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What it does :
Tests with pH paper are used to test the mash to ensure that the pH is appropriate for the type of grain conversion being attempted.
What it is:
Litmus paper, or pH paper, is a special test paper that, after contact with a liquid, changes color to indicate the degree of acidity or alkalinity.
How it works:
The paper is treated with a water-soluble mixture of different dyes. The dyes change colors under different levels of acidity or alkalinity. Blue pH paper turns red under acidic conditions and red pH paper turns blue under basic, alkaline conditions.
Use of pH papers occurs during the hot side of brewing (e.g. wort preparation). However, they do not come into contact with the wort, and are disposable. So, simply keep them dry before use.