Fermenting with oak: what are the benefits?

The benefits of maturing red wine in oak barrels is not a mystery. The flavour compounds extracted from the oak add to the complexity of the wine while ‘hydrolyzable tannins’ are extracted from the wood, improving the ageing potential and smoothing the mouthfeel of the wine. Furthermore, the slight oxidation effect that occurs over time speeds up maturation due to the condensation (polymerisation) of tannins occurring in the wine.

All these chemical interactions that develop red wines into more complex and smooth wines occur happens after fermentation. What happens when you add oak during fermentation? Will it have the same effect?

Flavour extraction

During fermentation, flavour compounds are extracted from the grape skins. When oak products such as oak extract, oak shavings or oak chips are added to the wine during fermentation typical oak flavours such as coconut, vanilla, chocolate and spice will also be obtained. While these oaky notes add to the complexity of the wine in and of itself, it also serves to mask undesirable green characters that might be present in the grape must. Masking green characters are one of the main reasons why winemakers ferment their wines in the presence of oak.

Choosing the right oak product for the right wine is important. A lighter toasted oak product would work better with a lighter style wine such as Pinot noir, as opposed to a heavy toast oak product that might better support a more robust Shiraz.

The presence of yeast cells is another factor to take into account as they can also metabolise some of the oak components, creating different flavour nuances than when the wine comes into contact with wood without yeast cells. In some cultivars, notably South African Pinotage, yeast metabolism produces a roasted coffee smell as a result of the formation of a combination of furfural and 2-furan methanol.

Effects on tannin structure

Another factor to take into account is tannin extraction. During the fermentation process, tannins and anthocyanins (linked to wine colour) are still being extracted from the grape skins and pips. When wood is added during fermentation, more anthocyanidins and proanthocyanidins are formed, which adds to colour stabilisation. Colour stabilisation is one of the primary reasons why winemakers use oak products during fermentation.

Scientists have also seen that tannin polymerisation occurs when oak is added during fermentation, which means that the wine matures more quickly – ideal for getting wines into the market faster.

The big difference

Oak maturation and oak fermentation are applied for different reasons. Winemakers may ferment on oak to stabilise wine colour or to hide green characters in their wine. Fermenting on oak is also an effective way to obtain oak characteristics in a short period for fruity, easy to drink wine styles that need to hit the market quickly. Barrel maturation does a better job at extracting flavour compounds and smoothing over the tannin structure of the wine. It all comes down to what the winemaker is trying to achieve.

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