I recently spotted an interesting thread over at the Count's joint, and just had to get involved. It concerned the recent experiments using "cling wrap" around aging barrels in an attempt to reduce the costs of the annual lost Angel's share. Diageo was one of the (very large) companies actually considering this. A saving of just 2 or 3% per year means millions to them.
Actually there have been a number of experiments with preventing alcohol from escaping from the barrel, and believe it or not they have worked, reducing the loss by around three-quarters.
Just one problem.
By keeping the alcohol (and water) in, you also keep air and oxygen out. What you may not know is that oxidation is an essential part of aging and development of rum flavors. Here's what I posted:
It seems that one of the wonders of oak aging is that alcohol and oxygen are exchanged in a manner that is not only traditional, but highly effective in creating the unique and wonderful aromas and tastes of rum.When I am faced with a new subject or interesting questions, I find it hard to let things lie and usually find myself researching once again. And so it went for this notion of - god help us - cling wrap. After much research the answers became clear (pun intended). Allow me to summarize:
1. Even the tightest grain oak barrels, well built and sealed are permeable (both ways) via (a) porosity and (b) the oak acting as an osmotic membrane.
2. Alcohol and water pass out, creating a vacumn. At first the barrel - particularly the ends - deflect and prevent open space above the product. This takes about three weeks.
3. The vacumn draws in outside air, but a very small vacumn always remains. Nonetheless oxygen necessary for successful oxidation and aging is indeed drawn in. About 20 cc/liter/year of air is drawn in, and is quite necessary for aging.
4. Older barrels become less permeable and thus are less effective at aging.
5. An experiment at Martha's Vineyard covered barrels with oxygen-permeable polyethylene covers that tended to reduce alcohol/water loss to about 1/4th of normal evaporation, but accordingly reduced air exchange, a problem.
This never seemed to bother the many family distillers of the Caribbean, but sure upsets the corporate idiots. I sure hope the future of rum is not taste engineers, additives and/or friggin cling wrap...
