One often reads in wine descriptions
matured for x months in French and/or American oak" or
matured in steel tanks
y months bottle ageing.
What is the difference between ageing in barriques (225 litre wooden barrels) and steel tanks? When must/can a wine mature in wooden barrels? What happens to the wine in the different types of ageing? What is the difference to ageing in steel tanks and what happens during bottle ageing?
Which wines have ageing potential?
Several factors play a role in the ageing of wine:
firstly, the characteristics of a wine, which are linked to the grape variety but also to the growing conditions, such as the alcohol, acidity and sugar content, as well as the phenol concentration
but also environmental conditions such as the nature of the container in which ageing takes place and the storage time
Furthermore, the oxygen content, bacteria and, in the case of bottle fermentation, light, temperature, bottle positioning (horizontal or vertical)
Not every wine is suitable for ageing, i.e. for maturation in barrels. For a variety of reasons, very few of them are, which I will come to in a moment.
White wines or rosés are generally not aged in wooden barrels. They are fermented in steel or concrete tanks, fined, stabilised and then bottled. They are intended to be drunk within 1 to 2 years. This also applies to many young red wines, usually table or country wines, which live from their fruitiness and would lose their freshness over the months or years. This is about 95% of the wines produced. 5% are suitable for ageing.
How can you recognise whether a wine is suitable for ageing? There are various indicators, such as the acidity mentioned above. The lower the pH value (a measure of acidity), i.e. the higher the concentration of acidity, the higher the ageing potential of a wine. The same applies to other indicators such as alcohol content, sugar content and phenol concentration. There are guideline values that the winemaker or oenologist can use as a guide. The Andalusian government commissioned a study in which the following minimum values were determined for the suitability of wines from Mediterranean regions for ageing:
Total Phenolic Index | 60 mg/l GAE (Galic Acid Equivalent) |
Anthocyanins | 800 mg/l |
Tannins | 3 g/l |
pH | <3,50 |
Total Acidity | 4,5 g/l |
Alcohol concentration | >12 vol% |
SO2 | 150 - 200 mg/l |
The addition of SO2 (sulphur dioxide) is important in that it restricts microbial growth, which can have a detrimental effect on the organoleptic properties of the wine.
Let's start with the difficult, more complex part, the ageing of wine in wooden barrels.
Oxidative Ageing
Wooden barrels have been used for centuries in wine ageing, firstly for storage and preservation and secondly for ageing wine. This ageing process can be divided into two phases: oxidative ageing, which takes place in wooden barrels and which we will focus on in this article, and reductive ageing, which takes place in the bottle.
Three parameters play a decisive role when using wood:
firstly, the oxygen in the air that diffuses into the wine through the pores of the wood and interfaces such as bungholes, stave contact points and lids
secondly, the phenol input from the wood into the wine
and finally an enrichment of the wine with flavouring substances from the wood.
The bung-hole, cap-stave interfaces and the contact surfaces between the staves vary from barrel to barrel depending on the design and are difficult to influence or control. However, the wood itself and its properties also play a major role in the oxygen, phenol and flavour input into the wine.
Barrels for ageing wine are usually made of oak, French and American oak. Both woods differ in their structure, with the American woods having larger pores than the French. This has a decisive influence on the oxygen transfer rate (OTR), which is higher in American woods than in the European form, given the same treatment. But what influence does this have on the wine?
The wines develop differently in colour and aroma due to the different levels of oxygen transfer into the wine. Wines with a lower oxygen content develop more stable colour molecules and polymerise more slowly than wines with a higher oxygen transfer rate. They also develop different, more varied and more complex flavours.
Wines made from American oak are richer in tannins and appear more powerful than those made from French wood, which tend to be used for more elegant wines whose flavours would be overpowered by the stronger tannins from American wood. This is why American oak tends to be used for powerful wines such as the Tempranillos from the D.O. LaRioja are used.
However, ageing in wooden barrels (barriques) also has the advantage that polymerised large phenol molecules are deposited over time and settle as a deposit in the bottom of the wine barrel. The barrique therefore also contributes to the clarification and stabilisation of the wine [1].
