Originally Posted by cyberbackpacker
When you start to (fly) sparge, your sugar/water ratio starts to drastically change, and your pH level begins to increase. That is why it is essential to monitor pH and/or gravity when fly sparging so you do not extract tannins.
I am wondering about something:
Since tannins are tannic acid, it seems to me that if your pH starts out low and then rises during your sparge, that you have already extracted all the acid/tannins. A pH of 7.0 is neutral and anything below that is acidic. If pH is low and then rises, you have gone from acidic to neutral to basic.