Wine ages and changes flavors and aromas over time, sitting in wood barrels and then sitting in glass bottles. Brown liquor—distilled spirits like whisky or some rums aged in wood barrels—gains flavor from years-long exposure to wood and the chemistry of time. But conventional wisdom would say that once those spirits hit a bottle, time essentially stops.

It’s true that a bottle of 18-year-old Macallan won’t spoil in your liquor cabinet—in the sense that it won’t become infected by microbes (one thing ethanol is good at is killing microbes). But it turns out that the spirit still changes. "There’s no shelf life because there’s no hazard to health, but flavor changes with spirits over 10-plus years," says Ian McLaren, director of advocacy at transnational spirits giant Bacardi. "It’s not a time capsule."

More than that, the changes can happen faster than most people expect. Last week at Tales of the Cocktail, the annual Comic-Con of booze in New Orleans, McLaren and a team of Bacardi flavor scientists presented some new research that attempted to prove that point. That’s a good thing; booze companies conduct a lot of research into how their products taste, but don’t share it as often as the drinking community might like. At Tales, though, sometimes the curtain gets pulled back. This isn't peer-reviewed, published data, but it's a look at what a big spirits company cares about.

Heat and Light

Extremes of temperature change the flavor of a spirit. In part that’s because temperature can break down a type of organic molecule called a terpene—including family members like limonene and pinene, which smell the way you’d expect from their names. Like any big manufacturer, Bacardi controls for this effect during production, but the company initially didn't control what happened once the bottles shipped.

So over the last decade, Bacardi researchers have taken temperature readings along their entire distribution chain, in cases and then within individual bottles. They found fluctuations of nearly 40 degrees. (Bacardi now ships with coolers and blankets to try to keep temperature more consistent.)

A potentially even bigger problem: light. In another experiment, researchers exposed clear bottles (they call them “flint”) of whisky to ultraviolet light—simulating the sun—for 15 days, and then used a spectrophotometer to accurately measure the color of the liquid. Bourbon lost 10 percent of its color within 15 days. Scotch lost nearly that much in the first 24 hours, dropping 40 percent of its color overall.

The team also took spiced rum in both flint and amber (brown) bottles and exposed one pair to the UV setup and the other to direct sunlight. Regardless of the light source, the amber bottles retained 5 to 10 percent more color over two weeks. The gap widened as the exposure continued.

You’re thinking, who cares what color the stuff is if it still tastes the same? At the panel, the Bacardi researchers showed the magnitude of that problem with a tasting. (At Tales of the Cocktail, nobody leaves a seminar sober.)

They gave every attendee two cups of liquid, one with clear spirit and one with brown. Here are my tasting notes:

1: Not very complex, firewater alcohol style

2: More syrup-y, slightly sweeter

Then they told us what was in the cups: the exact same flavorless, neutral spirit. One cup also had a bit of food coloring.

Nathan Mattise

It’s actually an old trick. In the classic 2001 study "The Color of Odors," taste scientists gave more than 50 wine experts a flight of white wines and a flight of reds and asked them to describe the flavors of both. Most identified typical white-wine flavors in the first set and typical red-wine flavors in the second, despite the fact that they were actually the same wine, with the “reds” colored artificially. Put simply, color matters, especially for flavor.

Air

Even if you stored your booze in a temperature controlled, pitch-black cabinet, degradation would be inevitable—because you opened the bottle. That’s because of oxidation—yes, the same thing that’ll rust iron.

The Bacardi team replicated the effect with gin. We tasted three cups—one kept at 40 degrees for 11 days, one held at 125 degrees, and one exposed to UV, all oxidized. The 40-degree gin tasted fine. The 125-degree gin tasted like cardboard. And the UV-gin tasted less intense and smelled like mothballs. It makes sense that gas chromatography on the gins showed that they lost citrusy limonene but not camphor, the mothball scent. Under similar test conditions, whisky lost the fatty acids that convey creaminess and picked up ethyl acetate notes—nail polish remover. Rum lost ethanol relative to acetic acid, which is just vinegar.

Look, you’re not going to not open your booze. But you can keep air out with stoppers and caps. You can buy smaller bottles for mixers and ingredients that you dole out in fractions of ounces (looking at you, Crème de Violette).

Or you could follow the Bacardi team’s advice: Drink responsibly, but in a timely fashion. It’s probably after 5:00 somewhere, right?