How Long Does Vermouth Last Once Opened?

About a month in the fridge. That is the short answer, and the reason it surprises people is the second thing worth knowing: vermouth is wine, not spirits, and it behaves like wine.

Why it goes off

Vermouth is wine that has been fortified with a neutral spirit and infused with herbs, roots and spices. The fortification takes it to somewhere between 16 and 18% ABV, which is a long way short of the roughly 40% that keeps a bottle of gin stable indefinitely.

At that strength oxidation is the enemy, and it starts the moment the cork comes out. The fresh, bright herbal notes go first, then the fruit flattens, and what is left tastes stewed and vaguely of raisins. It is never dangerous. It is just dull, and it makes the drink dull with it.

The timeline

• Unopened, anywhere cool and dark: a year or more, and most bottles carry a best-before date that is honest.
• Opened, in the fridge, capped: at its best for about a month. Drinkable for two or three.
• Opened, on a warm shelf: noticeably worse within a week, and past saving inside a month.

This is the single most common reason a home-made Manhattan tastes flat when the recipe was followed exactly. In that drink the vermouth is a third of the glass. There is no citrus and no soda to hide behind, so a tired bottle is exactly as obvious as it sounds.

How to tell

Pour 15 ml and taste it on its own, cold. Good vermouth is pleasant to drink neat: aromatic, a little bitter, sweet or dry depending on the style. Vermouth that has gone tastes thin at the front and sharp at the back, like a wine that has been open too long, because that is what it is.

Do this before you build the drink rather than after. A Manhattan is 60 ml of whiskey and it is worth checking the cheaper ingredient first.

What to do about it

Buy the small bottle

Most recipes use 15 to 30 ml. A 375 ml bottle you finish inside a month is better value than a litre you throw away, even at a worse price per millilitre. This is the fix that solves the problem rather than managing it.

Refrigerate it, always

Both sweet and dry vermouth belong in the fridge after opening. The cold roughly halves the rate of oxidation and it means the vermouth is at the right temperature when you build a stirred drink.

Drink it as a drink

The easiest way to finish a bottle is to stop treating it as an ingredient. Dry vermouth over ice with a twist of lemon is a genuinely good aperitif at about 18% ABV, and sweet vermouth with soda and an orange slice is most of an Americano before you have added anything. Both belong in the low-ABV category for the same reason.

Use it faster

If you have an open bottle of each, the drinks that will get through them are the Dry Martini, the Negroni and the Manhattan. That is one bottle of gin, one of whiskey and a bottle of Campari between them, which is a short shelf that covers a lot of ground.

What not to bother with

Vacuum stoppers and inert-gas sprays help a little and cost more than the bottle. Freezing works and dulls the aromatics. The honest answer is a smaller bottle in a colder place, used sooner.