Oxygen and Wine

There is a bit of a love hate relationship between oxygen and wine.

For the most part it is thought that oxygen is a detriment to wine… but this isn’t always true. In fact, the lack of oxygen through some winemaking stages produces lower quality wine.

Aromatic wines like Riesling that are protected from oxygen with a layer of inert gas such as Carbon Dioxide throughout all winemaking stages produce a much more flavourful wine.

However, red wines benefit from oxygen through various stages of wine making.

The yeast will be much healthier in the early stages of fermentation when there is oxygen available. This can be accomplished by slopping the wine around a bit while plunging, splashing while racking, adding air during pump over, sparging through a stainless-steel sinter that emits a fine mousse of air bubbles or even jets of air blasted into the bottom of the fermenting must.

Whilst the colour of red can be turned to brown with bad exposure to oxygen, the colour and mouth feel is actually improved by oxygen during various stages of ferment and maturation.

Anthocyanin is the molecule responsible for the colour of red wine. Over time this molecule settles out causing the wine to be less intensely coloured. However, in the presence of an oxygen molecule this colour molecule is joined to a tannin which stabilises it and prevents it falling out of solution.

Tannin is responsible for the drying tactile sensation of red wine. We talk about mature and immature tannins, when mature the tannins can be fine and velvety. Oxygen assists in this process, as small tannin molecules join together when they can snuggle up with an oxygen molecule. These longer molecules make the wine silkier… The drying sensation of tannin is the result of tannin molecules poking through the mucous membrane in our mouth. When there are a lot of short little tannins floating around they make your cheeks stick to your teeth. When the pointy end of these spikey little guys are joined to another tannin the molecule becomes long and silky… think spaghetti noodle as opposed to a spikey mace ball.

Oxygen is a very small molecule, O2 is the complete formula, it doesn’t weigh much, and it doesn’t occupy much space. It is entrained in the wood of oak barrels and this is in part the advantage of maturing wine in barrels. Over time the O2 finds its way into solution and is quickly scavenged up by an eager molecule in the wine. Wine has limited capacity to be improved by O2, if left in barrel too long the tannins actually lose their silkiness and become very dry or hard. The amount of O2 available to wine is relative to the barrel surface area/wine volume ratio. This is why wines are often moved from small format to larger format barrels if the intention is to age in oak for a considerable period.

Oxygen also assists when tasting wine as it releases flavour and blows off some of the undesirable aromas that may have developed in bottle. Hence we swirl the wine around the glass to mix a bit of oxygen (or if you’re a rude and crude winemaker like me you may cover the top of the glass with the palm of your hand and give it a vigorous shake to rid any persistent hydrogen sulphide… H2S… rotten egg gas).

Bottle aged reds are almost always improved by decanting which introduces oxygen while the wine is poured and by the large surface area in the bowl.

This is a good time to distinguish between evaporation and oxidation:

Oxygen introduced while pouring wine causes the more volatile molecules to vaporise. This can include sulphides and even overt alcohol… this is desirable.

Wine left in a glass overnight will oxidise causing the wine to lose its vibrancy, go brown and take on some unpleasant notes of prunes, bruised apple and often slightly metallic… this is undesirable.

Red wine glasses have a large bowl because the flavours in reds are released more slowly than white wines. Aromatic white wines release their aromas quite readily, hence white wine glasses are narrow.

And don’t forget, if you taste making some really grotesque noises by swishing the wine around whilst sucking in air it will also liberate more flavour.

Now that you have all the tools, enjoy your sophisticated wine tasting. Cheers🍷

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