|Image: Paige Green for Ten Speed Press/True Brews|
The chlorine in tap water can make life difficult for yeast and can interfere with fermentation. Most sodas are made with a large percentage of fruit juice, so the chlorine in the added tap water is rarely an issue. The ginger ale and the orange cream soda aren't so lucky — since they're made with mostly water, chlorine can become an annoyance. (If you've made either of these sodas and didn't have a problem, that's likely because your tap water is low in chlorine. This is the case with my own tap water and why I didn't catch the problem in testing — my sincere apologies on that!)
The solution is to use filtered water in these brews or dechlorinate your water before beginning (see page 14 in True Brews for info on dechlorinating water).
Thanks to everyone who emailed me about this and brought the issue to my attention! I'll be adding a note about using filtered or dechlorinated water for these two recipes in the next printing of True Brews. Happy brewing!