Jamie Goode: Does decanting work or not?

One of the great traditions of red wine service is decanting. It’s the practice of opening a bottle that has been standing upright for some time, and then carefully, in one continuous motion, transferring the wine into another container, typically a clear glass decanter. In the past, when wine was either an elite drink or a commodity, this act was reserved for the elite end of the market. Here, red wines would traditionally be aged for many years to soften their tannic structure. During this ageing process, they would typically throw a sediment: gunk that accumulates through the precipitation of tartrates and also various tannin complexes that have fallen out of solution. If someone tried to pour the wine directly from the bottle, then after the first few pours the wine would become cloudy as the sediment that had gathered at the bottom of the bottle was agitated. And the last couple of pours would be more-or-less undrinkable, with gritty sediment in suspension. So in a fancy country house, the butler would head down to the cellar in the morning, and stand the dinner bottles up. Then, in the evening, they would be decanted carefully before taking upstairs for serving. The elaborate way of decanting is to use a decanting cradle and a candle so that you can see when the first sediment is coming out, and then stop pouring into the decanter. This sort of decanting-to-remove-sediment is incredibly practical and still useful today when dealing with older traditionally made wines, but perhaps not for the very oldest wines, for reasons we’ll come to later.

Most red wines drunk these days have no sediment in them. It’s very rare to encounter a bottle with sediment, partly because of steps in modern winemaking processes such as filtration and fining, but more significantly because almost all red wines are drunk young, and even fancy Bordeaux tends to get drunk young enough that it hasn’t thrown much in the way of a gunky deposit. So decanting to ensure the wine pours clear and sediment-free is a niche activity reserved for quite old bottles.

What are the other reasons for decanting? Most decanting these days is done for the reason of ‘opening up’ a tighter young wine. This is where we get into the topic of wine aeration. Aside from a traditional decanter, you can also buy a range of devices designed to aerate the wine as it is being poured, some of which are quite elaborate. That’s not to mention the two devices with magnets in them that claim to change the tannic structure of the wine, something that even sensible and seemingly intelligent people were convinced about, although there no scientific reason to put wines in a magnetic field. Think about it: if magnets changed the character of the tannins in a red wine in a positive way, then surely most wineries would be using them, as this would be a much quicker and cheaper way of improving red wine structure than extended elevage. And while we might be impressed by seeing magnetic power in action on things that are actually magnetic (Whoah! Invisible forces!), consider this: when you go for an MRI scan you experience insanely strong magnetic fields but come out unchanged! Put a bottle of wine in an MRI scan and I’d bet a lot of money it wouldn’t be changed, and this is a magnet vastly stronger than anything in these wine ageing devices.

Back to decanting to open-up closed red wines. What is happening scientifically? Basically, you are exposing the wine to air, which contains oxygen. Wine can only take up a certain amount of oxygen (the exact amount depends on temperature), and then once the oxygen is dissolved in the wine oxidation reactions will begin. This is where we have the clash between science, experience and expectation. No one has really looked at the science of the flavour chemistry in decanting, but lots of people have made claims about what goes on phenomenologically. Oxidation reactions have been studied, but not at the time scale involved in a typical decant.

The popular notion is that a young red wine, particularly one destined for long ageing, needs decanting to unfurl – to release its aromatic potential. I quite like decanting in this sort of situation: after all, what have you got to lose? A robust young red wine isn’t going to suffer from a little oxygen pick-up over the course of an evening, and intuitively it seems that the act of decanting might well help open it up. But does it? When we decant, we never do the control, so we can’t really say. We may experience the wine opening up, but this could have happened without decanting, and over the course of an evening we change, never mind the bottle of wine. Now an overnight decant, or a double decant the morning before a dinner, might be expected to have some effect because there’s time for oxygen to have some effect even with a young wine. But for a young wine decanted and then served over the course of a dinner, it isn’t easy to come up with a good scientific explanation for how the wine might be opening up chemically. One study from China used a liquid chromatography/mass spectrometry method that could look at changes in organic acids and polyphenols simultaneously, and they applied this to decanted wines. They showed that the levels of most of these 20 compounds were decreased by decanting. But wouldn’t they also be decreased by pouring wine into a glass and letting it sit a while?  

Another study from Australia showed a reduction in alcohol levels in pre-poured wines in a competition setting. Reducing the alcohol will release some of the aromatic components in a wine: studies have shown that rising levels increasingly bind wine aromas. This could be one explanation for the effect of decanting on wine aromatics, but studies would need to look specifically at how much decanting reduces alcohol by.

There is, of course, the psychological impact of the act of decanting. It can elevate the way we feel about the wine, and this in turn can affect our perception. Imagine serving guests a modern young claret: if you take the bottle and decant it, and then serve it in a fancy glass, it increases the chance of this wine being seen favourably by the table.

Some old wines are best not decanted, though, even if they are likely to have sediment. A good way to serve an old wine is to open the bottle, leave it for a while, and then take a taste. If it seems fragile and the aromas quite delicate, then pour from the bottle. There is potentially a lot to be lost from a delicate old wine by decanting it. It should not be the default action for such wines.

And what about whites? Not many people decant them, but I know many people who think that serious whites with some bottle age, or even younger naturally made whites, stand to benefit from decanting. I like this idea.

Still, there is a lot of mythology around the whole practice of decanting and aeration, and few studies have looked carefully at this. Often people do side by side comparisons that aren’t blind, and this is a bad idea. The power of suggestion can influence perception, even if we are experienced tasters. Triangle studies blind are the way to go: if you can’t spot the odd wine out, then your opinions in this case don’t mean anything. This keeps us honest. One study has looked at the impact of fancy aerators on wine, but in a significant way. For his MSc thesis at Cornell, David Brandley examined the effect of the Aervana Luxury Wine Aerator and the Vintorio Omni wine aerator on a red wine. By using a triangle test with experimental subjects, he showed that there was no significant difference between the treated and untreated wines for both devices. All we need now is someone to do the same study with decanting.

• Jamie Goode is a London-based wine writer, lecturer, wine judge and book author. With a PhD in plant biology, he worked as a science editor, before starting wineanorak.com, one of the world’s most popular wine websites.