cork has been the dominant choice of closure for beverage containers for centuries. Its flexibility, strength, and durability have made it an ideal closure, particularly in irregular glass bottles in the years before machines provided greater bottle uniformity. It is made from the bark of cork oak, legally protected trees in Portugal since the thirteenth century, and which today account for more than 20 percent of that country’s forested landscape. Although natural cork only accounts for about 5 percent of the spirits closures market, it is used in a great many of the most prestigious spirits: single-malt scotch whiskies, small-batch bourbons, old brandies, sipping rums, añejo tequilas, and the like. Spirits corks generally take the form of a short cork glued to a wooden, plastic, or metal flange that enables the user to pull it out without a corkscrew.
Cork oak (Quercus suber) is a renewable resource; its bark can be stripped away for a century or two without damaging the tree. The industry norm sees a first stripping at twenty-five years old, a second stripping at thirty-four years old (both of which are used for other industrial purposes), and then subsequent strippings every nine years for the creation of bottle corks. Its cambium structure contains pentagonal and hexagonal cells (Richard Hooke’s eighteenth-century study of cork led to his coining of the term “cell” for life’s building blocks), almost a billion in each cork, which gives cork its useful properties of lightness, flexibility, resistance, and modest impermeability.
From the early 1980s onward, wine buyers began identifying cork closures that exhibited the wet cardboard-like, off aromas of TCA (or 2,4,6-trichloroanisole), and the market reacted by adopting synthetic corks and screwcap closures. Contrary to popular belief, the high alcohol content of spirits does not prevent TCA from forming or spirits from getting corked. The incidence of this is lower than that with wine, since fewer spirits producers use cork closures, preferring metal or plastic screwcaps, but when it does occur, it is likely to affect higher quality, or at least more expensive, spirits, as those are the ones most likely to use corks.
The large cork producers have responded to the TCA issue by altering their processes to decrease its incidence; estimates of 5–10 percent TCA occurrence (in wine) now seem much closer to 1–2 percent, and at least one producer touts a brand that is guaranteed to be 100 percent free of detectable TCA. Other changes have taken hold in the industry. Chlorine bleaching of corks to create standard coloration, for instance, has been discontinued (chlorine is a TCA precursor compound). Sterile conditions in the cork factories and even in the harvest fields (e.g., cutting no lower than 1.3 meters from the ground) have improved matters as well.
Despite these challenges, cork remains the most common wine bottle closure and is also increasingly used for spirits as the industry trend toward premiumization continues. Tasters have noticed an increase in corked spirits. As the wine industry has learned vigilance, spirits producers will have to do the same.
Amorim Cork. Institutional Presentation, 2014.
Jackson, Belinda. “The New Zealand Screwcap Wine Seal Initiative-Ten Years On.” Wine Business Monthly, February 2011. https://www.winebusiness.com/news/?go=getArticle&dataid=83546 (accessed March 1, 2021).
Johnson, Hugh. The World of Trees. London: Mitchell Beazley, 2016.
By: Doug Frost