Unlike wine, brandy ceases to mature once it is in glass. Brandy can slowly go downhill in the bottle but this takes many many years, possibly a lifetime. Some experts say that while cognac doesn't improve in the bottle, it does "settle." Since Cognac is blended, the longer the elements are together the more completely they integrate.
Also dissimilar to wine, brandy must be stored upright. Spirits can wreak havoc on cork, and given enough time can actually rot it away. Once brandy is opened, the fresh air has an oxidizing effect. (With a young brandy this can be a good thing). When storing liquor at home keep your bottles in a cool dark place, not over 70 degrees Fahrenheit and not under 50.
