I use litmus paper. Be aware though that it comes in a variety of ranges. The stuff you find at the pool supply places probably won't have the range you seek. Try a lab supply place. You might also be aware that pH doesn't give you concentration, only relative strength. Something might have a pH of 1 and still be harmless. Both Ralphs' and my Red Savina mash (CaJohns' Krakatoa) register between 3.0 & 3.5. Shelf stability is also dependant upon a great many other things, such as bottling temperature, aseptic techniques, and other such things. There are several others on the list who are quite knowledgable about this stuff. Right Cameron? -Jim The Elder C Mild to Wild Pepper & Herb Co. http://www.wildpepper.com