It looks great, of course, but why does size matter when it comes to ageing wine? It all comes down to oxygen.
The role of oxygen
Oxygen - a necessity for life for you and me, but also for your precious wine. The exposure of the grape juice to oxygen during winemaking can make or break the wine and is a key component of its style. Once the juice is in the bottle, the glass is inert and the oxygen exposure is halted until you open it up to pour a glass. Almost. A natural cork, as you probably know, isn’t completely air proof. The small exchange of oxygen through the cork is a key to ageing wine.
The oxygenation through a cork is technically referred to as nano-oxygenation because of its minute nature. The oxygen that enters interacts with chemical compounds called phenolics in the wine - tannins and many flavor compounds included. The slow oxygenation during ageing will reduce the wine’s astringency, integrate the flavors of the wood, soften the tannins and release all new flavor compounds. The majority of white wines do not benefit from ageing in the same way as red though there are numerous exceptions.
Slow ageing is key to complexity
The experience is that the slower the wine ages, the more complexity and nuance it adds. The key concept is ullage - the amount by which the bottle falls short of being full. The ullage in a magnum gives a similar surface-to-air ratio as in a regular bottle but the volume of wine that is available to absorb the oxygen is of course twice as large. With the reduced oxygen exposure, the wine can keep its freshness and fruit flavors longer too.
Magnums tend to be a bit more expensive than two regular bottles of the same wine as the materials and handling are costly. The glass is thicker which adds weight but also offers somewhat more protection against light and temperature variation. Magnum corks are produced just like regular corks and generally keep the same quality, but as the really large bottle formats are usually produced for special occasions only they will have hand cut corks which may not be as exact in keeping oxygen out, increasing the risks to the wine. Not to mention that a tainted cork will ruin your entire bottle regardless of if it is 37.5 cl or 300 cl.
The drawback with Magnum - too little time!
Magnums can be trickier to store, they take their fair share of space in the wine cellar. But the big problem is the same as the big advantage - they age slowly. So slowly, in fact, that they might not be your best bet.
I have often found myself a bit quizzical at trade tastings where we have tasted older vintages from magnum. Colleagues have happily quipped that 30-year old bottles taste like much more recent vintages. My thought has always been that, with limited space in my wine cabinet, I’d rather have a wine develop at a pace so I’m able to enjoy it while I’m young enough that my taste buds are intact.
If I want the freshness of a recent vintage, I’ll just go buy a recent vintage! Who knows what I’m drinking in 30 years or if I’m even drinking at all. Not sure if this is me being boring or practical. But I’m not alone. As the queen of the wine world, Jancis Robinson, wrote “there is really only any point in paying extra for a big bottle if you are probably too young to afford one.”
As most wines available in a magnum size or larger are premium red wines with lots of structure, often in the form of tough tannins, they need time to soften, open up and gain complexity. The same wine will be enjoyable to drink earlier from a regular 75 cl bottle than in a magnum (though logically, it will peak earlier too!).
So unless you are buying champagne or magnums that have already been aged, consider when you want to enjoy your bottle. If it’s in a few years, you might be better off with a normal size. Planning on letting the kids inherit the cellar? Go big.