Don Warrington, of Dunedin, asks :-
When finishing pouring wine, red drips more than white. Why is this?
Bernard Newman, a wine scientist at Lincoln University, responded.
There would be three main contributors to viscosity; yeast, alcohol concentration and residual sugar content.
With respect to surface tension, I am not sure how variable this is in aqueous solutions and whether or not the variability between wines would account for any visible effects here. The glycerol that yeast produce eventually finds its way into the wine and I suspect there is little difference in concentration due to the traditional ferment differences of red (a warm and fast ferment of 5-7 days) with that of most white wines (being cooler and slower).
Some white wines are aged on their lees, with yeast autolysis over time contributing flavours, but I don't recall any reading to suggest changes of viscosity being associated with this treatment.
Alcohol concentration in wines may range from 9% - 15% and both red and white wines have variable levels of alcohol. So this is not a guide.
Residual sugar (or additions of sugar) will contribute to viscosity. Obviously a wine having a sugar level similar to that of golden syrup will have a similar viscosity too. Typically, red wines are fermented to dryness and so we would not experience a higher viscosity effect due to residual sugar in red wine. If dry wines are less viscous, then we should see equal 'drippyness' in both red and some white wines.
Some dessert wines have relatively high residual sugar levels. A wine in this category could well have 200 g/l of residual sugar. If residual sugar is a significant influence then we would expect desert wines (these are typically white wines) to exhibit higher viscosity and less of a tendency to drip when poured. Alcohol concentration could modify the residual sugar effect so one could well have a high sugar + high alcohol wine (eg some Port style wines) exhibit low viscosity but still exhibit palate 'weight'.
Perhaps 'dry matter extract' could directly correlate to wine viscosity. An opportunity for a research project perhaps?
It may just be that red wines appear to drip more than white, simply because it would be easier to notice the red drips once they have dropped.