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Oak and Oak Barrels - Why do winemakers get so excited?

Oak has had a very long association with wine. Initially it was simply as a watertight container that could be used for transportation of the liquid. It wasn't until the development of epoxy-lined cement and stainless-steel tanks that winemakers had alternatives. In this series we explore different how oak can enhance wine.

This page pulls together the different environmental issues that influence wine, starting with glass recycling in the UK.

Give me the BIG picture please

Oak has developed into its current marriage with wine because of two key reasons. It was perfect to shape into barrels. It is strong yet easy to work with and shape. It is also rich in tyloses, the compound that makes barrels watertight. Modern wine making does not need barrels but the majority of red wines rely on oak barrels for a vital component of their flavour, as do many whites. Without the influence of oak, wine would taste very different.

You can often taste and smell the influence of oak (vanilla is usually the easiest to find). The flavours enter the wine as it ages in oak barrels, with the newer oak barrels able to pass more flavour than barrels that have been used for 2-3 vintages. But as important as flavour is, the exposure of the wine to small amounts of air that seeps through the pores of the wood, the oxygen softens the wine and can change it profoundly.

The twin impact oak can have, make winemakers as fussy about the oak they use, as they are about the condition of the grapes. The differences between different types of oaks, French or American, can have a huge effect on the flavours the oak imparts. But oak barrels come from a living plant, ensuring that no two barrels are the same, and each barrel will influence the wine in a different way. This range of flavours can give the winemakers opportunities when they blend the different wines together. All this tasting and blending effort is time consuming and is generally worth while for £7 plus wines.

Some winemakers avoid using oak barrels completely but still achieve 'oak' flavours with stainless-steel or cement tanks and oak chips, oak staves or powder. These alternatives are giving the adventurous winemaker flexibility in the winemaking process and the possibility of new flavours and styles.

Geography - does it make a difference?

In the main, winemakers across the world use barrels made from either French Oak, American Oak or Eastern European Oak. Each geographic region has different species of oak with individual flavour compounds and structural characteristics.

Most French Oak comes from forests that were planted in the days of Napoleon for shipbuilding. Since the days of sailing ships have come and gone, those French forests have become ongoing forestry operations. Five primary forests used for wine barrel production are Allier, Limousin, Nevers, Trancais and Vosges. Interestingly, Vosges, in the north east of France, was the scene of many fierce battles in WW1. Up until the last 15 years very little oak was taken from Vosges as shrapnel embedded in the timber would damage saws and tools.

Each of these forests produces wood with distinctive characteristics involving tightness of the wood grain as well as the amount of oak flavours that are imparted to the wine. Tight grained wood tends to impart the Oak characteristics (vanilla, spice and butter flavors) much more slowly than wood with looser grain. Winemakers select wood for their wine barrels from different forests for the effect on the finished wine.

Experiments with American Oak (and that of many other countries) were not very successful since the amount of influence that the barrel had on the taste of the wine was too great. At first it was thought that the problem was with the wood itself. Now we know that most of the difficulties were caused by the way the wood was prepared and the way the barrel was constructed. As coopers began using traditional French barrelmaking techniques on 'foreign' oak, the results improved dramatically.

When examining French oak, we find the highest tannins of the oak types. Wine has easy access to an array of compounds in the more porous oak, providing multiple extractives. Structurally, French oak has less of the watertight giving properties of tyloses so the logs need to be hand split down the grain rather than sawed across the grain as with American oak. Logs sourced from the Office National des Forêts make for more expensive timber & therefore barrels.

Structural differences in American oak's hemicellulose and lignin result in more intense vanilla, wood sugars, and toastiness. Because stave timber is purchased from private landowners, log costs are lower. Its density, high tyloses, and straight grain means higher yields, machine cutting, and lower cost barrels.

Eastern European Slovenian & Hungarian) Oak is also available and has slightly different qualities to French Oak e.g. lower tannins. The trees grow more slowly and are smaller, creating a fine grain and extremely subtle extraction. Research shows that its hemicellulose breaks down more easily, forming a different spectrum of toasty aromas. Eastern European oak is purchased from both government controlled forests and private land. Although the logs are less expensive, lower yields produce barrels that are about average in cost.

The final oak barrel is not just a function of the tree and its location but also the characteristics used to make the barrel, such as seasoning toasting and the cooperage style. We will be looking at theses influences next month.

Making the barrels

Making oak barrels is divided into a series of steps:

  • Cutting into staves
  • Seasoning
  • Toasting
  • Making the barrel

Cutting into Staves

As mentioned earlier French barrels are low in tyloses, which give the water retaining properties to barrels. It is for this reason that French oak cannot be sawn into Staves (used to create the barrels) but need to be split along the grain of the wood. American oak has much more tyloses and can be sawn across the grain while still retaining its watertight properties. This is one of the main drivers of price. Splitting is slow and requires expensive expertise, while cutting is cheaper and simpler, this makes American oak barrels cheaper.

