Finally did some research into the “legs” or “tears” that appear on the insides of your glass of wine. I had been educated enough to know that these had no marking on the quality of the wine and had something to do with the body of the wine, but not much beyond that. So what are they all about?
Evaporation
The alcohol in wine evaporates at a faster rate than the water. It also has a lower surface tension. So I don’t get too Geeky, the simple explanation is that beads are building up on the sides of the glass as evaporation occurs and then they fall when gravity takes over to cause the “leg” or “tear” to fall down the glass. I find they are best looked at when there’s a flickering candle on the other side of the glass.
In terms of quality, the percentage of alcohol in the wine is noted (i.e. 13.5%), but more importantly it’s balance to the remaining factors of the wine (acidity, tannin, etc.). However, because the “legs” are created due to the processes of evaporation and gravity there is no way to relate the visual information with the gustatory or olfactory information you are about to receive.
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So, if the wine takes longer to slide down the side of the glass, does that mean more or less alcohol? And how does the sugar content affect this?
Generally, the more legs or the more prominent they are would indicate a higher alcohol content. Look up the Marangoni effect for more info. on that. Sugar content (residual sugar left over from halted fermentation) will have no effect on this.