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【正文】 1991 ? Delfini amp。 Acidity Concepts and chemistry of pH, anic acids, buffer capacity and wine quality implications of pH Downloaded from Effects of pH on wine ? biological stability – spoilage anisms are generally inhibited at lower pH, whereas high pH may favour them ? colour particularly of reds, lower pH wines exhibit more purple and ruby tones, higher pH wines more brick and orange tones ? oxidation rate – increased at higher pH ? protein stability – lower pH tends to foster more rapid precipitation of unstable proteins Effects of pH on wine (cont) ? effectiveness of preservatives – the active (molecular) forms of sulphites and sorbic acid exist at higher levels at lower pH ? tartrate stability – dissociation of tartaric acid is pH dependent ? Overall palatability is affected by wine pH Definition of pH ? pH is related to the 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 acid
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