Yeah, I'm brewing kombucha too. Somewhere I saw a kombucha enthusiast make a great recommendation: Double-brew for extra bubbles! I tried this technique with my most recent batch, and sure enough they're bubblier than ever. Almost scary, they're so effervescent, and in fact I've heard the bottles can explode, so I'm excercising caution while I'm new at it. The trick is to put a couple of raisins (and I added goji berries too) in a finished bottle and keep it out on the counter while it integrates the additional dried fruit (for days or weeks). Then it's ready to pop like champagne! Are you familiar with this technique?