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The Significance of pH during Wine Production and Ageing

• The acidity of grape juice and wine, measured as pH, affects many aspects of wine production and ageing.
  
  These include the many chemical and biochemical reactions involved in the production and ageing of wine.
  
  
• A low pH, ensures that more of the anti-oxidant/anti-microbial agent, sulphur dioxide (SO₂), will exist in the more effective molecular form.
  
  
• A low pH, inhibits the growth of bacteria and to a lesser extend yeasts.
  
  
• A low pH, also selects in the favour of the desired, cleaner fermenting Lactic Acid Bacteria (LAB) to conduct a malolactic fermentation (MLF).
  
  
• A low pH, favours the increase in desirable flavour compound production and a decrease in undesirable compounds formed during fermentations.
  
  This applies to both yeast and malolactic fermentations (MLF).
  
  
• A low pH, shifts the equilibrium towards the more desired, coloured form of red pigments.
  
  Red pigments, extracted from red grape skins during fermentation, can exist in the colourless, blue and red forms.
  These pigment forms exist in equilibrium with each other and the [H⁺] (hydrogen ion concentration).
  The lower the pH, the more the equilibrium will shift from the colourless to the red form.
  
  
• A low pH, slows down the ageing process of wines, allowing wines with aging potential to develop those sought after aged flavours that develop with time.
  
  That is, just as a cool, dark and undisturbed wine cellar of constant temperature is ideal for the desirable slow aging of wine, a low pH will aid this process.
  
  
• The reduction of pH, through acid additions at the earliest opportunity, in anticipation of the decrease in pH during wine production, is highly recommended.
  
  Note however that so many novice wine makers, armed with a modicum of knowledge and little experience, end up making wine with a perfect set of numbers, an ideal pH and great keeping qualities, but alas a permanently unbalanced, undrinkable wine.
  
  
• pH does affect the taste of wine, with pH values around 4.0 resulting in flat tasting wines and with wines below 3.0 becoming excessively tart tasting.