Well, a lot of things, many of them having to do with chemistry.
Unlike most wines, age-worthy wines often aren’t much fun to drink when they’re young. These wines have lots of tannin (which feels like fuzz on your teeth) and can taste harsh and bitter when first released to consumers.
Tannins naturally occur in the seeds, stems and skins of grapes, and is also imparted to wine through oak ageing. But that’s not all that’s needed for a wine to age.
A little thing called anthocyanins are also necessary – these are the compounds that interact with the tannins over time, thus softening them into the fruity, drinkable wine it will become.
Another factor that plays a role is climate – a key reason Bordeaux wine is generally much longer-lived than, say, Napa Cabernet. (There are some that can go head-to-head, but bear with me for sake of discussion.) Cool climate wines are higher in acidity, which also helps a wine’s longevity.
In fact, it’s acidity that allows Chardonnay from Burgundy and white wines from Germany to age in ways that their warmer-climate counterparts can’t. Sweet white wines such as Sauternes offer a one-two punch of sugar and acidity that can help them last for decades.
So how to know if a wine will go the distance?
Figuring it out isn’t an exact science, though there are ways to hedge your bets.
One book suggests, if a wine doesn’t list its pH on the label, to call the winery to find this information or, for the really intrepid, using a pH meter at home.
Alternatively, the average consumer could start by targeting wines that are traditionally long lived: red Bordeaux or Burgundy, a Barolo from Italy’s Piedmont region, or even a Napa Cabernet.
Take the time to find out the best vintages in these regions. Identify some top producers as well and use wine reviews to determine the drink dates. If a wine is likely to keep through the milestone occasion you hope to celebrate, then congratulations! Store it will and when time comes to open the bottle, have a backup on hand, just in case!
Want to know more? This story offers a more detailed analysis.