A: You can use both! We recommend keeping anywhere between 1-3 cultures in your brew at a time. Eventually you will want to discard old cultures and use the newest ones. Old cultures are ready to be retired after 10-15 brews, or if it turns a really dark brown and can be ripped apart easily. Oftentimes, your old and new culture will form into one large culture which is great as well. If your cultures continue to grow onto each other, be sure to keep the whole culture under 2 inches thick (height). Simply peel off the oldest layer to accomplish this, or cut in half. It's important not let it get too big (over 2 inches thick) as it will start to inhibit the flow of oxygen to your brew, and process the sugar too quickly, which will throw off the proper yeast/bacteria ratio.