Coopering



Cooper in the Guinness brewery, late 19th century

Wooden barrels have been used to store wine since ca 500BC. Whisky has probably been stored in barrels from the invention of distilled malt spirits, altough the significance of maturation has been commonly appreciated from the  latter part of 19th century. In 1915 it was made compulsory for Scotch whisky to be warehoused in bond for a minimum of two years and the age limitation was extented to three years one year later. In 1988 the Scotch Whisky Act declared that the maturation had to take place in wooden casks of a capacity not exceeding 700 litres. The wooden casks were specified to be made of oak in Scotch Whisky Order 1990.

Until the 16th century the oak used in cooperages of United Kingdom was mostly English. After that shipbuilding and construction increased the demand for quality oak and imports of oak staves increased. There was even a legistlation from 1543 prohibiting export of casks larger than barrels and making exporters import a corresponding amount of timber for casks. The British imported oak came mostly from the Hansa region (Denmark, Baltic), Russia and America (Virginia, New Orleans). Used wine barrels especially from Spain and Portugal were also common. Spanish and Portuguese coopers preferred American oak, whereas British coopers preferred Memel oak over American, European and English oak.

Memel (now Klaipèda) was an important port in Baltia (Lithuania) providing timber from the Baltic region and Russia. Memel was the golden standard of quality oak for the British until 1930s, but during and after the second world war it became unobtainable in UK due to rise of Soviet Union in Baltia. In addition the Spanish civil war (1936-1939) decreased the amount of imported oak casks from Spain. In the 1930s and 1940s Polish, American and English oak was used. In the 1950s Memel oak was already available, but because of the loss of woods in the wars and difficulties in trade the price was high.

Speyside cooperage

From the war years until 1956 as much as 90% of oak used in UK breweries was Persian oak, probably of species Q.brantii (Persian oak, a white oak), Q.macranthera (Persian oak, caucasian oak, not exactly white oak but similar Q.mesobalanus) or Q.mirbeckii (Q.canariensis, a white oak). The quality of Persian oaks varied greatly, probably due to different species harvested and the long transportations in too hot climates. The amount of Persian oak casks used in whisky industry is not recorded. Wine and spirit shipping casks were used widely and apparently preferred for maturation of whisky, especially sherry casks from Spain and port wine casks from Portugal.

Oak maturation of quality American whiskey became a norm during the late 1800s, whisky from Kentucky being sold with age statements from 1840's. Most American bourbon is supposedly matured in charred new Q.alba, but also other American white oaks and their hybrids are used either on purpose or by mistake, since the species can be quite hard to distinguish even with DNA-testing and practically impossible to differentiate only by inspecting the staves.  Since 1938 bourbon has had to be matured in new oak wood, resulting in great number of reasonably priced used casks available from the USA to Scottish whisky industry. In the 1960's the American cooperages produced up to 2.3 million casks a year, about twice as much as today. Because of the surplus bourbon casks the prices dropped and resulted in diminishing use of sherry casks during the last decades, especially as the amount of sherry shipped in casks dimished. Today over 90% of Scotch whisky casks are ex-bourbon. The barrels are usually dismantled into shooks during transportation and assembled again in Scotland. Usual practice is to convert the barrel sized (150-220l) bourbon casks into bigger hogsheads (about 250l) by adding a couple of extra staves of either new or used wood. Some bourbon producers are now using hogshead-sized casks, too. The casks in Scotch whisky industry are filled usually three times before discarded or rejuvenated by seasoning and/or toasting. Other types of American whiskey (not bourbon) have been allowed to mature in refill oak casks since 1970. Whether the Scotch whisky industry has utilized these American refill whiskey casks is not known. Some American red oak has been used in maturing spirits and beer, most notably Guinness beer from late 1800s to early 1900s, but generally red oak casks are not used anymore.

