You probably know that vermouth is an ingredient often used in classic cocktails like the Gin Martini and the Manhattan. Unfortunately, during the bad old days of cocktail making, bartenders too often left the bottles to sit on bar shelves for weeks or even months. When the dusty tops were finally screwed off, the vermouth inside was at best lifeless and bland; at worst, it had already begun the slow transition into vinegar.

As carefully-made cocktails came back into vogue, so did bartenders' attention to properly storing and caring for ingredients. I've seen bottles of Carpano Antica (a very nice Italian vermouth) vacuum-sealed after each use and stored in a dedicated vermouth refrigerator. I've seen cocktail geeks argue that the aromas from fresh vermouth dissipate within hours of opening and advocate only buying half-bottles.

I've even explored the topic myself and recommended a process of pouring vermouth into small bottles and then topping the bottles off with inert gas.

But to be completely honest, I never scientifically tested those methods.

Here's why: running a taste test of vermouth storage methods takes a long time and a lot of vermouth. I had never been in a position to "age" a dozen bottles preserved in different ways. Luckily, Serious Eats has my back, and with the support and advice of fearless myth-debunker Kenji López-Alt, I set out to design and carry out an experiment to establish once and for all the best way to preserve vermouth at peak quality.

What Makes Vermouth Go Bad, Anyway?

There are a few different factors that can cause good vermouth to turn nasty:

Microbial Spoilage. Bacteria and mold like to live in moist environments where plenty of food (sugar) is available. Luckily, the alcohol and aromatic herbs used to produce vermouth help to fight microbial growth, but not so much that bad stuff couldn't grow eventually. In most cases, acetic acid bacteria will be the primary culprit: these guys digest the alcohol in wine and slowly turn it into vinegar.

Oxidation. Oxygen reacts with esters, terpenes, and other volatile aromatic compounds responsible for light, fresh, fruity, and floral flavors found in wine.1 Compounds that lose electrons and bind with oxygen are called reducing agents. These include phenols (often derived from the skins, stems, and seeds of wine grapes) which are responsible for some of the astringency and color of red wine. Since red wines are high in these phenols, red wines are more able to weather oxidation without harmful effects. Since vermouth is almost always made with a white wine base, it's particularly vulnerable to oxidation.

Loss of aroma. This one's pretty straightforward. When you pour vermouth out of a bottle and replace the liquid in the bottle with air, volatile aromatics escape from the remaining wine and fill the headspace, leaving your remaining vermouth slightly less aromatic.

I've come across three rational-sounding ways to combat these problems:

Refrigeration. Cold temperatures slow down many physical and chemical processes, sometimes dramatically.

Inert Gas. If oxygen is the culprit behind oxidation, why not replace it with inert gases like argon or nitrogen? That exactly what the product Private Preserve does and a Wired review of multiple wine preservation techniques showed that it works well for preserving wine for up to a week. How does it do with vermouth for a month? That would be my question.

Rebottling. Inert gas can replace oxygen in the bottle, but still leaves the problem of headspace. If, however, you pour leftover wine or vermouth into a smaller bottle with little to no headspace, you'll protect the wine from oxidation and from losing its aromatics.

I didn't bother with vacuum systems. It's very difficult to suck such a hard vacuum on a bottle that oxidation really becomes less of a problem. Plus, the less wine left in the bottle, the more vacuum you'd need. On top of all that, vacuuming vermouth will actually suck even more of its volatile aromatics out than if you just let the wine sit.

With all the background in mind, I set out to create a test of the three most promising storage methods.

Experiment #1: Does Refrigeration Work?

On April 1st, 2014 I bought four bottles of Dolin vermouth (two rouge, two dry) and started an experiment to see what a month in the fridge would do to the vermouth's flavor.

Here's how I set up my test:

Test #1: Dolin Rouge, unopened, refrigerated vs. Dolin Rouge, half-empty bottle, refrigerated

Dolin Rouge, unopened, refrigerated vs. Dolin Rouge, half-empty bottle, refrigerated Test #2: Dolin Rouge, unopened, refrigerated vs. Dolin Rouge, half-empty bottle purged with inert gas, refrigerated

Dolin Rouge, unopened, refrigerated vs. Dolin Rouge, half-empty bottle purged with inert gas, refrigerated Test #3: Dolin Rouge, unopened, refrigerated vs. Dolin Rouge, rebottled into small bottle with no headspace, refrigerated

Dolin Rouge, unopened, refrigerated vs. Dolin Rouge, rebottled into small bottle with no headspace, refrigerated Test #4: Dolin Dry, unopened, refrigerated vs. Dolin Dry, half-empty bottle, refrigerated

