Do natural corks add woody flavors to wine bottles stored on their sides?

Dear Dr. Vinny,

Does natural cork add woody flavors to wine, especially bottles stored on their sides for many years?

—James, Wichita, Kan.

Dear James,

This seemingly simple question actually has a complicated answer.

First off, I have to acknowledge the flaw in the room. Natural corks are one of the ways a chemical called 2,4,6-trichloroanisole (TCA for short) can make its way into wine. It’s not harmful, but it is super potent, and even a few parts per trillion can add musty, wet cardboard notes to a wine and make it unpleasant to drink. At extremely low levels, TCA may not be very noticeable as an unpleasant smell, but it can still mute the desirable flavors and aromas of the wine.

We also know that corks can let small amounts of oxygen into a bottle of wine, especially during the first few months after bottling, as the compressed air trapped in the cork slowly escapes. After that, corks can let even more, undesirable oxygen into the bottle, especially if they dry out. That’s the reason we store wine bottles on their sides—to make sure at least the part of the cork that is inside the bottle is kept moist as a protection against leakage and premature oxidation.

Outside of these two directions, there is reason to believe cork can impart flavor into a wine, but at a very low level. The challenge in talking about this phenomenon is that when you get into the sensory analysis, it’s harder to describe and come to a consensus on a topic. After all, my spouse and I can’t agree if a candle smells good. How are we supposed to agree if one wine has miniscule amounts of cork influence vs. another?

Scientifically, I can explain it like this: Natural corks are made from the bark of the cork oak, Quercus suber. We know that corks contain phenolic compounds—tannins and polyphenols—similar to those found in oak barrels. Over time, tiny amounts of these compounds could be expected to leach from the cork into the wine, just as a barrel-aged wine can take on oak tannins—though obviously, you’d expect a much lower impact because the surface area of the cork compared to the volume of the wine in the bottle is so small.

It’s also worth considering that if a wine has been aged in oak, any additional wood tannins or other phenolics that get added from the cork will almost certainly be negligible compared to the impact the oak barrel has already had on the wine.

Scientists have identified compounds that form when phenolic compounds from natural corks slowly migrate into wine and react with the wine’s own phenolics. Even at low levels, those cork phenolics can react with compounds already in wine, like catechins and malvidins. When they combine, they form bigger, more stable molecules. They are given the adorable name “corklins.” And they can form even if a wine isn’t stored on its side.

Pros of corklins are that larger molecules can help stabilize color and perhaps even soften the astringency of a wine over time, which some might find desirable. I’ve read that some Champagne producers are now doing secondary fermentation under cork (and not crown caps, like you see on beer bottles) specifically to get these corklins into their bottles.

But the con of these molecules is that they could impart a slightly woody flavor. I’ve certainly talked with winemakers who do not like what they perceive as an extra woody note in their wine from these pesky corklins—but overall, it’s not something I would worry too much about. And it’s certainly not a reason to store your bottles upright in the long term. The risk of corks drying out—which will almost certainly ruin your wine—is much greater than the risk of corklins.

—Dr. Vinny