I feel like, if this is intended behavior, it should be in the guides somewhere. It's really unintuitive to have alcohol spoil (when in the base game it doesn't) and not use barrels for long-term storage or proper aging (when in real-life those are things they are used for).
Is there currently a way to age brandy into aged-brandy? Again, the barrel wouldn't let me seal it (even before it was spoiling), the guides don't say, and bottled brandy did not have a maturation counter on it in any way. It says "curable" but there's no instruction as to how to "cure" it in the guides. Do I just put it on a shelf? Does it need a special room? It still says it'll spoil even in the bottle, so I don't know what that's about?