Special thanks go to WineWootaholic (WWA) for several topic suggestions, because he wasn't afraid to ask!
Barrels have been around for a couple of thousand years. While they are now used almost exclusively for wine and spirits, they are extremely versatile containers that had a multitude of applications for most of their history. If you know anyone with the surname of Cooper, they are the descendant of a barrel maker. Barrels have been used to store and move practically everything from soup to nuts: nails, grain and flour, olives, gunpowder, oil, all sorts of beverages, et cetera. They provided sturdy watertight, insect and rodent proof, portable containers. The bent staves of a watertight barrel also allow for easy movement by hand. A single person can readily move hundreds of pounds of goods rapidly across any somewhat flat surface, up a ramp, and even up a broad flight of steps. Imagine trying to move a six hundred pound crate by hand. Barrels were one of the easiest ways to move goods prior to the development of modern-day devices such as forklifts and elevators...
Oak has long been the wood of choice for barrels, and the reasons are pretty easy to guess at: it is plentiful, strong and supple, and generally watertight. The use of oak as a wine “ingredient” is a more modern phenomenon, and somewhat incidental to oak's practical use as storage and shipping containers. Part of the expected aromas and flavors of some regional wine types are acquired tastes based on the properties of the barrels traditionally used in those regions. The contrast of Burgundy and Bordeaux, the two regions with the longest history of small barrel usage, is interesting. The 228 liter (60.23 gallon) pièce of Burgundy is shorter and fatter than the 225 liter (59.44 gallon) Bordeaux barrique, which means that its staves have more curve to them. The staves need to be heated in order to bend them into shape without cracking, and fire is the traditional heat source. Because the pièce must be heated more, its staves are charred more during the bending process, and the resulting “heavy toast” aromas are an expected part of the Chardonnay and Pinot Noir profile, whereas they would be atypical in a Merlot, Cabernet sauvignon or Sauvignon blanc.
Until the California wine renaissance that began in the late 1960's small barrels were rarely used outside of Bordeaux and Burgundy. Beaulieu used small American oak barrels for their Private Reserve Cabernet sauvignon, but there weren't a lot of others. Because of James Zellerbach's deep pockets and strong desire to emulate the wines of Burgundy, Hanzell was the first winery to use French oak in California, just over 50 years ago. In the mid 1960's Dick Graff, founder of Chalone, was the first to set up a business importing French wine barrels. The use of oak as a winemaking tool, not just a storage vessel, blossomed after that. American consumer preference for strong oak aromas and flavors has even led to increased use of new oak in famous European wine regions such as Burgundy in recent decades.
There is a common generalization that American oak is inferior to French oak. Of course nothing to do with winemaking is ever that simple. French coopering is a long established tradition, and techniques and products have not changed substantially in recent decades. On the other hand, American oak wine barrels bear virtually no resemblance to the American oak wine barrels of thirty years ago, and coopers of American oak are still actively fine tuning their processes. It must have been ten years ago that Kent Rasmussen proclaimed that there “won't be a single French barrel sold in this country ten years from now.” Of course, ten minutes later he said he would never put his Pinot Noir in American oak :-).
Thirty years ago the only American oak barrels available were those mass produced for the distilled spirits industry. They were kiln dried, steam bent, cheap and ugly. Most wineries filled them with a strong solution of soda ash for a couple of days to get rid of flavor and tannin, followed by citric acid and hot water. Often they were filled with a cheap wine for a while to further mellow them for use with the better wine. Nadalie in 1980 and Demptos in 1982 were the first two French cooperages to set up shop in the United States. They assembled barrels from imported French staves and also started to cooper American oak using traditional French techniques such as air drying the staves and hand forming the barrels using fire. This first generation of American oak wine barrels was a huge improvement over whiskey barrels, but still dramatically different from French oak barrels. Since then experimentation and winemaker feedback have resulted in considerable refinement of American oak wine barrels. Wood selection (by grain, species and region - from Oregon to Pennsylvania, Minnesota to Arkansas), stave aging and toasting technique have all been adjusted to improve the final product. In blind tastings of barrel trials it is no longer easy, and in some cases virtually impossible, to tell which barrels are French oak and which are American oak.
Oak for wine barrels is also sourced from throughout eastern Europe, and I've even seen Chinese wine barrels at trade shows, though the level of “craftsmanship” is rather appalling. As a natural product, oak varies not only by source, but tree by tree and even within a single tree. There is more variability within a given region such as Alliers than there is between regions. The best cooperages are very diligent in wood selection and consistent in drying and coopering technique. I'd rather have consistent barrels with a more general source (center of France), than variable barrels with a sexy appellation like Bertranges or Jupilles.
One of the most common questions I get during cellar tours is, “How often do you need to replace the barrels?” It depends on how much oak aroma and flavor you want in each wine. Some wineries use 100% new oak and sell their barrels after one use. Extraction follows a geometric function, with roughly half the “flavor” being released into the wine during the first year. Some barrels are extracted faster, some slower, but they typically are fairly neutral after three to five years. Because the rate of extraction is asymptotic, barrels never become completely neutral. Extraction rates don't change when you refill barrels with a new wine – there is no equilibrium of extractable components between wood and wine.
WWA asked, “Why ferment in barrels rather than just aging fermented wine?” The primary reason is flavor integration; The most readily extractable oak components interact with grape components and yeast, giving more complexity, versus having wine flavors plus oak flavors. Also there is a “self-fining“ effect: some of the harsher oak and grape compounds are precipitated during the process, improving the texture and harmony of the wine. The cleaner a wine is when it goes into barrel, the more obvious the oak in the finished product.
WWA also asked about barrel cleaning and maintenance. Barrels must be either completely full of wine or empty, clean, dry and treated with a bacterial inhibitor such as SO2 to prevent growth of spoilage organisms. Because wine evaporates through the staves, barrels must be “topped up” regularly unless you want to make vinegar or sherry. Barrels are cleaned with a water spray at each racking, and after emptying for bottling they are cleaned more thoroughly (often with ozonated water these days), dried and given a little blast of SO2 gas, which is typically replenished every month or so. If a barrel does show signs of vinegar bacteria growth there are a few ways to try to save it. Soaking with ozonated water or Peroxycarb (sodium percarbonate, the active bleaching ingredient in non-chlorine laundry soaps) are two of the more common approaches. Chlorine is a big no-no due to its interaction with wood and the strong risk of TCA (“cork taint”) formation. If all else fails there's the gasoline treatment: an ounce of gas and a match (THIS IS IN JEST, DO NOT TRY THIS AT HOME OR ANYWHERE ELSE).
For more comments about oak, and specifically about barrel alternatives, please see my Random Ramblings blog from April, 2008, A Paradigm Shift.
The next Random Rambling will address wine microbes, the good the bad and the ugly. If you have any topic suggestions or questions, please send me a PM.