Influencing grape and wine pH

Similarly, too much uptake of these nutrients, as a result of good water availability, will also spoil wine quality through increasing pH. The pH of the juice/must affects the taste, sugar/acid balance and stability of wines. It is determined by the balance of the major anions (malate and tartrate) and presence or absence of major cations (mainly potassium). Harvest timing and management also effects wine pH. The pH can increase by as much as 0.2 units between harvest and delivery. 

High pH values can alter the color of anthocyanin solutions – responsible for red wine color - by changing the structure of the anthocyanin molecule. A high pH must, results in wines that have a flat taste and red wines with a brownish color. Generally, a pH above 3.6 is undesirable as it can have a negative effect on a range of wine quality characteristics.

Crop Nutrition and Grape and Wine pH

Nitrogen

High nitrogen increases the pH of the must and wine, increasing the malate concentration in grape juice. Too much available nitrogen on the other hand can create strong canopy growth, increasing shading and wine pH.

Potassium

There is a strong relationship between potassium and grape and wine pH. Too much potassium results in a high wine pH and a poorer quality wine.