American oak

American oak (Quercus Alba) differs from European oak in a number of respects. The most central point is the density of the wood. The American white oak has a greater ring density than the European sessile oak. This leads to a greater exchange of oxygen in the barrel, which increases the influence of the wood on the product. The majority of American white oak comes from the Midwest of the USA, Missouri and the Ozark Mountains. American oak is used to make bourbon barrels with a capacity of 190 liters, the so-called ASB (American Standard Barrel), as well as barrique barrels. The heat treatment of the barrel can be adjusted to produce a wide variety of aromas. Toasting is a thermal treatment of the wood that produces vanilla aromas, among other things. These vanilla aromas are much more pronounced in American oak than in its European sister. American white oak contains up to ten times more vanillin. By adapting the toasting, a wide variety of aromas such as dark chocolate, ripe fruit or sweet caramel can be produced.

Palatinate oak

As already mentioned, European oak has finer pores than American oak. The denser pores of the wood result in less oxidation, which makes the wood aromas more subtle and subtle. This is why this wood is considered to be particularly fine. More precisely, the Palatinate oak is the sessile oak (Quercus sessilius). Palatinate oaks grow on sandstone soils in the local low mountain range, the Palatinate Forest, for around 200 years. Only particularly fine-pored and straight-grown trees are suitable for barrel making. They are carefully selected and then carefully felled. The trunk is cut in a mirror cut and the staves are left to dry for several years in the open air, where they are deliberately exposed to all weather conditions in order to maintain the characteristic tannin structures in the wood. The staves are then processed into barrels of various sizes. Barrels of 225 liters (barrique), 500 liters (tonneaux), 600 liters (half-barrel), 1000 liters (barrel) or 1200 liters (unit barrel) are particularly common for wine production. However, barrels are also made from Palatinate oak that are smaller or larger than these examples. Traditionally, the staves are pulled together over an oak fire by a cooper to form a barrel. The subsequent toasting – usually in light, medium, medium plus or forte – also takes place over the oak fire. Depending on the toasting, there are also different aromas of red fruits, caramel or roasted coffee. In general, however, the tannins are more prominent in this wood and the vanillin content plays a much smaller role.

Slavonian oak:

Slavonian oak (Quercus peduncolator) is traditionally used for the construction of large barrels between 5 and 150 hl. In the Balkan region of Slavonia, the oaks literally grow in the swamp along rivers. Due to the high groundwater level in the growing areas, the water retains the tannins, which means that Slavonian oak has a more neutral taste. The wood tones can usually be found in the background during a tasting.

Mizunara oak:

The Mizunara oak (Quercus Juniperus), or water oak, comes from Japan and does not have as long a tradition in barrel making as the French or American oak. This is due to the fact that barrel making has only been practiced in Japan for less than 100 years, whereas in Europe the craft of cooperage has existed for over 2000 years. The twisted growth and high water content of this oak make it very difficult to process. Only a residual moisture content of 14% is allowed for the wood to be processed into barrels. These complicating factors mean that a barrel made from Mizunara oak is around 10 times more expensive than a barrel of the same size made from American oak. Compared to the other oak species, water oak has the lowest tannin concentration. As a result, “overwooding” occurs less frequently, which makes Quercus Juniperus all the more interesting for distillates. The Mizunara oak is very intense, especially at the beginning. Finer, more delicate aromas only develop after longer storage. It has a unique sweet but also spicy flavor profile, which is due to the high lactone and vanilla content. Aromas such as spices, kara (a type of oriental incense), sandalwood, coconut and vanilla come from barrels made from this special wood. Mizunara casks are particularly popular with whisky distillers, as the whisky can benefit enormously from the long storage in the cask.

Limousin oak:

The classic among oaks! The Limousin oak grows in large forests in central France around the city of Limoges. It is one of the most popular woods for making barrels. The rather large-pored and tannin-rich wood gives the product an expressive color and a pronounced tannin structure. In addition to wine barrels, Limousin oak is also used to make distillate barrels, for example for maturing cognac or eau de vie. French cooperages process the wood in a similar way to German cooperages. The sizes are also similar to those of barrels made from German oak. Barrique (225 l) or tonneaux (500 l) sizes are particularly common in France. French oak also has many sensory similarities to Palatinate oak. The different toastings also allow different aromas to be produced. For example, a distillate that has matured in a wooden barrel with medium toasting can have aromas of dark fruit, toasted bread and coffee. The aromas always depend on the thermal treatment of the wood, the type of distillate and the duration of storage.

Let us now turn to the special types of wood that are often used for barrels in viticulture, but also for spirits and beers. The following woods, which are mainly found in Central European forests, show – each on its own, but also in combination – an incomparable characteristic.

Mulberry tree (Morus):

Mulberry, a wood that has now become very rare. The last time I found it was at a timber sale in the Swabian Alb. The wood of the white mulberry is very hard, golden yellow in color and is used for the construction of distillate barrels, nowadays up to a stave length sufficient for a 225 l barrel. Larger staves can hardly be realized due to the growth height of up to 6 m. We generally toast the barrels lightly to medium in order to apply a manageable amount of wood sugar to the inner surface of the wood. The characteristics of mulberry barrels are sweet and spicy with a very high color release. The ageing time must be adjusted. Too long storage in the barrel spoils the spirit. With shorter maturation times, the mulberry refines the distillates with a pleasant sweetness.

