3.1. Surface and interfacial tension measurements
Surface tension values of the aqueous phase of an emulsion are indicatory data of the emulsion stability with time. Table 1 shows the corresponding values for each emulsion of the study. An alcoholic solution with 12% or 13% (v/v) ethanol has surface tension values γ = 49.5 mN/m and 48.1 mN/m, respectively [10] and [11]. In Table 1 it is shown that the surface tension values for 100% (v/v) wine with alcoholic grade around 12.5%, which is the average alcoholic grade of the two wines used in this study, are considerably lower than the above reference values. Even more surprising is the fact that the red wine exhibits higher surface tension than the white one (45.9 mN/m and 42.0 mN/m, respectively), although the former – being a red wine – has more phenolic compounds, proteins, etc. that could lower more its surface tension [11], [12], [13], [14], [15], [16] and [17]. This finding can be attributed to the fact that the white wine used in this study is produced from a Muscat grape variety which is known for its high content in aromatic compounds. In any case, even with small percentages of wine – whether red or white – in the aqueous phase, e.g. 5% (v/v), the decrease of the surface tension value compared to that of water is significant.