When exposed to direct sunlight, whiskey can evaporate and lose its alcohol content, so store it in a secure container inside a dark place at around 55 to 60 degrees Fahrenheit.
This slows down the natural aging process and protects the color and proof during long periods. A cellar is perfect for storage, but a fridge will suffice in the right conditions.
Transferring the remaining spirit into a smaller, closed container, like a decanter, minimizes any empty room and decreases the chances of further degradation.