Manuel González Gordon

Sherry producers use mostly new American oak, usually toasted and not charred, but at least some Spanish Q.robur from Galicia is used. In the 1960's and the 1970's Costa Rican red oak varieties Q.costaricensis, Q.eugeniifolia and white oak Q.copeyensis were used (and esteemed) in the Sherry region, but I have no information of the scale of this nor whether they are still used. The sherry producers have been using at least some American oak from the 1600s and nowadays use it almost exclusively. A note from 1807 by Spanish botanist Esteban Boutelou (1776-1813): "The great wine shippers cooper themselves the casks they require for their trade...They use oak almost exclusively; and they esteem more than any that which comes from the United States of America, next the Northern oak, then the Italian and lastly the Spanish... wines ferment better in butts and wooden vats than in earthenware, which belief is shared by the Sanlucar growers.". Hardman (1878) reports that American oak is used exclusively for sherry and marsala production. The great sherry authority Manuel González Gordon writes in 1948 (and in later editions 1972 and 1990) that "In Jerez no other wood has been used for many years, as American oak has given the best results for the fermentation, maturing, ageing and shipping of Sherry." and "In recent years some Spanish oak has been used [for shipping sherry], due principally to the difficulties of importing American timber". Of the big sherry importers Gonzalez-Byazz, Sandeman, Williams-Humbert and Lustau declare they use mostly American oak and I have not yet found a firm using only European oak. It is safe to assume that the whole Sherry region has used mostly American oak for at least the last two centuries and the majority of the Spanish oak casks used in Scotch whisky industry are in fact Spanish-coopered American oak casks. Some European oak (Q.robur, Q.pyrenaica) sherry casks have sold to Scotch whisky producers either by chance or by special order from for example Edrington Group (owner of Macallan, Glenrothes, Highland Park,Tamdhu, Glenturret), Glengoyne and Gordon&MacPhail. Sherry shipments by the cask have practically ended since Spain became member of EEC in 1986 and bulk shipments of wine fortified over 15.5% ABV became prohibited inside EEC. Usually only some fino sherries are below 15.5% ABV and the olorosos preferred in whisky maturation are often over 18% ABV. In addition, if the lower strenght sherry wines with the status of Denominación de Origen (DO) are to be shipped in bulk, the containers must be approved and sealed by the Consejo Regulador de Jerez and the wine must be accompanied with detailed certificates of analysis. Only the biggest sherry houses (Bodegas de Crianza y Expedicion) are allowed to ship sherry in bulk (64 different houses at the moment). Understandably practically all sherry casks are shipped empty or dismantled to shooks.

Apparently there is no official definition for "sherry cask" in Scotch whisky industry, so some of the so called sherry casks might be ex-bourbon casks treated with sherry or similar products such as paxarete wine (a heavy sweet wine from the Sherry region). The size of sherry cask is by law under 1000 litres, usually a butt contains 30 arrobas (about 500 litres), although a variety of different size casks has been used (octaves, hogsheads, gordas, bocoys etc).

In Portugal "imported oak is preferred". American, Polish, French and even Brazilian (no idea of the species) oak has been used, although considerable amounts of Q.pyrenaica and even Castanea sativa (chestnut) has been used as well, at least in red wine maturation and port wine shipping casks. Since 1986 the same EEC shipping rules apply to fortified port as to sherry (see above). The size of port cask (pipes) is usually slightly bigger than the cask size for sherry or other wine casks.

French oak has been used extensively in wine cooperages and lot of research has been made concerning diffrent oak species and local variance of wood as well as its influence on wine maturation. Traditionally local oak has been used to mature local wines, but recently the knowledge on oak qualities has lead to various experiments with different oaks and combinations of oak species. There are lots of variation between the species and the forests, but generally Q.petraea is considered to be of better quality for wines, especially for the whites. Wine casks are usually barrique sized 225l.

