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The question
I store my wine in a large, cool, walk-in closet but the space is pretty dry. If I'm storing bottles on their sides, do I need to care about humidity?
The answer
Yes, at least if you're in the game for the long term. The "sideways" trick doesn't spare your wine from the ravages of dry air. Besides cool temperature – ideally in the neighbourhood of 13 C, or 55 F – you'll need lots of moisture in the room to prevent wine from evaporating through the cork, with air seeping in to fill the void.
Your first concern is to prevent dry cork, which will shrink and lose its seal, permitting too much corrosive oxygen to prematurely spoil your wine. Yes, laying bottles on their side helps prevent shrinkage, but even a plump cork presents a problem.
Most wine experts overlook another part of the physics equation and the bigger reason why humidity is so important. It has to do with the humidity differential between the inside of the bottle and the outside air. Cork is porous, which is why wine can soak into it in the first place. In other words, it's not a perfect seal even when it's wet. As long as the relative humidity outside the bottle measures less than 100 per cent, wine will tend to seep through the cork toward the drier external environment.
You may have read that the generally accepted relative humidity level for a cellar is about 75 per cent, and that's the number I'd recommend if you can manage it. Why not 100-per-cent? For one thing, it's impractical because at that level you'd have condensation and it would essentially be raining in your cellar. Also, many people would argue that some air ingress helps wine to mature with grace, though I know experts who would debate that point. The more urgent reason to keep humidity down to around 75 per cent is that, at higher levels, mould would quickly form on the corks as well as the labels, tarnishing the appearance, if not also the quality, of your trophies.
The Flavour Principle by Lucy Waverman and Beppi Crosariol (HarperCollins) won the top prize for best general English cookbook at the 2014 Taste Canada Food Writing Awards.
E-mail your wine and spirits questions to Beppi Crosariol. Look for answers to select questions to appear in the Wine & Spirits newsletter and on The Globe and Mail website.