How long does rum keep after opening?

Drinks with an alcohol content of 10% or more are among the foods for which a best-before date is not mandatory.

The Netherlands Food and Consumer Product Safety Authority lists these drinks among the exceptions, alongside wine, fresh fruit and vegetables, vinegar, salt and sugar, among others. With at least 37.5% alcohol, rum is well above that threshold. So the absence of a date does not mean it has been forgotten, but that the regulations do not require one.

From an open or half-full bottle, ethanol and some of the aroma and flavour compounds escape through evaporation.

That is what the entry on oxidation in the Oxford Companion to Spirits & Cocktails, written by Doug Frost, says. It does not make the drink unsafe; the lightest aroma and flavour compounds are simply the first to go. With a bottle you finish within a few months, you will rarely notice. With a bottle that stands half full in the cupboard for years, you will.

Yes, because in an almost empty bottle a large layer of air sits above a small amount of rum, and that speeds up the change.

What counts is the ratio of air to liquid, not the time since opening. If you want to keep the last bit, pour it into a smaller bottle that you fill almost to the top. A ten or twenty centilitre bottle with a good closure works well for this.

Stand the bottle upright in a dark place at room temperature and screw the closure firmly shut after every pour.

Upright means the rum is not constantly in contact with the cork or cap. Dark and at an even temperature means light and heat do not speed up the change. The fridge is not necessary. An ordinary cupboard, out of the sun and not next to the cooker, is enough.

No, because such bottles contain more sugar and often less alcohol, which makes them more sensitive than pure rum.

Regulation (EU) 2019/787 stipulates that rum is not flavoured and may contain at most 20 grams of sweetening per litre. A flavoured or heavily sweetened bottle therefore falls into a different category, with its own requirements for alcohol and sugar. If such a bottle does carry a best-before date, follow it.