Mushrooms are tasty on pizza, battered and deep fried, or stuffed with crabmeat. Maybe you like grilled portabellas with polenta, or shiitakes in a stir fry, but probably not mushrooms in your whiskey.
Fair enough, but mushrooms do help your whiskey taste good.
It only recently has become known that mushrooms of a microscopic sort play a vital role in the seasoning of American white oak (Quercus alba) for whiskey barrels. Scientists call it fungal colonization. It is an early part of the wood’s natural decomposition process.
As unpleasant as it sounds, the early stages of decomposition play a role in the production of many wonderful flavors, from aged meat to Sauternes wine. The natural decomposition of oak is a complicated system that involves various biological and chemical processes that break the wood down into its component chemicals. These then become fodder for other organisms and processes.
For our purposes, these processes reduce too-high levels of some substances, such as tannin, while making others more available for absorption by the spirit, such as sugar.
You don’t want logs that are full of rot, of course, but a little decomposition can be tasty.
Cooperage, the craft of making barrels, is even more ancient than the craft of making whiskey. Both are a charming blend of the very traditional and very modern. The earliest coopers used pine because they didn’t have tools that were hard enough to work hardwood, but those barrels had to be sealed inside with pitch to prevent pine sap from damaging the contents.
When iron tools became available, coopers discovered that white oak doesn’t leak. The flavor benefits were a happy accident.
Historically, barrels were multi-purpose containers. Today, cardboard, plastic, and metals such as aluminum and steel do most of what barrels used to do. The primary buyers of new oak barrels these days are wine- and whiskey-makers. Without the beverage alcohol industry, barrel-making would be a lost art.
Brown-Forman Corporation is the only whiskey-maker that also makes barrels. They have a large cooperage in Louisville and have just opened another one in Alabama, strategically located close to some large stands of white oak and also that little distillery they own in Lynchburg, Tennessee. That is where most of the barrels from both Brown-Forman cooperages wind up.
Despite the fact that it makes barrels only for its own use, Brown-Forman is one of the two largest barrel-makers in the country. The other one, which makes barrels for everyone else, is Independent Stave Company (ISC). They are based in Lebanon, Missouri, but also have a large cooperage in Lebanon, Kentucky. (It gives tours.)
In addition to whiskey barrels, ISC is a major wine barrel producer.
There are several other cooperages, all much smaller than Brown-Forman and ISC. Since Brown-Forman and ISC strictly make 53 gallon barrels, it is the small cooperages that supply small distilleries with small barrels.
Although cooperage is more automated today than it was 150 years ago, it still requires considerable human skill. Machines can plane staves and cut heads, but they can’t arrange the staves in just the right way so the barrel won’t leak. Only a highly-skilled human can do that.
The selection and arrangement of staves is called ‘raising’ the barrel. Barrel raisers are paid per-barrel. The best are very well compensated and have great job security.
In addition to making new barrels, the craft of cooperage includes reassembling and refurbishing used barrels, as well as barrel repair. Most large distillers have coopers on staff to perform repairs. Many of the smaller U.S. cooperages and virtually all Scottish and Irish cooperages are primarily involved with used barrel reassembly, refurbishing, and repair.
Back to those mushrooms, fungi if you prefer. Carried by air, the spores land and send out roots (hyphae) that penetrate into the wood structure, where they release hydrogen peroxide. This natural bleaching and oxidizing agent helps break down the wood chemically, softening tannins and caramelizing hemicellulose among other salutary effects.
First in the pool (a fresh-cut oak is about 60 percent water by weight) is Aureobasidium pullulans, one of the species of common mildew, the same black stuff you clean off your shower tiles. As the wood dries it becomes inhospitable to pullulans which pulls out (okay, dies) and is replaced by another type that thrives in the slightly drier environment.
One after another a succession of different fungal species (eumycota) and sub-species each have a go at it, including the one from which penicillin is made.
In studying these mushrooms, modern science proved the superiority of a traditional cooperage practice – natural air drying – that had been widely abandoned in the United States after World War II in favor of kilns.
As they discover how much is really going on, coopers and distillers have begun to talk of wood seasoning, instead of drying. This is part of the new science being applied to this ancient art.