I'm working with a recipe for a black ale (Cascadian Dark Ale) and it's telling me to dry hop 0.25 oz Warrior hops and 0.5 oz Cascade hops right after transferring to the carboy. I had read that the best time to dry hop was after some of the fermentation had already taken place. Is this timing special to the Cascadian dark? What are the consequences of dry hopping this early in the fermentation? Should I adjust the recipe?
There is nothing special about the style. The best time to dry hop is … immediately before serving, ultimately. Hops fade as a function of time, so minimizing the time between introduction and consumption is key. E.g., if you want to age/condition your beer for 3 weeks post-primary before serving, and want to dry hop for one week, you should introduce the dry hops after 2 weeks.
The instruction to add hops to the carboy is a little unusual, but if you think about it, its kind of like a post-chilling whirlpool addition, so its not totally unheard of. You will loose some delicate aroma through off-gassing during fermentation, and since its only .75oz total, I doubt this addition will contribute much to the finished beer.
Some folks advocate adding dry hops at the tail end of fermentation, but before its totally done. The idea being that the last bits of C02 from the fermentation will help drive out the oxygen introduced with the dry hops. I suppose this is more important with loose leaf hops as opposed to vacuum-sealed pellets. You will loose a touch of dry hop character from adding them early like this, but the trade off is that less oxygen post-fermentation means that the beer tastes better for longer.
Aroma = molecules in the air detected by olfactory neurons in your nose, so it makes sense that if your yeast are producing lots of CO2, the gas will carry away some of your nice aroma molecules and reduce the effectiveness of the dry hop, which is really about maximizing that hop aroma. In my experience, 2-4 days before bottling/kegging seems to work well, a week max. The last IPA recipe I did recommended fermenting a week then dry hopping for 2 weeks so I tried it. It still has a big hop aroma, but I think it resulted in a bit less hop aroma than the 2-4 day dry hop I've done before.