Influence of intrinsic factors on conventional wine protein stability tests

The influence of intrinsic factors on the results of ethanol, tannin and heat tests, routinely used to assess wine protein stability, was studied. Experiments were performed on 23 Portuguese and Austrian wines. The factors considered were total protein content, pH, ethanol content and the amount of several relevant cations (calcium, iron, copper, sodium and potassium). The protein profiles were analysed by HPLC fractionation. The heat test was a good indicator of total protein content while the ethanol and the tannin tests showed significant interference by the other factors. A factorial design at two levels in selected samples was also performed to assess the influence of pH, storage temperature, tannin concentration and ethanol concentration on the development of turbidity. Results indicated that ethanol content had no significant influence, and that pH and storage temperature had a significant influence, though only when tannin was added.