Surface tension of still wines in relation to some of their constituents: A simple determination of ethanol content

An attempt is made in this work to establish a correlation between surface tension and analytical characteristics of still wines, with the aim of predicting mainly their ethanol, protein and tannin concentrations. First, model solutions of ethanol, bovine serum albumin protein (BSA) and tannins were prepared and their surface tension measured. Second, the analytical characteristics of 20 still white and red wines from Hellenic grape varieties were determined, using methods of titration, liquid and gas chromatography (HPLC and GC/FID) and spectrophotometry (UV–vis and FTIR). For the surface tension measurements of both model solutions and wine samples, the Wilhelmy plate technique was applied. Statistical analysis of the results showed that 12 enological parameters were highly correlated with surface tension. Ethyl alcohol, proteins, tannins, potassium, sodium, total phenols and methanol, as well as the volatile acidity and pH of the wines, exhibited negative correlation; while total SO2 and malic acid had positive correlation coefficients at a confidence level of 95%. The best linear model was obtained for the ethanol content, as it can predict by 91.4% the alcoholic strength of a wine based solely on its surface tension. This work, for the first time, provides a simple and fast way of estimating the value of such an important enological parameter.