Dolin Dry, unopened, refrigerated vs. Dolin Dry, half-empty bottle, refrigerated Test #5: Dolin Dry, unopened, refrigerated vs. Dolin Dry, half-empty bottle purged with inert gas, refrigerated

Dolin Dry, unopened, refrigerated vs. Dolin Dry, half-empty bottle purged with inert gas, refrigerated Test #6: Dolin Dry, unopened, refrigerated vs. Dolin Dry, rebottled into small bottle with no headspace, refrigerated

I designed the tests so that Test #1 and Test #4 would be a sort of "negative control." That is, I figured a half-opened bottle of vermouth, even refrigerated, would taste obviously bad after sitting exposed to headspace for a month. After I established what "bad" tasted like, I would compare the bad stuff to the intentionally preserved vermouth.

One little problem.

After a month, I couldn't tell the difference between fresh, unopened vermouth and a half-empty bottle that had been sitting in the fridge.

Just to be clear, I set this up as a triangle discrimination test. I asked my wife to pour an ounce of fresh vermouth into two glasses and an ounce of the opened vermouth into a third. I then tasted all three without knowing which was which. I tasted all samples at room temperature to better sample the aromatic qualities of the wine.

When I couldn't even guess as to which one was different during the first test, we did the test again, with the glasses in a different random order. And then again. Each time, I had no clue and my guesses at which glass held the opened vermouth were no better than random guessing.

To be complete, we continued the testing with all 6 versions of the test. At the end of it all, I had found zero difference between any of the test conditions.

Conclusion: Refrigeration is plenty effective for vermouth storage up to one month. If you're going to finish your vermouth within a month, as long as you keep it in the fridge, you're good.

Experiment #2: What happens at room temperature?

After coming to terms with my unexpected results from experiment #1, I sent Maggie and Kenji an email that basically went like this:

Hey, turns out vermouth stays perfectly OK in the fridge for up to a month. Kind of awesome news, but super-boring article material."

So together, we decided to take it up a notch.

Many home cocktail enthusiasts face a similar problem: we know we should keep our vermouths and aperitifs in the fridge, but we just don't have enough fridge space. Is there any way to keep vermouth tasting good while out of the fridge?

This time, I took the negative control a step further: instead of simply leaving a half-empty bottle of vermouth to sit, I poured 2 ounces from the half-empty bottle every two days and then poured it back in. This pouring simulated real-world conditions (in the real world, we drink our vermouth and don't just let it sit!) and helped accelerate the cycling of oxygen into the bottle, which I assumed would accelerate the effect of oxidation.

I did the same thing with the bottle of vermouth I treated with inert gas: every two days, I poured two ounces out, then poured the two ounces back in and purged the half-empty bottle with inert gas.

For the case of vermouth rebottled into a smaller bottle, I didn't do the pouring in and out step—the idea behind rebottling vermouth is to let it sit undisturbed until you need to use it. For example, I might pour a 25-ounce bottle of sweet vermouth into two smaller 12-oounce bottles. But here's the question: If I refrigerate and use the first small bottle and leave the other bottle in the pantry, is my unrefrigerated bottle still good after sitting at room temperature for a month?

This time, I stuck to sweet vermouth to cut down on the number of tests. (Serious Eats gave me a sizable vermouth budget...but not that sizable.)

Here's how it all went down:

Test #1: Noilly Prat sweet vermouth, unopened vs. Noilly Prat sweet vermouth, half-empty bottle at room temperature

Noilly Prat sweet vermouth, unopened vs. Noilly Prat sweet vermouth, half-empty bottle at room temperature Test #2: Noilly Prat sweet vermouth, unopened vs. Noilly Prat sweet vermouth, half-empty bottle, purged with inert gas and kept at room temperature

Noilly Prat sweet vermouth, unopened vs. Noilly Prat sweet vermouth, half-empty bottle, purged with inert gas and kept at room temperature Test #3: Noilly Prat sweet vermouth, unopened vs. Noilly Prat sweet vermouth, rebottled into small bottles with no headspace and kept at room temperature

Noilly Prat sweet vermouth, unopened vs. Noilly Prat sweet vermouth, rebottled into small bottles with no headspace and kept at room temperature Test #4 (bonus round!):Noilly Prat sweet vermouth, half-empty bottle vs. Noilly Prat sweet vermouth, half-empty bottle, purged with inert gas and kept at room temperature

This time, I met up with some friends at Heritage Restaurant in Richmond, VA and recruited two bartenders as well as two random bargoers for the tasting. (One of the random bargoers turned out to be pretty well-versed in beverage tasting himself, but that was a lucky accident.)