Robinia (false acacia, Robinia):

This interesting tree with its extraordinarily hard wood can be found in the wild in our German low mountain ranges, especially in the Swabian Alb and the Palatinate Forest. The tree has a rich, sweet scent when in bloom. The wood is yellowish in color and very hard. It is ideal for barrel making. Depending on the selected toasting level, this wood offers fresh aromas, which are particularly appreciated in white wine, or even aromas of bacon and smoked ham, which some whisky lovers like on their maturing distillate made from smoked or peated malt. When it comes to fruit brandies, we recommend acacia above all for distinctive stone fruit varieties such as plums or very aromatic apple distillates, which should deliberately differ somewhat from mainstream calvados. As already mentioned, the selection of the right toast is particularly important. Toasting is a decisive factor when it comes to successful ageing with that certain “aha” experience.

Sweet chestnut (Castanea sativa):

Actually a very old barrel of wood, the Romans probably brought the chestnut from Asia Minor to our homeland. The Palatinate Forest in the Wasgau region is a special habitat for this tree species. The chestnut is a thermophilic tree, which may even have a future in the future forests of our homeland – but it also needs water! Chestnuts can be easily processed into barrels of all sizes and produce a woody, honey-scented aroma. Chestnut barrels give a good punch without the bitter tannins that characterize oak. In many deconstruction tastings in which chestnut casks are included in the blend, this type of wood proves to be a crowd favorite. It is particularly recommended for grain and whisky spirits, as well as for distillates with a particularly high starch content, such as a whisky with a predominantly maize component, bread distillates, etc. Chestnut can also be used in very distinctive distillates such as rowan or cherry, the latter in order to provide new approaches to maturation and flavor characterization. Here, the almond aromas go perfectly with the character of forest honey. Originally, chestnut wood was used to make large wine barrels, preferably barrels in which red wines were matured!

We are currently working on a revival of chestnut and, compared to other special woods and compared to oak, already in significant quantities, even industrial customers have been convinced of the advantages of this wood!

Real walnut tree (Junglas Regia):

Whenever the opportunity arises, we buy walnut trees at the timber submissions, as we do with all other types of wood. It is a valuable wood that is often not easy to process into staves. There has recently been great demand from our customers in the distillate sector in particular, including for testing purposes in the wine and beer segment.

The orders far exceed the supply of wild-grown trees that cannot be ordered.

It is worth a try to use the barrels made from walnut wood for different types of fruit. Just as is done in the country richest in walnut trees, Kyrgyzstan. Here, in the shade of large wild walnut trees, numerous original orchard fruit varieties grow, which are naturally distilled and matured in barrels made of walnut.

Bird cherry (Prunus Avium):

We often find this wild-growing tree in Germany’s low mountain ranges in considerable thickness and length. We can produce staves from these trunks for almost all barrel sizes up to 300 liters. Customers for these barrels, which we usually equip with a medium toast, can be found in the wine sector for Pinot Noir wines. This wood is also currently attracting a lot of attention among distillers, and new experiments are being made in the storage of gin.

Common ash (Fraxinus Excelsior):

A wood that is often found in floodplain landscapes and moist stand areas. The ash is of great silvicultural importance. It is often planted to secure slopes, provided fodder in past decades and was often used to make bows, tools and sledges.

In our segment, barrel making, ash was a very popular wood for softening distillates without giving them too much color or tannins and aromas. You can still find very old ash barrels in grain distilleries or fruit distilleries, for example, which are still in use, simply to give the product time to mature and marry with the air flowing in from outside. Ash has recently come back into fashion, and I’m particularly pleased about this – yes, in the small distillery segment for the delicately emerging “plant” of fruit brandies!

Last but not least, I would like to introduce you to our new barrel, based on sustainability considerations.

Kiri wood

A distillate barrel, we are also experimenting with wine and beer barrels made from Kiri wood – the so-called imperial tree. Outside of the forestry law, this tree grows on plantations – similar to sugar beet or other types of fruit and is harvested after approx. 11 years as a stately tree with a diameter of approx. 500 mm. According to analytical and sensory evaluations, Paulowina Imperialis is a highly aromatic wood with a high cellulose and lignin content, which can already be surmised from the physique of the oversized leaves.

Due to the high levels of lignin and hemicellulose, heat-reduced toastings, which can also be applied using electric heat and secondary heat sources (e.g. hot stones), prevent smoke aromas such as gujacol during toasting, but instead create high sugar molecules on the surface of the wooden barrel by breaking down the ingredients.

As a result, wooden barrels are produced which, in contrast to barrels made from traditional types of wood and known toastings, offer high aromas in the form of sweetness and vanilla when matured with distillates, wines or beers.

Conclusion:

The craft of cooperage is no longer tied to a single type of wood. Modern businesses can benefit from the sensory properties and characteristics of each individual species to create unique, competitive drinks.