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pH Buffers

by Bill Reeder


One of the least understood parts of brewing is making water adjustments.  Homebrewers can make beer that tastes great just by using tap water, however when a person wants to take brewing to the next level, water adjustments is the place to begin.  Mash pH is critical in getting the best possible efficiency out of brewing grains.  In order to convert the stored starches in grains into fermentable sugars, enzymes must begin breaking the starches apart.  In order to do this the enzymes need to be at the right temperature and the correct pH.

Many brewers decide to use acids and bases in order to get their mash pH to the correct level (right around 5.2).  The easiest way to do this, for the non chemistry minded individual, is to use a pH buffer that will hold the pH right where the brewer wants it.  This is where Five Star’s pH stabilizer comes in.

Equilibrium is where the pH of a solution becomes constant.  If a person adds more acid or base, the mixture will reach equilibrium again (where the hydrogen ions are in a constant back and forth battle that ends in a constant pH).  If a person wants to, by using a buffer, he or she can lock this equilibrium into a specific pH.  pH is essentially a measure of how many free hydrogen ions are in a solution. 

Buffers act by utilizing conjugate pairs.  If we think in every day terms and look at HCl or hydrochloric acid, we can imagine throwing the acid into water and the first thing that happens is that the hydrogen ion will leave the chloride ion.  This will result in an H+ ion and a Cl- ion.  HCl is an acid, however the resulting Cl- is now a base (called the conjugate base), meaning it is now a hydrogen ion acceptor, as oppose to the HCl being a hydrogen ion donor. 

The basis behind a buffer is that if a person adds an equal amount of acid (HCl) and conjugate base (Cl-) then a person creates a buffer.  If a new hydrogen ion is introduced, equilibrium will continue as the hydrogen ion binds to the Cl-.  This is best seen in weaker acids such as Phosphoric acid (as in Five Star’s pH stabilizer).

While HCl is a mono-protic acid (as in only one H+ to donate), Phosphoric acid is a     tri-protic acid (H3PO4, see picture), where it has three hydrogen ions to potentially donate.  Once one hydrogen ion is lost from Phosphoric acid, the resulting conjugate base (H2PO4-) can now be an acid (as it still has a possible two hydrogen ions to donate) or it can act as a base (it wouldn’t mind getting it’s lost hydrogen ion back).  Again, if this resulting conjugate base acts as an acid and gets rid of another hydrogen ion, it’s resulting conjugate base (HPO42-) can again lose another hydrogen ion (although not likely to lose it’s third) or it can accept its lost hydrogen ion as a base would do. 

The end result is that by adding varying amounts of acids and the resulting conjugate bases, a person can create a buffer solution that will lock in a specific pH.  If a new hydrogen ion is added to the solution, on of the conjugate bases will bind to it and in sense neutralize it, maintaining the appropriate pH.  If a base is added, such as a hydroxide ion (OH-) then a hydrogen ion will be released from one of the acids in order to neutralize the hydroxide ion, all the while maintaining the pH where needed.

This all seems pretty in depth, although this isn’t even the tip of the iceberg when it comes to acid-base reactions and pH, the fact is that by adding one tablespoon of pH stabilizer will lock the mash pH to 5.2 which is where the amylase enzymes are the happiest.  If adding a tablespoon of a something sounds too easy, by all means, grab a pH meter and some acids and bases and see how it works. 

This article was published on Thursday May 27, 2010.
Products related to this article:
5.2 pH Stabilizer-l lb
5.2 pH Stabilizer-l lb