The oak wine barrel is one of the most familiar symbols associated with wine. We have romanticized the barrel and the act of ageing wine inside it to such a degree that, after the barrels have been used for their intended purpose, we often turn them into tables, benches, flowerpots and even candle holders.
According to historians, barrels were developed during the Iron Age and later, during Roman times, they were widely used for holding water, beer, milk, olive oil and wine. Wooden barrels had largely replaced their clay counterparts by as early as the second century BC. The most significant advantages of wooden barrels were firstly their strength, being made of wood and set round with metal hoops that bound the joints of the barrels into a double arch; and secondly, the barrels themselves were like wheels and could easily be rolled from one resting place to another.
But while, for centuries, oak was used for storage and transportation of wine, it’s only in the last 100 years or so that it gained recognition about its contribution to the taste of wine stored inside. Apparently, this realisation was an accidental historical coincidence. The storage of wine in oak wood resulted in the creation of wine with richer, more complex flavour and texture.
Wood for wine storage requires certain desirable properties, for example it should be straight grained, strong, resilient, and easy to work. It should be free of defects that may cause leaks, and should not contribute undesirable flavours. When these qualities are considered, very few woods seem suitable. Several types of wood have been tried for making wine barrels e.g. cherry, chestnut, acacia, redwood and many other species of tree have been turned into barrels for winemaking, but not one has become as vital as the mighty oak. Oak wood is strong and resilient. Because of its supple feature, the wood is bendable and can therefore be shaped into a barrel. Furthermore, oak is plentiful in the forests of continental Europe and offers a waterproof storage medium. Until a few decades ago, oak origin was of little consideration. Today, a great deal of importance is placed on its origin, not only the country but specific regions and often quite small areas within a country.
White oak of the Quercus type is almost exclusively the only category of wood used in barrel making because of its affinity for wine. Red oak is never used for winemaking because it is too porous. There is a plethora of Quercus species from many regions of the world to choose from, each having different characteristics and therefore imparting different aromas, flavours, and mouth feel, all of which are influenced by such factors as regional forest climate, age of trees, and tightness of wood grain.
While there are many different types of white oak, three are most used for wine processing. These are Quercus Petraea (also known as Sissile oak), Quercus Robur and Quercus Alba. In Europe, oak trees throughout the area ranging from northern Portugal, France, the Baltic States, Hungary and Romania, belong to the Quercus Petraea and Quercus Robur families. Both are considered suitable for wine making. Yet a good deal of diversity in flavour and structure is evident depending on the precise microclimate, soil structure and density in which the trees grow. This difference is notable particularly with oak from France, possibly because it is only in this country that the regions of origin have been carefully defined. In France, oak wood comes primarily from forests located in four main regions namely Limousin, Centre, Bourgogne (Burgundy) and Vosges.
Quercus Alba is a white oak of the renowned hardwoods of eastern and central North America. It is grown mainly in the eastern states as well as California. The forests in Minnesota and Wisconsin are considered particularly good sources of oak for the wine industry. Quercus Alba is predominantly used for American and Canadian barrels, which tend to impart more “oakiness”.
Eastern European (Slovenian & Hungarian) Petraea (or Sessile) oak is structurally similar to what is found in France, yet it has slightly different qualities including less tannin. These trees grow more slowly and are smaller, creating fine grain and extremely subtle extraction. In recent years, oak from Hungary, Austria and even Russia is increasingly proving to be good. Some local oaks are less suitable though and it’s not always clear whether this is due to the oak species, the forestry management, the climate or the process of ageing and coopering the wood.
The effect of a specific type of oak on different wines has been the subject of great discussion and experimentation among wine makers throughout the world. In order to appreciate its impact on winemaking and wine style, one has to understand the chemistry of oak wood. During ageing in oak barrels, the composition of wines change because of the addition of phenolic compounds and other molecules extracted from the wood. The main constituents of oak are shown below:
Amount as % dry weight
Cellulose is the major component of the cell wall. It contributes to the strength of the wood and undergoes little change during the processing period. Hemicellulose acts as a binding agent and holds cellulose and lignin together. When in contact with wine, hemicellulose can be hydrolysed into sugar and the acetyl group, which can subsequently be converted to acetic acid during wine maturation. Heat treatment of wood (toasting) causes decomposition of hemicellulose, yielding several compounds.