Seasoning

Before barrel construction the cut/split oak staves must dry out and season. It also allows some important chemical modifications to occur. Tannins are reduced, as are some of the bitter tasting compounds. At the same time there is an increase in some aromatic compounds. Drying staves in ovens is quicker and cheaper, however the chemical changes do not occur. The consequence is that the oak has fewer aromatic properties and more bitter components ready to leach into the wine. Poorly seasoned oak leads to nasty wine!

Toasting Barrels

Manufacturing involves heating barrels over a fire, so they can be bent and shaped. The charring that occurs on the inside is referred to as toasting. The level of toasting that the barrel has determines the toasty flavours imparted in the wine. When used appropriately, the toasty flavours can have a significant beneficial effect on the wine's flavour.

Barrel Making

The Barrel Maker is called a Cooper and is a specialist skill often taught as an apprentice. Oak Staves are shaped and fitted together over heat to soften the wood to bend.

The final barrel and how it will influence the wine is determined by wood selection, age of the tree, which part of the trunk is used, seasoning and the amount of toasting.

Flavours from oak barrels - the technical bit

Lactones are the most important oak derived flavours in wine and are known as oak lactones. On their own the oak lactones smell like coconuts, but in wine they smell oaky too. The two main types are known as 'cis' and 'trans' isomers of B-mthyl-y-octalactone. The seasoning affects the ratio of cis to trans oak lactones and toasting reduces the overall lactone levels. Trans has a coconut aroma, while cis has coconut and earthy herbaceous characteristics. American oak is much higher in lactone concentrations.

Vanillin The component behind vanilla is present in significant quantities in oak. If the oak is actually fermented in contact with oak, the yeast used in fermentation reduces the vanillin concentration. Thus barrel-fermented wines smell less vanilla and oaky even though they are often in oak for longer.. Levels of vanillin increase with mild toasting but can decrease with heavy toastings.

Guaiacol has a smokey aroma and is also described as spicy. It is formed by the degradation of the wood component lignin during toasting and therefore increases at high toasting levels.

Eugenol is a clove-like smell. It increases with seasoning and toasting.

Furfural-5-methylfurful is produced by the heat induced degradation of sugars and carbohydrates during toasting. They have a sweet butterscotch and caramel aromas with a hint of almond.

Ellagitannins Tannins absorbed by the wine from the wood are known as ellagitannins. They modify the structure of the wine and increase the colour of the wine. They have an astringent taste. The concentration decreases at heavy toasting levels.

Many of these compounds occur at levels below their individual detection thresholds in wine. However they can have a synergistic effect on the flavour and aroma of wine. For example, the perception threshold for oak lactones is reported to be 50 times lower in the presence of vanillin. In addition the combination of more than one of these can produce complex flavours or aroma sensations. Whether or not any of these flavours will be positive depends upon the context of the wine. It is a complicated business.

Cutting edge oak and the alternatives

In recent years the use of oak staves, chips and powder has been seen in many cheap wines and some mid-priced wines. The surface area of the wine that is in contact with the oak will increase the flavour extraction for the wood, and staves, chips or powder submerged in the wine increases the surface area considerably. But oak barrels do two things - they impart flavours and allows micro-oxygenation to the wine.

Micro-oxygenation allows incredibly small bubbles of air to pass through the pours of the barrel helping with many of the chemical process going on inside the barrel. Many winemakers are aware of the benefits of micro-oxygenation and have been bubbling oxygen through their stainless steel tanks for a while. With increased surface area associated with chips and micro-oxygenation it is becoming increasingly difficult to tell the difference between the barrels and chips.

The cutting edge with staves, chips and powders has in recent years been the increased understanding of the importance of seasoning. Improvements have been steady and some winemakers can no longer tell the difference between chips and barrels. A well-made wine using chips will be better than a poor wine made in a barrel. Winemakers are increasingly planning to use chips and staves in mid-priced wines, with several premium wines now using the technology.

The use of various oak alternatives at different stages of fermentation and aging with or without micro-oxygenation gives winemakers an enormous range of possibilities for experimentation. There are lots of opportunities to increase quality and decrease price that the barrel simply cannot offer. For example, it is not usually possible to ferment reds in barrels, currently the earliest winemakers can transfer the red wine to barrel is during the final stages of alcoholic fermentation. But oak alternatives can be used during fermentation when it is claimed that they help build the structure, fix colour and reduce green notes.

The benefits of alternatives are:

  • Price - chips and staves cost a fraction of barrels. A typical 225 litre barrel costs £400, adding around £1.30 to the cost of a bottle of wine.
  • Barrels take up space and require expensive racking solutions.
  • Time - barrels require filling, emptying and topping up - all take time and have a labour cost.
  • The quality of alternatives has increased considerably over the last four years.
  • Allows winemakers to experiment with different styles.

While barrels are the earliest piece of winemaking technology, they are a tried and tested way of bringing up fine wines, it seems that for the adventurous winemaker a combination of barrel alternatives with micro-oxygenation promise a range of powerful and cost effective tools to increase the quality of the wine.

As the quality of products on offer increases and more data is accumulated on their use it's likely that oak alternatives won't always be seen as a rather devious short cut for dressing up cheap wines, but increasingly used for premium wines.