Is aerating wine just hot air

Does wine need air? Does it taste better if we shake it up in a glass, breathe the bottle, decant it or pour it through one of those new aerating pourers? The short answer is: do what works for you, because the experts disagree. And science now tells us that we’ll taste what we think we’re going to taste anyway.

In The Oxford Companion to Wine, Dr Richard Smart writes, “Another traditional but disputed reason for decanting is to promote aeration and therefore encourage the development of the wine’s bouquet. Authorities as scientifically respectable as Professor Emile Peynaud argue that this is oenologically indefensible: that the action of oxygen dissolved in a sound wine is usually detrimental and that the longer it is prolonged the more diffuse its aroma and the less marked its sensory attributes”.

So there. It’s settled. Let’s flog our decanters, aerating glasses and aerating pourers on eBay. Forget the mumbo jumbo. Open the bottle, pour and drink. Now. For Professor Peynaud it doesn’t get better than the first sip, direct from bottle to glass.

No, no, no counters one of the world’s biggest selling wine authors, Hugh Johnson. In Wine: A Life Uncorked, he pities poor Peynaud for what he missed. Johnson, a great wine romantic, routinely decants almost all the reds and whites he drinks. “People who leap to judgment on the first sniff are simply in too much of a hurry”, he concludes.

Johnson’s drinking mate, Michael Broadbent, Master of Wine, certainly isn’t in a hurry. Broadbent, writes Johnson, places a wristwatch beside his notebook – then times the rise and fall of a fine wine’s fragrance from the moment it’s decanted. Their shared belief that great wine needs air and time to reveal all couldn’t be further from Professor Peynaud’s position.

Wondering if there were any science to either position, I called the Australian Wine Research Institute. Communications manager, Rae Blair, said the institute had no material to offer.

However, sensory research manager, Leigh Frances, recalled an informal test conducted with a panel of wine experts. In a masked tasting they’d been served a range of wines, some decanted and some direct from the bottle.

With only one exception, the tasters couldn’t tell the difference between the decanted and non-decanted wines. The exception was a French wine, riddled with hydrogen sulphide (rotten egg gas). Aerating the wine dispersed the stench of this poorly made wine.

This takes us back to the original reason for decanting. When winemaking was a more hit or miss affair than it is today, wine often contained unpleasant volatile components, including hydrogen sulphide and sulphur dioxide. Decanting, or even leaving wine open for a time before serving, disperses these.

Hydrogen sulphide forms in a “reductive” environment – that is, in the absence of oxygen. It’s part and parcel of winemaking, especially in the dense cap of skins associated with red wine ferments. Winemakers introduce air during winemaking to disperse it.

The introduction of screw caps led winemakers to even greater vigilance against hydrogen sulphide. Because the screw cap creates a more reductive environment than cork, winemakers were forced to be even more attentive. As a result we enjoy cleaner wines.

However, tiny amounts can still appear in some wines, though whether or not we notice depends on our threshold for detecting it. Giving the wine a good splash, by whatever means, generally gets rid of it.

What other nasties might aeration remove? Almost all wines contain sulphur dioxide as a preservative. Again we all have different thresholds for detecting it, and a small minority of people are even allergic to it. Decanting won’t help allergic people. They simply have to seek preservative free wine.

Most people don’t detect the free sulphur dioxide in wine, mainly because our winemakers now measure the required dose fairly precisely. However, winemakers generally give white wines intended for long-term cellaring, notably top-shelf rieslings, more liberal doses. This slowly disperses from the bottle over time. But it can be an astringent element in very young wines. Again, a good splash into a decanter or jug or gurgle through an aerator generally solves the problem.

Decanting delivers one other clear benefit. But it has nothing to do with aeration. Very old red wines throw a harmless but bitter deposit. Decanting in this case simply separates clear wine from the sediment.

But what are the benefits of aeration and time seen by Hugh Johnson, Michael Broadbent and others. Are they all in the mind?

While no one can quantify the benefits, I’d say probably not. Aeration by whatever means probably reduces dissolved sulphur dioxide quickly – a source of irritation to those sensitive to it. It also disperses hydrogen sulphide, though this fault is now rare in Australian wine.

So that leaves the effect of exposure to air over time. This begins as soon as the bottle’s opened and continues as long as we’re drinking it, whether it’s decanted or run through an aerator or not.

For thirty years at Chateau Shanahan we’ve always tasted wines, sometimes decanted, sometimes not, over several days. We splash them into glasses; we refresh the glasses each day; we swirl the glasses; and the ratio of air to wine in the bottles increases daily. Air destroys some sooner than others.

We don’t time the rise and fall of bouquet. But we do see changes over time. The very best wines become more interesting, sometimes for several days. Big reds, in particular, seem to shed their tannic hardness and reveal more of their underlying fruit. Some initially appealing, fruity wines, on the other hand, collapse very quickly.

We’ve also noted in some delicate, aromatic wines that some lovely highnotes apparent on first opening disappear fairly quickly, even when the wine kicks on revealing other lovely flavours. So professor Peynaud has a point.

There’s nothing scientific in this approach. It’s simply enjoying the changing smells and flavours. And the better, longer lasting wines invariable give greater pleasure. We love decanters, too. What could be lovelier than red wine and candle light winking through cut crystal? The wine tastes good before it’s poured.

And if you’d like to see if  those fancy aerators make a difference, there’s a simple, objective triangular taste test you can do. You’ll need a collaborator.

You need to give your collaborator three identical glasses, labelled ‘1’, ‘2’ and ‘3’, and one bottle of wine. Disappear from the room.

Your buddy now opens the bottle and pours direct from the bottle into one or two glasses; then pours through the aerator into the remaining glass or glasses. It doesn’t matter whether there’s one aerated and two non-aerated — it works either way. The important thing is that you don’t know. Your friend should note which glasses contain which wines.

You now return to the room and three three identical glasses, each filled to exactly the same level. Smell and taste the wines. If one wine smells or tastes different from the other two, then aeration is making a detectable difference; if not, it isn’t. You might like to try the test on a range of different wine styles as it might produce different results.

Whether you like the difference is another thing altogether and entirely subjective.

Copyright © Chris Shanahan 2011