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2024-09-13 14:21本頁(yè)面
【正文】 orms Mechanics of Wine Buffer Chemistry ? Simple buffer equilibrium (weak acid buffer) HA ? H+ + A ? Upon addition of acid, free H+ consumed by A: A + H+ ? HA ? Upon addition of base, OH reacts with H+ to produce water: OH + H+ ? H2O ? Limited change in pH will occur, due to these interactions ? In each case, the original equilibrium will be reestablished at the new pH based on Ka values Wine Acidity Titration Curve ? Weak acid vs. Strong Base, therefore endpoint is pH 7 ? Flat areas of curve show areas of greatest buffer capacity ? Although wine is a mixture of weak acids, it is not possible to separate them by titration as the pKa values are too similar ? Therefore we only see the one inflection point Effect of Potassium Ions on Wine Acidity ? Titratable acidity values will vary with potassium ion content ? Potassium is a significant ponent of grape juice ? Potassium ions modify the dissociation equilibrium of anic acids ? This is due to binding of anic acid ions (particularly bitartrate) as the potassium salt ? Some potassium acid salts react with NaOH during titration, others do not. Effect of Alcohol on Wine pH and acidity ? Equilibrium chemistry of wine acids and salts is modified by presence of alcohol ? Solubility of some species is lower in alcoholic solution, particularly tartrate salts ? Wine has a lesser buffer capacity than juice Consequences for Winemaking ? Difficult to significantly alter high pH levels in jui
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