winephacidity-wenkub
2022-09-12 14:21:30 本頁面
【正文】 e concentration of the H+ ion in solution ? pH = log[H+] ? pH in fruit juices ranges from around 2 in lemon juice to around 4 for warm climate grapes ? Hydrogen ions are produced by the dissociation of acids in solution (under equilibrium) ? HA ? H+ + A pH versus Titratable Acidity ? pH is a measure of [H+] only ? pH in wine depends on both the concentration of acids present and their relative degrees of dissociation ? Titratable acidity measures free [H+] plus all undissociated acids that can be neutralised by a base ? pH and TA are not the same thing, nor do they have a linear relationship! Organic acids in wine ? Diprotic acids: ? Tartaric acid ? Malic acid ? Succinic acid ? Triprotic acids: ? Citric acid ? Monoprotic acids: ? Acetic acid ? Lactic acid ? Acetic, Lactic and Succinic acids are products of fermentation Weak Acid Dissociation in Wine ? The degree of dissociation is specific to each acid ? denoted by the dissociation constant (Ka) Ka = [A][H+] [HA] ? Diprotic and triprotic acids have a K value for each hydrogen ion (K1, K2 etc) ? In wine, K values are typically around 105 ? This represents only about 1% dissociation ? Tartaric acid is the ‘strongest’ acid – 50% dissociation of first H+ at pH Dissociation Constants of Organic Acids in Wine Acid KA pK in Wine (12% Alc, 20 deg) Tartaric (1) x 104 (2) x 105 Malic (1) x 104 (2) x 106 Citric (1) x 104 (2) x 105 (3) x 107 Acetic x 105
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