The relationship between total acidity, titratable acidity and pH in wine By: Roger Boulton In: American Journa l of Enology and Viticulture. 31(1): 76-80. 1980 • This is an older paper, but worth revisiting given the impact of a wine’s acid composition a pH on so many parameters, which Dr. Boulton summarizes like this: - sourness, as well as organoleptic properties - microbial stability - incidence and extent of malolactic fermentation - solubility of potassium bitartrate and calcium tartrate - rates of formation and hydrolysis of esters - ionization and rate of polymerization of anthocyanins - protein instability in white wines. • Dr. Boulton starts out by defining the terms involved. Total acidity: proton equivalence of the amount of organic acid anions present in a wine. It is the number of protons (also called hydrogen ions, or simply H+) that the organic acids (lactic, succinic, citric, acetic, and sulfurous acids) would contain if they were undissociated. It is calculated by measuring the acid anion concentration (by spectrometry or chromatography), expressing them as molar quantities (number of molecules per volume), and then multiplying by the number of protons that would result from complete dissociation. Titratable acidity: number of protons recovered during a titration with a strong base to a specified endpoint. It can also be expressed as a molar quantity. Many people use titratable acidity and total acidity as synonyms, but they are not. The titratable acidity is always less than the total acidity, because not all of the hydrogen ions expected from the acids are found during the determination of titratable acidity. However, titratable acidity is easier to measure. pH: logarithm of the concentration of free protons, expressed with a positive sign. • This study proposes that the reason why not all (only some) of the hydrogen ions from the organic acids are detected by titration during titratable acidity determination is the exchange of...
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