I've only used them once, and haven't really cared for the results.... but this is a personal preference.

[Leopold]

The oxidation process is a key element of aging, and as others have noted, small barrels don't allow for that.

Recall that both the distillate and the dilution water will contain quite a bit of oxygen in the white dog before it goes into barrels (transferring spirit will always add oxygen. This is why brewers purge tanks, pumps and hoses with co2 before transfer).

This initial oxygen is why eaux de vies can age (or rest, if you prefer) in glass. Changes and esterification will indeed occur. A little extra splashing around through pumping or filling a tank from the top rather than the bottom will increase these reactions....to a point.

I suspect that you'll see esterification in the aforementioned Diageo barrels, especially if the blokes who are running the experiment think about oxygen, and intentionally heavily oxygenate a couple of the test barrels before entry.

But you're right in that if you only let those small barrels sit for 6 months, the various congeners won't have adequate time to react with the increased oxygen levels you get in small barrels.

[nblair]

Great insights, Leopold! Thanks for posting.

I was messing around on Google Books (incredible what you can look up on there...) and saw this quote from Jimmy Russell. I thought it summed up the original question that was posed, without going too in depth.

By the sixth year, approximately 30 percent of the barrel's volume has been lost to evaporation. By the eighth year it is 33 percent and by the twelfth year, the Angel's Share is about 40 percent. But, as Mr. Russell reiterates, if a third hasn't evaporated, it's not ready yet. "If a third isn't gone, the Angel hasn't gotten his share, so it's not any good yet."

[sailor22]

It's not just lack of complexity. Whiskey in new small barrels can quickly pick up a bitter unpleasant taste. Sort of like concentrated green oak tannins.

[Gillman]

I agree with you fully Steve. I don't know if that is because the whiskey doesn't stay in them long enough, i.e., ongoing oxidation and cycles might modify that taste, or something else explains it. (Are those small barrels made from staves dried and charred in the same way as for conventional whiskey barrels?).

One thing too that has always puzzled me is, why don't small amounts of spirit long resident in oak - very old spirit usually - oxidise as partly filled bottles will over time? I have had countless old rums, bourbons, malts, etc. where the barrel for years might be 1/3rd or less full. A bottle half-full kept for 20 years usually will oxidise, there is a characteristic metallic, "dirty" smell and taste I've often had at Gazebos in old bottles proferred. Sometimes it happens even when the bottle is full. But never in the barrel, ever that I can recall!

Gary

[squire]

Hello AK, welcome aboard. A thought provoking question that got some good answers and that's what this Board has been about for years.

Lacking a technical bent of mind I wouldn't attempt any answer deeper than to say it's done that way because that way works.