Potasium Carbonate is used by distillers to buffer the mash against pH changes and to prevent it from going too low. The ideal pH for mashes being prepared for distilling is between 4 and 4.5. The higher the pH the lower congeners (within limits).
Potassium Carbonate powder is highly hygroscopic (attracts water from the atmosphere) and should be stored in an airtight container. However if it is left to absorb water from the atmosphere it will turn into a watery liquid (hydrated potassium carbonate) that could also be used without any ill effects to buffer/lower the ph of a mash.
- It is a much better buffering agent than for example calcium carbonate as it readily dissolves in water and contributes to the nutrients for yeast growth.