A buffer or buffer solution, as related to pH, is typically a solution consisting of a weak acid and its conjugate base, or a weak base and its conjugate acid. The purpose of the buffer is to decrease the impact to pH when a differing acid or base is introduced to the solution.
PH plays an important role when it comes to a brewer’s mash. You will find brewing pH stabilizers available on the market, such as pH Stabilizer 5.2, which is a sodium phosphate salt-based buffer; please be aware that there is a great deal of disagreement about how beneficial or detrimental they actually are. Ideally, you would control the mash pH of each individual beer style by comparing your home water profile to that of the desired water profile of the beer you are brewing, and make the appropriate water adjustments that way.
Additionally, some of the popular home brewing software on the market will also help you determine the proper water additives based on the estimated pH level of the grain bill that you are brewing with. Lastly, there are a variety of pH measuring strips and meters available on the market, which can help you determine if adjustments need to be made to your mash.