Another aspect of flavour formation in wood-aged wine is the pre-treatment of the barrels before they are used. In order to shape the barrels, i.e. to be able to bend the staves, they are heated over an open fire. A further flavouring factor is then applied by toasting the barrels over open flames to varying degrees of toasting. This thermally decomposes wood substances such as lignin, cellulose, hemicellulose, etc., whose end products such as furans, volatile phenols, lactones, ketones and aldehydes are then found in the wine. These flavours, among others, are formed during toasting:
vanilla
caramel
cinnamon
Clove
nutmeg
Coconut (American oak)
Dill (American oak)
Smoky notes
chocolate
coffee
Reductiv Aging
As mentioned at the beginning, not all wines can be matured in this way. This method cannot be applied to most wines, which are fermented in steel or concrete tanks and then stored for some time under exclusion of air (reductive) until bottling.
The steel or concrete has no influence whatsoever on the quality of the wines stored in them, so that their fruity flavour from the fermentation is retained. These wines would oxidise in atmospheric oxygen and lose their aroma within a short time.
More and more winegrowers are turning to this ageing method, as these wines do not contain as much tannin as those aged in barriques, are lighter and fulfil the current demand for lighter wines. In addition, steel tanks are easier to maintain and clean than barriques and can be used as often as required. Barriques are generally used 3 times. After that, they have largely lost their ability to pass on their ingredients to the wine. This makes barrique wines considerably more expensive to produce.
Bottle ageing
After being stored in wooden barrels or steel tanks, the wines are bottled. However, this is not the end of the ageing process. Even in the bottle, the wine, be it red or white, undergoes an ageing process that differs depending on the type of wine.
In the case of red wines, polymerisation continues in the bottle until the molecules have reached a critical size, precipitate and accumulate as a deposit at the bottom of the bottle. Other flavour-forming substances also react with each other and form new substances: ketones are formed from aldehydes through oxidation, esters are formed from alcohol and acids, which either have a flavour-forming function themselves or react with other substances to form further flavours, the so-called tertiary flavours. This is an ageing process that increases the complexity of a wine and enhances its quality. Over time, the concentration of flavour-forming substances decreases due to polymerisation or reaction with other substances and the acidity becomes more prominent. This is the point at which the wine has passed its zenith and its quality deteriorates. It is not possible to predict with certainty when this point has arrived, as the ageing process depends on several factors such as temperature, light, size of the bottle, type of closure, initial chemical composition of the wine, temperature fluctuations, exposure to oxygen, etc.
The ageing process of white wines in the bottle is not as well researched as that of red wines, but it is known that the phenol content does not play as great a role in white wines as in red wines, but rather that the acidity and sugar content are decisive parameters for ageing. For example, a Riesling with a low pH value will often keep longer than a Chardonnay, which has a higher phenol content. The barrel ageing of white wines also has a positive effect on bottle ageing.
Classification of Spanish Wines by Ageing Period
Spain is the only wine country that categorises its wines according to age: Joven, Crianza, Reserva and Gran Reserva. The characteristics of these categories are presented below.
Joven
Joven (which is rarely labelled as such, but should still be mentioned for the sake of completeness) is a young wine that is bottled directly and does not mature in barrels like its stronger, tannin-rich contemporaries. The Joven is usually sold in the same year it is bottled.
Crianza
Crianzas mature for a total of 2 years: 6 months in wooden barrels and 18 months in the bottle before they go on sale. In Rioja and Ribera del Duero, Crianzas even spend 12 months in barrels (J. Robinson, The Oxford Wine Encyclopaedia).
Reserva
The red Reservas mature for three years: one year in the barrel and two in the bottle. Reserva white wines mature for 6 months in wooden barrels and then 18 months in the bottle.
Gran Reserva
Red wines from particularly good vintages can mature even longer: two years in the barrel and then three years either in the bottle or in concrete or steel tanks. These special wines only come onto the market in the sixth year after the harvest and are called Gran Reservas. Special white Gran Reservas are aged for 6 months in the barrel and 42 months in the bottle.
References
[1] | National Library of Medicine/Foods - Wine Aging Technology: Fundamental Role of Wood Barrels, Sep. 9. 2020 |
[2] | LWT - Lebensmittelwissenschaft und -technologie 158 (2022) 113113 - Entwicklung von Rotwein in Eichenfässern mit unterschiedlicher Sauerstoffdurchlässigkeit. Phenolische Verbindungen und Farbe. |
[3] | Jancis Robinson - Das Oxford Weinlexikon - Hallwag Verlag, Auflage 5, 2007 |
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