question for the scientists here (or anyone who knows the answer)

Why is surface tension different for Riesling-based wines, or sweet wine in general, than for, say, Bordeaux blends, in a way that conduces seepage past the closure?
 
originally posted by Ian Fitzsimmons:
Why is surface tension different for Riesling-based wines, or sweet wine in general, than for, say, Bordeaux blends, in a way that conduces seepage past the closure?
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It's not Riesling, it's sugar and alcohol together. So Andrew's real rabbits leak just as well as the Auslesen in the fatcave.
 
I imagine stronger tension would allow seepage along the side of the cork to maintain continuity with the reservoir of liquid beneath the closure, eventually leading bits of it all the way past the top.

Screwcaps.
 
originally posted by Arjun Mendiratta:
Ian, what you are describing is the behavior of a liquid with low, not high, surface tension.
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Break that down for me, Arjun. With low surface tension, the liquid would cease to draw, wouldn't it?
 
Ian, surface tension refers to the tendency of a liquid surface to stay intact. It is a consequence of the cohesive forces between molecules at the surface. If these forces are strong, as they are for water, the liquid is said to have a high surface tension. Surface tension can also be thought of as the energy required to create additional surface area, i.e. to move liquid from the bulk to the surface.

The seepage of liquid into the gap between the cork and the bottle, or into any small pore, is ultimately a competition between the wettability of the pore surfaces, which acts to pull liquid into the pore, and surface tension, which acts to prevent expansion of the exposed surface area. As a result, liquids with high surface tension are less likely seep into small pores than liquids with low surface tension, all other things being equal.

For example, if you have a fine sieve, you may be able to "float" a droplet of water on top of it, whereas a lower surface tension liquid like rubbing alcohol will penetrate the pores of the sieve.
 
So capillary action draws the liquid past the cork while internal cohesion impedes its progress; ergo diminished surface tension = more rapid seepage. Makes more sense than what I wrote, assuming the capillary action is not hugely stronger than the internal cohesion, and that the presence of sugar in the solution, in addition to the alcohol and other wine stuff, does diminish cohesion.

Fwiw, I have a fair amount of German wine and encounter seepage so rarely that I've always attributed it to high fill plus careless handling. On the other hand, I've only encountered in dry wines two or three times ever (and then high fill again seemed a likely culprit).
 
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