As an expert sommelier and brewer, I can confidently say that vermouth does go bad, just like any other alcoholic beverage. However, the shelf life of vermouth can be extended if it is stored properly.
Vermouth is a fortified wine that is infused with various botanicals, herbs, and spices. These ingredients give vermouth its unique flavor and aroma. However, these ingredients also contribute to the degradation of the vermouth over time.
Once you open a bottle of vermouth, it is crucial to store it in the refrigerator. The cold temperature helps slow down the oxidation process and preserves the flavor and freshness of the vermouth. Leaving it at room temperature will accelerate the deterioration of the wine.
In terms of the shelf life of vermouth, an opened bottle will generally stay in good shape for about a month when stored in the refrigerator. During this time, the vermouth will maintain its flavors and aromas, allowing you to enjoy it to the fullest.
However, after the first month, the quality of the vermouth will start to decline. The flavors may become less vibrant, and the aromas may fade away. While it may still be drinkable, it won't be as enjoyable as when it was freshly opened.
If you find yourself unable to finish the bottle within three months, it's best to consider sharing it with friends or family or even giving it away. Vermouth is often used as an ingredient in cocktails, so hosting a gathering or mixing up some drinks can be a great way to utilize the remaining vermouth.
To summarize, vermouth does go bad over time, especially once it is opened. Storing it in the refrigerator can help prolong its shelf life, with the vermouth staying in good shape for about a month and remaining passable for up to two months. If you find yourself with an excess amount that you can't use within three months, it's best to share the vermouth with others to prevent it from going to waste.