In the end, we had a panel of seven judges, though one person bowed out after two rounds of tasting. All the tastings were conducted blind: I poured my samples into coded small bottles before we had the event, so all the bottles appeared the same. Respondents also received worksheets that directed them to sample the vermouths in differing orders.

The Results

In the triangle test, participants received three samples. Two of the samples were identical (they contained brand-new Noilly Prat sweet vermouth) and one of the samples was the test condition (either from the half-empty bottle, the purged one, or the one that was rebottled into a smaller bottle). Participants were asked to choose which sample they thought was different. Different, but not necessarily better or worse. I didn't tell the participants whether the odd-one-out would be the older vermouth or the new bottles. Participants instead could write open-ended comments about each round of tasting.

Half-Empty Bottle: 57% correctly identified

Tasters commented that the sample from the half-empty bottle "tasted more bitter than the others", and some called it "oxidized." One mentioned that telling the samples apart "was easy," though another said "they all taste the same."

Inert-gas-purged Bottle: 28.6% correctly identified

In this round, tasters said the samples were "hard to tell apart" and "they all seemed similar." One said the purged sample was "definitely different, but not necessarily better or worse" while another said the purged sample "was more bitter" with a "thicker mouthfeel."

Rebottled in small bottle: 50% correctly identified

(Note: one of my tasters dropped out after the second round, so 50% means that 3 out of 6 tasters correctly identified the rebottled sample.) In this round, tasters mentioned that the rebottled sample was "bitter" and "more sour/bitter."

Purged vs. Not-Purged: 33% correctly identified

While a few tasters commented that the choice they picked tasted more bitter or had less aroma, only people who chose wrong left comments in this round.

What We Learned

Based on statistics, we would expect that 33% of the tasters should be able to correctly identify the test condition by random chance alone. That means that the vermouth purged with inert gas was statistically indistinguishable from fresh vermouth. Then again, tasters had a similarly hard time distinguishing between a bottle of vermouth that had been purged and one that had been left to sit. If I had to guess, I would say that people had more trouble with the final test simply because they had tasted too much vermouth and their taste buds were overwhelmed, but that's just a guess.

Science is always tricky, and my results were far from unanimous in each case. I think, though, we can extract a few useful takeaways:

Refrigeration works pretty darned well. I wish I could go back in time and set up a more rigorous experiment, but I honestly thought I would be able to tell the difference in opened vs. unopened vermouth in just a few days time. Since a month made no difference to me, my hypothesis was obviously shattered.

Vermouth stays drinkable longer than wine does. Most wine lovers would agree that leaving a bottle of wine sitting on the counter for more than a day or two, let alone a few weeks, would mean having to scrap the bottle. And yet, after a full thirty days at room temperature during which I repeatedly opened a bottle of vermouth and exposed it to the air, still only four out of seven tasters could accurately identify the aged sample.

Inert gas works better than rebottling. This one was another big surprise for me. The rebottled vermouth had two things going for it: less headspace and the fact that I didn't open them over and over. And yet, more people correctly identified the rebottled sample—and disliked it—than the sample purged with inert gas.

Of course, I recognize that my experiment wasn't perfect. I did my best to randomize the order of samples and prevent tasters from guessing which was which, but I couldn't do much to prevent fatigue in the tasters. Ever tried sipping twelve samples of nearly identical liquids in quick succession? Is it any surprise things started to taste the same? On top of that, we only had access to plastic cups and I didn't go through the process of training any of the participants prior to tasting (a step that most sensory scientists would have taken, had this been experiment been designed for peer-review).

That said, I do think these imperfect results shed a little light on what does and doesn't matter when it comes to storing vermouth.

So, how should you store vermouth? It normally takes me about one to two months to go through a bottle of full-sized bottle of sweet vermouth. Based on these experiments, I'll be storing my vermouth in the fridge without inert gas or at room temp with inert gas if I don't have fridge space.

If I had to store vermouth for longer than a month or two, I would purge the vermouth with inert gas and leave it in the fridge if possible. I still think rebottling into smaller bottles is a good idea as well, but based on the experiments, I now think you would get the best results if you intentionally left a little headspace in the smaller bottles and purged it with inert gas, rather than rebottling into small bottles without the purging step.

Notes:

1. Jackson, Wine Science Principles and Applications (2008), pg. 503; originally Roussis et al., Inhibition of the decline of volatile esters and terpenols during oxidative storage of Muscat-white and Xinomavro-red wine by caffeic acid and N-acetyl-cysteine (2005).

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