Oxidisation of wine is one of the most common of wine faults (less so now that we use screw caps as opposed to cork seals of the past).
But that said, isn’t oxygen good for wine? What about everything we’ve learned about introducing air to the glass (swirling of the wine) to bring out all its deepest, darkest aromas?
Like anything else, too much of a good thing can lead to a demise — yes, even for your favourite bottle.
It’s true – wine does need oxygen. The whole “let the wine breathe” phrase isn’t nonsense. Introducing oxygen to a newly opened bottle of wine or a freshly poured glass (hence, why we decant and swirl) is beneficial. Oxygen allows the aromas in wine to become more present, making it easier to identify what exactly you’re smelling.
The moment that wine encounters oxygen, it begins to open up.
Introduction of oxygen also softens the mouthfeel of wine; this is due to the breaking down of tannins, the cause of that slightly harsh, dry sensation you may feel along your cheeks and tongue. This practice is extremely beneficial in young reds, especially cabernets whose bright acidity and gripping tannins can seem austere and unpleasant at first.
However, too much oxygen leads to oxidation. This can happen during the actual winemaking process or even after the wine has been bottled. Two components of wine, anthocyanins and phenols, are very susceptible to oxidation – all oxygen needs is a catalyst for the reaction to occur.
So what’s the chemistry??
(yup, I completed a BE in Chemical Engineering at Sydney University many moons ago…!)
In simple terms, oxidation is a staged reaction:
Ethanol -> Acetaldehyde (smells like green apples) – > Acetic Acid (vinegar)
So how do I know if my wine is oxidised?
The wine may be slightly brown in colour, with little or no fruit aroma and a lacklustre palate, potentially displaying notes of vinegar. It may have a woody, toffee-like smell to it.
Bright red colours will have turned brownish-orange. Fresh tastes develop drier, more bitter characteristics. The wine’s pigmentation will have decreased and there will be a corresponding loss of aroma and flavour. And a bad case of oxidation will cause even a white wine to turn brown.
Think of an apple or banana that’s been sliced and left out; the abundance of oxygen causes the flesh to brown, the aromas to dissipate and the flavours to disappear. Wine is no different.
Incidentally, white wine is much more susceptible to oxidisation than a red, because reds have higher tannin levels which act as a buffer.
Last but not least, once a wine is oxidised, the only place for it is in the sink – oxidisation cannot be reversed.
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