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 degrees F will be .35 less than at 65 degrees F. For example if a 150-degree mash had a pH of 5.4 then a reading at 65 degrees 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.

If the pH of the mash is too low (too acidic) the addition of calcium carbonate will work well to raise it. In some cases, especially if you are making a very dark beer, you may have to settle for a mash pH as low as 5.0 but under no circumstance should you add more than 2 teaspoons of calcium carbonate to a five-gallon mash. If the pH of the mash is too high (too basic/alkaline) the addition of calcium in the form of calcium sulfate (gypsum) or calcium chloride is the most acceptable way to lower it. In either event starting with ½ teaspoon additions at a time is recommended. Mix well and recheck the pH after each addition. If this is not available or if you would like to brew with very soft water, then the addition of phosphoric acid can accomplish acidification of the mash. Teaspoon additions can be added incrementally until the desired pH is achieved.

There is, also, a technique called an "acid rest" which can be employed to lower the pH of the mash by varying degrees. The enzymes responsible for this are most active at a resting temperature of 95 degrees F for 15 minutes to a half an hour.