Do you need to add alcohol to a mixing bottle?

Alcohol helps stop the water from going off. Many people add some brandy or other strong spirit to a mixed bottle, especially if the bottle will not be kept cool – if, say, they intend to carry it about in their pocket all the time. A teaspoon of brandy – about 5mls – is usually enough.

Other ‘non-alcoholic’ ways of keeping the contents fresh include keeping the bottle in a fridge, or adding a teaspoon of cider vinegar or vegetable glycerine.