Sunday, January 30, 2011

Oak species

Distribution of Q.alba
The most common oak species used in whisky maturation are Quercus alba (American white oak, Quebec oak, ridge white oak), Q.robur (pedunculate oak, English oak, common oak, truffle oak, stieleiche, roble albar) and to a lesser extent Q.petraea (Q.sessilis, Q.sessiflora, sessile oak, durmast oak, Welsh oak, steineiche, roble). All of them belong to white oaks (Q.Leucobalanus / Q.Lepidobalanus). Red oaks (Q.Erythrobalanus) are used mainly for furniture and construction. The most common red oak is Q.rubra (Q.borealis, northern red oak, eastern red oak) growing in North America. Red oaks are not native in Europe. White oak is preferred in cooperages due its higher concentration of tyloses, which make it more waterproof, and due to its flavor profile.

Quercus alba
Q.alba grows in the eastern part of North America. Other American oak species used in cooperages include Q.bicolor (swamp oak), Q.lyrata (overcup oak, swamp post oak), Q.macrocarpa (bur oak, blue oak, mossy overcup oak, prairie oak), Q.mühlenbergii (chinkapin oak, yellow oak, chestnut oak, rock oak), Q.montana (Q.prinus, chestnut oak, tanbark oak, basket oak), Q.stellata (post oak, cross oak, iron oak, rough white oak), Q.robur and Q.garryana (Oregon oak, garry oak, brewer's oak, shin oak, western oak). The distribution of these species is basically overlapping with that of Q.alba, except for Q.garryana, which grows on the west coast of USA. The species hydridize often with one another and exchange genes quite freely between species. Q.prinus is usually too porous to produce solid casks and Q.garryana is apparently used mainly to produce oak chips for wine industry. Oak used for bourbon maturation is mainly sourced from Kentucky and Missouri, where the dominant species are Q.alba, Q.bicolor and Q.macrocarpa. Their properties in cooperage and maturation are considered to be quite similar and they are practically impossible to differentiate just by the appearance of staves. Q.alba provides 45% of the white oak lumber in North America. Of scotch whisky casks up yo 97% are made of American white oak.
Quercus robur

Quercus petraea
European oaks used in cooperages are usually Q.petraea or Q.robur, but also Q.pyrenaica (Pyrenean oak, Spanish oak, rebollo oak) is used in Portugal and probably Q.dalechampii in eastern Europe. Q.robur tolerates frost and disperses its seeds better than Q.petraea, but it suffers usually more from drought and lack of light. Thus Q.robur is usually the first species to colonize a forest, followed by Q.petraea and various hybrids. Q.petraea dominates especially thick and dry forests, whereas fastgrowing Q.robur and Q.dalechampii prefer rich and damp soil.

Distribution of Q.robur (www.euforgen.org)
In Portugal and Spain Q.robur is dominant over Q.petraea, but both of them only grow in the northern parts of peninsula near the Atlantic coast. Q.ilex (holm oak, evergreen oak, holly oak) is by far the most common oak in Iberian peninsula, followed by Q.suber (cork oak, not used for casks) and Q.pyrenaica. Q.ilex grows with lots of branches and knots and is hard to cooper. Both Q.ilex and Q.pyrenaica have been used to build casks, but are not preferred by Spanish coopers or winemakers. "Spanish oaks" growing in southern USA are usually Q.falcata (southern red oak, swamp red oak) or Q.palustris (pin oak, swamp Spanish oak), which are red oaks and do not grow naturally in Spain.

Distribution of Q.petraea (www.euforgen.org)
French oak is famous for it's effect on wine. Q.petraea is usually dominant, especially in Allier, Nevers, Tronçais and Vosges. Notable exceptions are Limousin, Gascony and Cîteaux, where Q.robur dominates. Both species grow in virtually all of the big oak forests, but the proportions of pure species of the two and their hybrids vary considerably. In French forests 10-30% of oaks are hybrids (average 23%).

Q.petraea is dominant in Germany and Wales, but in eastern Europe, Baltia and Russia the oaks are mostly Q.robur, although some Q.petraea, Q.frainetto (Hungarian oak, Italian oak) and Q.dalechampii are also used for cooperage staves in southeast Europe.

Persian oak was used in Europe after the WW II. The species used in cooperages were probably mostly Q.brantii (Persian oak, a white oak), Q.macranthera (Persian oak, caucasian oak, not exactly white oak but Q.mesobalanus) and Q.mirbeckii (Q.canariensis, a white oak). Their quality was variable and not comparable with European or American oaks. South African wines are usually matured in either American or French (Q.petraea) oak, although some domestic Q.ilex and Q.robur is available.

Quercus crispula

Quercus mongolica
Japanese oak species used in cooperages are Q.crispula (Japanese oak, mizunara, miyamanara), Q.mongolica (Mongolian oak) and Q.dentata (kashiwa, emperor oak, daimio oak). Q.crispula and Q.dentata are the two dominant oak species in Japan and they hybridize with one another, although probably rarer than European Q.robur and Q.petraea. All the three species are white oaks, but contain less tyloses and more knots than European or American oaks. Therefore Japanese oak is harder to cooper watertight. Japanese oak (Q.crispula) has a unique sweet and spicy flavour profile probably due to different oak lactone isomer ratio. Q.crispula was earlier believed to be a variation of Q.mongolica, but is now recognized as an individual species. 

References:
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Gougeon RD et al. The chemodiversity of wines can reveal a metabologeography expression of cooperage oak wood. PNAS 2009; 106; 23; 9174-9179
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www.efloras.org
www.euforgen.org

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