Oak in the Bottle: A Complex and Fascinating Story

The use of oak in wineries is a vast and never ending topic. In order to tackle it, three different cases will be analyzed: that of an inexpensive blended red wine, that of a premium quality white Burgundy and finally that of a chateau bottled Bordeaux. 

 

Oak management in its different forms is part of most winemaker’s work. Since it has an impact on cost production and wine style, its use will vary depending on the market segment the wine will be positioned in. Inexpensive blended red wine producers, premium quality white Burgundy producers and château bottle Bordeaux will all have their own view on this subject. However, all those managing oak will have to take care of common technicalities: oxygen, SO2, Brett, general hygiene management as well as control temperature and humidity in the cellar. This article, after a brief reminder of the various oak types and origins, will first tackle the different options available and then enter into the detail of technicalities involved.

 

Oak types and origins

 

Most oak barrels come from the genus Quercus tree, which can be split into hundreds of species. However, only three are used for making barrels: Quercus alba, Quercus sessiflora (also know as Quercus petraea) and Quercus robur (also know as Quercus pedunculata).

Each one will have a specific origin: Quercus alba is the American oak comes from American forests while Q.sessiflora and Q.robur come from France. The latter comes principally from Limousin, Burgundy and South of France, while the former will come from Centre and Vosges regions in France. Q.robur will offer high extractable polyphenol content and makes wines that are more structured, less aromatic. Q. sessiflora will contribute more aroma and less structure. Finally, Q.alba will offer low phenol content but very high concentration of aromatic substances.

 

Oak in the cellar

 

The options in the use of oak will depend widely on the goals of the winemaker, both regarding style of the wine and the cost and time constraints.

 

For a cheap inexpensive red blend (South Eastern Australia, Gallo entry level wines, red blends from cooperatives in Europe), the key issues to consider in the use of oak are time and cost. The quicker an oak flavor can be imparted to the wine, the better. Depending on the regulation of the country involved (for instance, oak powder is forbidden in the EU while it is widely used in California), one option or another can be used: liquid oak, oak powder, chips and staves.

 

In the case of chips and staves, the type of wood and degree of toasting has to be chosen; besides, chips will have a more pronounced effect on wine than staves since they offer more angles to the wine and thus increase contact with it; both, to a certain degree, will impart oak flavor and improve mouth feel and color stability.

 

For premium quality white Burgundy (Meursault, Puligny Montrachet, Corton and the like), most winemakers are looking for finesse, elegance and balance in the wines. Cost considerations in this case will be less important, so more expensive options can be considered. 228 liter barrels and larger barrels (350, 400 or 500 liters) are the main available options. Other criteria to take into account are cooper, origin of wood, width of staves, degree of toasting, time in wood and desired style among others, etc.

 

As far as degree of toasting is concerned, light toasting is achieved after 20 minutes and 120 to 180ºC; after 10 more minutes, temperature reaches 200ºC giving a medium toast; a further 5 minutes will produce 225ºC a heavy toast. From the lignin in the wood comes the phenolic aldehyde vanillin; other compounds will bring smoky, roasted, spice, clove and others. Compounds derived from the hemi-cellulose produce even different aromas: toasted bred, caramel, cocoa, coffee, sweet pepper, roasted almond … Age of barrel is another factor to take into account: even though they give fewer flavors to the wine, they still allow oxygen exposure and have an impact on the structure of the wine.

 

As far as fermentation in barrel is concerned, white wines in Burgundy tend to ferment in barrel; this operation has a major impact on the structure of the finished wine. Yeasts present in the barrel, coating the inside of the barrel, will reduce contact between wine and wood and then absorb some of the wood extracts turning them into less aromatic compounds. In the end, the wine will be more subtle and harmonious. Besides, yeasts will protect the wine from oxidation.

For example, in Domaine Pierre-Yves Colin-Morey, 80% of the barrels they use are 350 liter

because they give fresher wines with less impact of oak; barrels are principally sourced from Francois Freres and from Chassin because they bring the elegance he is looking for in the wines. However, in Domaine Vincent Girardin uses 228 l pieces for its Meursaults and Pulignys but favors bigger barrels for lesser appellations such as Santenay and Savigny.

 

For chateau bottled Bordeaux, the aim is to sell wines typical of the appellation with a very competitive quality / price ration, that is from 4 to 8 € retail price in France. In order to achieve that, cooperatives (mainly in Entre-Deux-Mers) will use a combination of oak chips, staves and 225 l barrels and make a blend of the wines produced by these different methods; but also big names like Mouton Cadet, Baron de Lestac and others, will do the same.

