What is the difference between pH and titratable acidity (TA) in wine?
- pH: the amount of free hydrogen ions (protons) in a solution
- TA: all disassociated protons of a solution; titratable acidity is not total acidity
Why should a winemaker care about acidity?
When it comes to acidity, Clark emphasized that titratable acidity (TA) is directly related to what people taste, in terms of sourness, on the palate.
When an individual takes a sip of wine, the mouth produces saliva continuously until all the acid is neutralized. Humans perceive this as "sourness," "tartness," or "acidity." The more disassociated protons in solution, therefore, the more sour a wine/beverage/food item will appear.
According to Smith, a titration is analogous to an "analytical mouth." In the laboratory, the acid in solution (typically held in a beaker) is being neutralized, chemically, by the base that is being titrated (held in the burette). This procedure is visualized by a color indicator, which indicates the "end point" in the titration. When all of the acid is neutralized, the solution in the beaker will change a color.
pH, on the other hand, is not directly related to the sourness intensity that is tasted. Theoretically, two wines can exist at the same pH, but have two different TA concentrations. The wine with the higher TA will actually taste more sour than the wine with the lower TA.
However, pH is important as it manages all of chemistry and microbiology decisions in the winemaking process. Therefore, all chemical reactions and microbiological stability in the wine is related to pH. This includes things like:
- Color stability of red and rosé wines
- Tartaric acid [cold] stability
- Microbiological stability, growth, and survival
- Sulfur dioxide concentrations
Clark emphasized that many winemaking decisions cannot be made without making a reference to the wine's pH. In order to make decisions during the winemaking process, knowing the pH of that wine can often help direct which direction a winemaker should choose.
An example of how pH influences winemaking decisions includes the addition of sulfur dioxide to wine. At a lower pH, a winemaker does not need to make high potassium metabisulfite additions in order to obtain an adequate molecule concentration of free sulfur dioxide. At higher pH's, a winemaker may need to make very high potassium metabisulfite additions to obtain adequate antimicrobial protection of the wine.