Q.robur (Limousin, Gascony, Cîteaux, Galicia) is used to mature spirits, most notably cognac and armagnac. Armagnac producers do use different species of oaks, but the most appreciated is "black oak" of Monlezun forest in Gascony. Black oak is probably a variation of Q.robur. Cognac producers prefer Q.robur from Limousin; new casks are used to mature inferior cognacs or for just a short period (months) in the beginning of maturation before reracking the spirit into old (usually bigger) casks for longer maturation. Cognac casks are usually sized 270-450l, the most popular size being 350l.

Q.crispula, Q.dentata, Q.serrata and probably Q.mongolica are used in Japan. The Japanese mizunara casks are commonly 500l casks and often seasoned with sherry.

General rule of the thumb seems to be that casks made of European Q.robur or American Q.alba are preferred in spirit maturation over Q.petraea in various spirit producing areas and for longer maturation periods refill casks are preferred, except for bourbon.

http://whiskyscience.blogspot.fi/2011/02/coopering-part2.html

References:

Calabrese S. Cognac, liquid history. Cassell&Co 2001
Crowgey HG. Kentucky bourbon, the early years of whiskeymaking. Univ Press Kentucky 2008.

Deguilloux MF, Pemonge MH, Petit RJ. DNA-based control of oak wood geographic origin in the context of the cooperage industry. Ann For Sci 2004; 61; 97-104

Doussot F, De Jeso B, Quideau S, Pardon P. Extractives content in cooperage oak wood during natural seasoning and toasting; influence of tree species, geographic location and single-tree effects. J Agric Food Chem 2002; 50; 5955-5961

González Gordon M, Sherry. Cassell Ltd 1972

Gougeon RD et al. Expressing Forest Origins in the Chemical Composition of Cooperage Oak Woods and Corresponding Wines by Using FTICR-MS. Chem. Eur. J. 2009, 15, 600 – 611

Gougeon RD et al. The chemodiversity of wines can reveal a metabologeography expression of cooperage oak wood. PNAS 2009; 106; 23; 9174-9179
Halley, N. Sandeman: two hundred years of port and sherry. Granta Editions 1990.
Hardman, W. The wine-growers and wine-coopers manual. Wm Tegg London 1878

http://eur-lex.europa.eu 

Jackson, RS. Wine Science. Academic Press 2000.

Kilby, K. The cooper and his trade. John Baker Publishers Ltd 1971.

Lepais O et al. Species relative abundance and direction of introgression in oaks. Molecular Ecology 2009; 18; 2228-2242

Monica Lee KY, Paterson A, Piggott JR. Origins of flavour in whiskies and a revised flavour wheel. Review. J instit brew 2001; 107; 5; 287-313

Mosedale, JR. Effects of oak wood on the maturation of alcoholic beverages with particular reference to whisky. Forestry 1995; 68; 3; 203-230

Page CE. Armagnac, the spirit of Gascony. Bloomsbury Publ 1989

Prida A, Ducousso A, Petit RJ, Nepveu G, Puech JL. Variation in wood volatile compounds in a mixed oak stand: strong species and spatial differentiation in whisky-lactone content. Ann For Sci 2007; 64; 313-320

Prida A, Puech JL. Influence of geographical origin and botanical species on the content of extractives in american, french and east european oak woods. J Agric Chem 2006; 54; 8115-8126

Read J. Sherry and the sherry bodegas. Sotheby's 1988

Reid KJG, Swan JS. Assessment of Scotch whisky quality by pyrolysis - massspectrometry and the subsequent correlation of quality with the oak wood cask. J Anal Appl Pyrol, 1993; 25; 49-62

Singleton VL. Oxygen with phenols and related reactions in musts, wines and model systems. Am J Enol Vitic 1974; 38; 69-77

Swan JS. What's best for barrels: air or kiln-drying? Wines & Vines. July 1993

Twede D. The cask age: the technology and history of wooden barrels. Packag techol Sci 2005; 18; 253-264
www.legislation.gov.uk/ukpga/1988/22