 

As an example Univitis in Bordeaux, a big cooperative, will mainly use staves and chips (minimum size allowed in Europe of 2 mm) for entry level wines and a combination of the latter with oak barrels for the Château Les Vergnes brand, the top cuvee of the cooperative, with ex-cellar prices of 3,5 – 4 € a bottle.

 

Technical aspects involved in each case

 

All winemakers will have to handle a series of technical aspects in the cellar, whatever their commercial goal is.

 

Oxygen management is something that needs to be taken into consideration whatever the case.

 

For cheap inexpensive red blends and Bordeaux bottled wine: since part or the totality of these wines use chips and/or staves, some oxygen contact might be needed. When it is not brought by the barrel, other means have to be found. Here is where and when micro-oxygenation techniques intervene.

 

The micro-ox objectives during elevage in vats are clarification, stabilization and reduction avoidance. It favors polymerization of tannins and retention of color.

 

As an example, in Union Guyenne (Bordeaux cooperative) examples: in tanks, 10 cc /liter are required for a period of 2 weeks, during which the tannins are softened and more color is obtained, helping the combination of anthocyanins and tannins; the wine will also develop well in bottle. Even if this method is generally used for wines with high tannins and high anthocyanins – thus wines of a long keeping potential – it used here to allow tannins to polymerize and give structure to the wine.

 

In the case of top end white Burgundy, contrary to micro-ox, several operations involving oxygen have to be taken into account.

 

Oxygen is in contact with the wine through the wood itself, through the surface of the wine in contact with air inside the barrel and at racking. It is estimated (Emile Peynaud), that 20 to 29 cm3 of oxygen enter an oak barrel every year. However, exact quantity is difficult to measure since some is consumed by ellagitannins in the oak.

 

Racking (the fact to transfer the wine out of the barrel and put it back again; this can be accompanied by quite a lot of oxygen pick up) is a violent way to introduce oxygen in the wine. The number of times the wine is racked and when it is racked will definitely contribute to define its profile.

 

Topping up it is the action of replenishing the barrels to get a minimum ouillage (head space) protects the wine. Barrels are usually topped up twice a week (dixit Émile Peynuad). A wine of at least equal quality to that present in the barrel must be used to avid spoilage.

Size of the barrel is also a key factor: smaller barrels allow a larger volume to surface area in contact with the oak. Thickness of the staves will also have an influence on oxygen uptake over time.

 

SO2, a powerful antioxidant and antimicrobial agent is used – particularly after Malolactic Fermentation (MLF) transforming the malic acid into the softer lactic acid) – when the wine is in danger of being spoiled because it is unprotected by CO2. In this case, it is a powerful tool against Brett. It is also used when racking the wine.

 

Lees ageing: here frequency of batonnage (lees stirring) and time on lees are two important aspects. This concerns specifically white Burgundy.

 

For instance, at Domaine Roulot, in Meursault, Jean Marc Roulot restricts batonnage to years when the acidity level is high and performs a maximum of 5 to 6 rousings with none at all after the malolactic fermentation. The aim here is to avoid loss of finesse while at the same time adding richness to the wine.

 

Brett avoidance management is also a key issue. It has been demonstrated that Brett (a genus of yeast) that causes problems in the wineries because it brings off flavors to the wine (bandage, medicinal, phenolics, sweaty, rancid, stable aromas) can be found in oak toasted barrels up to 8 mm deep in the staves.       

 

General hygiene is a given, particularly when manipulating wood (chips, staves or wooden barrels), it is key to clean all the equipment used in racking and wine movement inside the cellar; oak barrels (used for Burgundy whites and Bordeaux reds) must be cleaned by steam, boiling water or by submerging them in water to which SO2 has been added; this all the more important when a used barrel has absorbed 5 liters of wine and also the latter will alter itself producing acetic acid.

 

The control of temperature and humidity degree has a direct impact on wine. The effective control of temperature and humidity degree allow an ideal and even aging process rather than an undesirable development of flavors in barrels. Cellars containing oak barrels must be of limited dimensions and closed to avoid ventilation and shifts in temperature.

      

As a conclusion, even if each producer profile will use different options (cheap oak substitutes for inexpensive blended red wine, top quality barrels of different sizes for top Burgundy whites, a mix of cheap options and barrels for bottled Bordeaux), they all have to face common technical issues. These include oxygen, SO2, Brett, general hygiene management as well as control temperature and humidity in the cellar. The way they do it, will have a clear and definite impact on wine style and quality.