For those of our fellow grape nuts who don’t know, bulk aging refers to aging wines in vessels other than the final bottle whereas bottle aging refers to wines aged in their . . . um, you got it — bottle. Your question is a good one, though, and one that isn’t often addressed in a lot of home winemaking books and Websites.
To answer the easy one first: If your full-bodied red kit wine is dry, stable, sound and is pretty tannic and colorful (i.e. has lots of natural antioxidants) I’d say that a year in a 6-gallon (23-L) carboy before bottling is just about right. Just make sure that the container is completely full and is well sealed as oxygen can damage finished wine during the bulk aging stage. I wouldn’t leave it in for much longer than that, though, and would think about getting your bottling equipment sanitized and ready.
And now for the compare and contrast of bottle aging vs. bulk aging part: It’s safe to say that every wine that ends up in a bottle goes through both stages, at least nominally. Bulk aging can be as simple as letting your wine “settle down” in its carboy for a couple of weeks after primary fermentation is done with and bottle aging can be as short as the three weeks that elapse between putting the cork in and screwing the cork out. It really is up to you — which perhaps is the most critical point of all — each wine (and wine drinker) is different and there are no hard and fast rules that dictate how much of each type of aging a wine will need. It all depends on your wine and your tastes.
Just so I’m not leaving you hanging like a neglected cluster of late-harvest Riesling, here’s a little bit more information to chew on. The general purpose of bulk aging is to let the wine do what I call “finding itself” post-fermentation, which entails, physiologically and chemically, a couple of important things. First of all, a wine needs to 100% complete its primary fermentation. Any wine that is still going through these initial fermentation stages, in my opinion, is not finished wine and will lead to fizziness and cloudiness in the bottle (if bottled too early). A wine also must lose the carbon dioxide it might have retained from its fermentations and it has to have enough time to settle out its natural sediments (“lees”). If you’re so inclined, you could go through other steps like filtration or cold stabilization, but these are just icing on the cake. After a wine is inactive and settled out, the main determinant of when to bottle should be taste. Gutsy red wines like yours may need 12 months in the barrel or carboy to mellow out their harsh tannins whereas some delicate, white wines can technically be bottled as soon as they fall bright. It’s never a good idea to bottle too early but also do err on the side of caution. Bulk aged wine, if not cared for, can be at risk for oxidation or spoilage.