The effects of different protein:tannin ratios on the tartrate-holding capacity of wine model solutions

- We study the potassium hydrogen tartrate (KHT) holding capacity of model solutions.
- Solutions varied for proteins alone, tannin concentrations and ethanol levels.
- Minicontact and saturation temperature test measure the KHT holding capacity.
- We hypothesized an effective crystal surface coating action in proteins alone.
- For tannins a crystal surface fouling action is described.

To identify the interactions among individual molecules of the wine colloidal matrix and the potassium hydrogen tartrate crystal growth surface, the effects of proteins alone and of 1:10, 1:30, 1:50, and 1:80 protein:tannin concentration ratios on the tartrate-holding capacity of wine model solutions with 10, 12, and 14% v/v ethanol content were assessed. The results confirmed a reduced tartrate-holding capacity as the alcohol content increased, in contrast with an increased tartrate-holding capacity as the protein:tannin ratio decreased. The increasing tannin concentration shifted the value of saturation temperature (Ts) lower, narrowing the supersaturation field, whilst the presence of proteins alone increased the supersaturation field, shifting its right-hand edge towards a greater Ts value. In proteins alone, an effective growth crystal surface coating action enhanced by the electrostatic forces is postulated, whilst for tannins, a crystal surface fouling action by means of H-bonds weakened by the negative charge of the hydrogen tartrate ion is described.