winephacidity-文庫吧資料
2024-09-09 14:21本頁面
【正文】 sures 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 Succinic (1) x 105 (2) x 106 Lactic x 104 Example: Distribution of tartaric acid species at various pH Wine is a Chemical Buffer System! ? A buffer solution resists changes to pH when addition of acid or base is made ? Buffer solutions consist of a weak acid and its conjugate base (or vice versa) in chemical equilibrium ? The buffer capacity of wine is a result of the bined effects of different anic acids in both their dissociated and salt f
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