After you rack off the gross lees, you can add oak.
How much to add is a difficult question. How much wine do you have and how much oak flavoring do you want?
I add 1.5 to 2 oz cubes to 5 US gallons / 19 liters of red wine. For blackberry, I'd add half that, maybe less, as the wine is lighter in body and flavor. If you add 1/2 oz per 5 gallons, let it rest 6 to 8 weeks, then gently stir to homogenize, and taste. If you want more oak character, add more oak and repeat.
I'm ready to start a new 5 gal. kit of Cabernet Sauvignon. I want to add some chocolate nibs and oak chips, maybe a little vanilla.
Any suggestions on how much of each to add and when to add?
Thanks for the help!
Oak is easy -- both before and after fermentation. 2 oz added before fermentation is "sacrificial tannin", which will preserve natural grape tannin. Another 2 oz during bulk aging will impart oak character.
Chocolate and vanilla? Others will have to chime in on those.
Regarding oak and aging, read the tasting notes from my oak stix experiment. The ways the tastes of the 4 wines changed during the course of the experiment was frankly surprising.
Tonight my son and I bottled the 4 carboys. After bench testing, we blended the 3 stix carboys as the combined oak flavors were superior to the individuals.
Per usual, we poured glasses for quality control purposes during the initial rackings. Half glasses of wine sat out for several hours, and when tasted again, the breathing improved all the wines. This is not a surprise.