Lignins have been described as branched chain phenylpropanoid polymers. During seasoning and toasting, Iignins undergo substantial chemical changes. Many compounds resulting from the thermal degradation of lignin play a key role in influencing wine flavour. Some of the important lignin breakdown products and their aromatic properties are: Vanillin (vanilla), Guaicol (smoky) and Eugenol (spicy, clove-like),
Tannins protect the wood against fungal attack and help in the preservation of wood. Oak tannins are chemically different from the condensed tannins found in grapes and wine. They are polymers of gallic acid, ellagic acid, and glucose. Some of the other compounds found in oak heartwood include resins, sterols, fats, and lactones. Oak lactone, increase during toasting of the wood.
The organoleptic texture of oak barrel is also greatly influenced by production methods, namely, how the wood is milled (split vs. sawed), how it is dried (air vs. kiln) and for how long, and the extent of toasting (light vs. medium vs. heavy). This means that oak compounds transferred to wine can have dramatically different characteristics and chemical behaviours that will impact wine chemistry and quality and how it evolves and changes over the period the wine is aged in barrels.
Both American oak and French oak contribute aromas, flavours and tannin to a wine. French oak (particularly Quercus Petraea) is much tighter grained and less dense than the American Quercus Alba. As such, French oak imparts more subtle flavours and firmer, but silkier tannins. American oak being denser, can be sawn instead of hand-split. This involves less labour and expense. Hence American oak barrels are considerably cheaper than their French counterparts.
Furthermore, barrels made from American oak add sweeter texture and contain more vanillin compounds and tend to impart more obvious, stronger and sweeter aromas and flavours. Common descriptors for American oak apart from vanilla are coconut, sweet spices and dill. Some other very important factors of oak barrels which exhibit influence on the wine include the age, level of toast and size of barrel.
The newer the oak the more oaky aromas and flavours imparted. By the fourth or fifth pass, negligible flavour is left to impart. It has been shown that the impact or effects of the oak barrel diminish after four uses of the barrel and some elements like vanilla seem to be lost after just 12 months of wine contact.
The newer the oak, the more oaky aromas and flavours imparted. By the fourth or fifth pass, it has been shown that the impact or effects of the oak barrel diminish and some elements like vanilla seem to be lost after just 12 months of wine contact, with negligible flavour left to impart.
The benefits of fermenting or ageing wine in toasted oak barrels are indisputable and unmatched by any other type of wood. The higher the level of toast (high, medium or light toast) the more oaky the aromas and flavours, and the smaller the oak barrel, the greater the impact of oak aromas and flavours. Not only do oak compounds impart aromas and flavours as well as body and structure, they also help improve wine colour and stability. Speaking strictly from a flavour stand-point, it also allows a slow, controlled amount of oxygen into the wine that also increases the wine’s rate of maturity.
The down-side of the wine barrel is cost. They are a substantial investment for the winemaker. Assuming a barrel gets used for three years, this is translated to around 1 euro per bottle just for the oak, never mind the cost of a special barrel cellar and all the extra handling. Because new barrels are expensive, their use is usually reserved for premium wines. But winemakers are only human: they want the beneficial effects of oak for their cheaper wines as well, without the high cost.
As a result, barrel substitutes have become increasingly popular. These can range from small oak chips in teabag-like nets to barrel staves bolted into the inside of the tank. Results can be variable, and are generally not as good as those achieved by barrels. If you see the words “oaked” on the label of an inexpensive wine without mention of barrels, the chances are one of these alternative techniques has been used.
All of the above-mentioned variables contribute to the results with fuller and richer complexity and impressions that can only be achieved with fermenting and ageing wine in oak barrels. For many great wines, oak is simply an essential ingredient. Alternatives don’t provide the same level of complexity. Proper balance and increased consumer education on the benefits of oak alternatives may be the best solution for winemakers in this current state of flux in the consumer wine market.
When all is said and done, every wine, whether aged in oak or stainless steel, has its own elite group of followers. And for the consumer, it is a win-win situation because they have the option of enjoying wines created by both processes, depending on their mood. Wine created through both methods are easy to enjoy and appreciate.