Drinkers of both wine and whiskey (and other spirits) must have considered the cork paradox at some point. Here it is: Wine corks dry out, so collectors must store bottles on their side, in order to keep the cork wet and, thus, intact. But spirits are known to damage cork material, so whiskey and other spirits must be stored upright. However, many whiskeys are sealed with cork stoppers, and many of these spirits — especially prized dusties — are held on to for decades. So why don’t the corks in whiskey bottles dry out?

First, to counter the obvious: Yes, whiskey corks do get brittle and break sometimes, but this is actually pretty rare. I’ve only had to replace three or four corks in my collection over the last 20 years, and some of those were because the glue connecting the cork to the stopper failed. Brittle corks that crumble into your whiskey happen, but it’s quite uncommon.

So: Why?

I put the question out to a number of industry experts and got the best response from Ewan Morgan, Program Director for Diageo U.S. He says, “Wine is famously stored horizontally in a cool, dark location and this angle is to ensure that the cork never dries out as the wine slowly matures and ages in the bottle but it’s a very different story for whiskey or any ardent spirit which is already matured or ready to drink. Whiskey should always be stored upright as opposed to the accumbent resting angle of Wine. Whiskey, like wine, should also be stored in a cool, dark location (59-68F) to avoid the sun’s UV which can degrade flavor/abv/color and fade the labels. If the bottle is on its side the higher ABV will start to degrade the cork at an exponential rate and the structural integrity will be at risk and you may end up with a very expensive leak.”

It’s not just degrading corks, by the way. Alexandre Gabriel, Master Blender and Owner of Maison Ferrand‘s France & West Indies Rum Distillery in Barbados, notes, “It must be possible for a cork to be capped and uncorked manually by a consumer, so the effort involved should not be too great to allow the bottle to be uncorked without damaging the cork. For example, for a bottle with a corking diameter of 18.5mm, a wine cork will have a diameter of 24mm, while a spirits cork will have a maximum diameter of 20mm. This low tightness on a cork for spirits explains in part why the bottle should not be laid down.”

Morgan continues to the meat of the question, saying, “Why don’t whiskey corks dry out? It’s due to volatility of the alcohol vapor inside the bottle which is a side effect of the strength of the spirit. In effect you’ve got a constant gentle, circulation of moisture bathing the cork and slowing down the shrinkage.”

So, to summarize: Wine is bottled at a low abv, and the amount of alcohol vapor inside the bottle is very small. Whiskey and other spirits, with their 40% abv and up, have a headspace that is full of alcohol and water vapor, thus keeping the cork moist even though it’s stored upright.

Morgan was careful to note, however, “Does this mean the corks in your vintage collection will last in perpetuity? The answer sadly is no. I’ve been buying and collecting vintage spirits for over a decade and can’t tell you how many times I’ve had a ’30s or ’50s era cork collapse and disintegrate as soon as I’ve tried to open them, though they were still very drinkable however after carefully filtering. I recall one bottle I once had to photograph (a 157 year old bottle of Scotch bottled in 1850) that had its cork drop into the bottle during transportation before selling for a then world record price.”

So what do you do if you acquire a cork-stoppered dusty? Should you replace the cork with something else?

Morgan first addresses sealed bottles that have never been opened, such as those being collected for eventual resale: “The best advice I can give here is just leave it unless you have a noticeable leak or a structurally crumbling/withering of the cork. In that case, the best bet is to use parafilm (wax and polyolefin based elastic tape) to securely wrap around the top of the bottle. It’ll help stop oxidation and any further evaporation. I’d strongly advise against replacing the cork unless it’s critically necessary as you’ll devalue the bottle exponentially the second you open or de-foil it (remove the metallic enclosure). Collectors always want everything original.”

And if it’s one you’re drinking? “If the plan is to drink the liquid and never trade or sell it then the rules change completely as you’re going to open the bottle,” he says.” To help counter the effects of oxidation some choose to decant the whisky into smaller bottles as it diminishes with each glass, typically with new corkwood or modern synthetic cork as a stopper. Fastidious collectors have been known to inject the headspace (the air between the liquid and the cork) with inert gas, like argon, to stall oxidation and some people even use glass marbles to raise the level of the spirit as they slowly deplete it over time.”

In other words: There’s no harm in replacing your cork if anything seems amiss. I keep a drawer full of stoppers of various sizes as an insurance policy against just such an occurrence.

Of course, fear of corks drying out — even if it’s rare — has led some producers to move away from cork, just as it has in the wine industry. Mark Simmonds, master blender at Broken Shed Vodka in New Zealand, uses Diam, a blend of natural and synthetic cork as a stopper, which he believes solves the dry-out issue.

“We did a fair bit trialling with cork material, both natural cork and synthetic,” he says. “We initially bottled with a synthetic material stopper cork with wood top. When we were starting to plan to export I felt we needed a better material to handle the challenging and varied climatic conditions often encountered. We settled upon using Diam cork material. Diam is the pre-eminent cork material manufacturer to the wine and spirits industry. It is not 100% cork material – it is a blend of natural cork and synthetic material. It compresses well giving a tight seal and the synthetic effectively seals the cork material from contact with product – so no tainting/corking or drying.”

So, perhaps some good advice there, too: If you are replacing an old, natural cork, a synthetic stopper may do a better job over the long haul (particularly if it’s one you’re frequently removing and replacing, which can cause natural cork to crumble more quickly).