The best way to ensure that your whisky won’t go soft on you is to leave as little oxygen in the bottle as possible.
STORE YOUR WHISKY UPRIGHT
Alongside light exposure, the position of whisky bottles is important to consider. Unlike wine bottles (which are recommended to be stored horizontally), whisky should be stored upright. Where wine corks are made to stay in contact with the spirit to keep it moist, they are not made for repeated use once opened. In contrast, whisky corks are designed for extended use once opened, but should not be consistently wet or they will cease to be effective. This is because the high alcohol content in the spirit will start to degrade the cork over time.
WET YOUR WHISKY CORK PERIODICALLY
While it may seem to directly contradict the tip above, a perfectly dry cork will become brittle over time, which can be just as damaging for your whisky in the long run. A brittle cork will lose its seal, and can even break off into the bottle. With this in mind, every so often it is beneficial to tip your bottle over to briefly wet the cork and keep it moistened.
There is also an odorless gas you can spray inside the whisky bottle. It is called argon gas. Argon gas is heavier than oxygen so it will be between your whisky and the oxygen. Like an odorless and see threw layer of protection.
Your closed bottles can be preserved by wrapping the cork and neck of the bottle with parafilm. This prevents the liquid from evaporating through the cork.