Good quality leather boots are a style investment that will last for years if you take care of them. This can backfire if you leave them in storage, only to retrieve them years later, ripe with the musty odour of mould or mildew. While this can easily be prevented--see Tips--once the mildew smell has set in, you must treat the boots for the mildew or mould that’s causing the odour before you can get rid of the smell.
Bring the boots out of storage and place them in a dry, well-ventilated area, out of direct sunlight that might fade the leather. This gives any damp areas that might be mould breeding grounds a chance to dry out.
Mix one part rubbing alcohol and one part lukewarm water in a small bowl. Moisten a cloth in this mixture and wipe down the outside of the boots. This should kill any mould or mildew that is causing the musty odour.
Wipe the boots down with a clean, damp cloth to remove any traces of alcohol, then pat dry with a dry cloth.
Spray the inside of each boot with a light mist of any shoe freshener spray and leave in a well-ventilated place to dry. Examples of possible shoe sprays include Tana Fresh Force (see Resources) and peppermint oil spray, which is widely available at boot shops under a variety of brand names.
Place a clean, dry paper bag inside each of your leather boots. Fill each bag with charcoal briquettes, place the both boots inside a large paper bag (or each boot in a medium paper bag, if no large bags are available) and roll the top shut. Leave overnight; the boots should smell fresh when you retrieve them in the morning and remove the charcoal.
You can store your boots with charcoal inside them--in a paper bag, of course--to help prevent the return of mould or mildew odour.