"The pH scale describes how acidic or basic (alkaline) a solution is. The scale ranges from 0-14: 7.0 is neutral; less than 7.0 is acidic, becoming more so as it heads toward 0.0; greater than 7.0 is alkaline, becoming more so as it heads toward 14.0.Its measurement is affected by temperature. The pH of a solution at 150 °F will be .35 less than at 65 °F. For example if a 150-degree mash had a pH of 5.4 then a reading at 65 °F would indicate a pH of 5.75.
The enzymes in the mash responsible for converting starch to sugar work optimally at a pH of 5.2-5.6. Thus it is of the utmost importance to the all-grain brewer that he/she is cognizant of his/her mash pH if optimal efficiency is to be achieved. Likewise hop utilization is also affected by pH level. The best wort pH for optimum hop utilization is between 5.0-5.4.A measure of pH of the brewing water will not give a measure of what the mash pH will be. The mineral content, particularly calcium, is more influential than the apparent pH of the brewing water.
Your pH can be approximately measured using ""pH papers"" or ""pH meters."" Remember that pH papers are accurate only at room temperature so hot water samples must be cooled before the reading is taken. Also many pH meters work this way as well especially the more inexpensive ones."