by Arthur Z Przebinda
Continuing in the discussion of common wine myths, let’s look at the ideas of breathing wine and “legs”. Interestingly, both have something to do with surface area.
Different types of chemical interactions occur in wine depending on whether it is exposed to oxygen. In general, oxygen allows the wine’s aromas to “open up” or become more prominent and balanced. This happens because exposure to oxygen is minimized during modern wine production and, once in the bottle, a wine’s aroma molecules are tied up or stick to other molecules. Introducing oxygen, allows those aroma molecules to free themselves and escape the wine.
And here we come to the myth of “breathing” a wine simply by pulling the cork and letting the bottle stand for some time. In that situation, the surface area of the wine exposed to air (in the neck of the bottle) is about the size of a quarter. That is like a human trying to breathe through a coffee stirrer.
Decanting, which is simply the action of pouring a wine from its bottle into another container, separates the wine from any sediment and increases the surface area of the wine. This means more wine is being exposed to oxygen. The wine takes up this oxygen as it is poured, and the oxygen liberates the aromas. A whole slew of spouts and funnels have been invented and produced to increase the wine’s surface area as it is poured into a decanter. Surface area is also why decanters are often wide-based: there is more wine exposed to oxygen as it sits in the decanter.
Historically, though, this practice served an additional purpose. In earlier days, much more sulfur was used in wine making than is used today. Sulfur preserves wine by killing bacteria – particularly those which can spoil the wine once it’s in the bottle. But this occasionally led to some wines having an off-putting smell. Decanting, by increasing the wine’s surface area, allowed those sulfur molecules which were not chemically attached to the components in wine to escape from the wine.
If wine needs a lot of room to breathe, its legs won’t cover much ground. Also called tears, they are viscous, tear-like tracks running down the inside of a glass after you swirl the wine. Despite their oily appearance, they have nothing to do with glycerol. Visually pleasing, they do little to indicate a wine’s quality, but are a fun demonstration of the Gibbs Marangoni Effect – named after two scientists who described the principles responsible for shampoo, beer foam and sheeting action of dishwasher detergents.
Water clings to glass because of the attractions between the molecules making up the two. Looking at the side of a glass of water you will see a meniscus - an upward curve of the surface of the water along the inside of the glass. It doesn’t go up very high because the forces attracting the water to the glass are minimally stronger than the attraction of water molecules to each other.
The alcohol in wine helps overcome the attraction of water molecules to each other and allows a film of wine to cling to the glass after swirling. Although it is dissolved in the wine, alcohol evaporates from wine faster than water does. This happens rather quickly – especially since the film of wine on the inside of the glass has a large surface area. As a result, there is a greater proportion of water in the film and the attraction of the water molecules to each other overcomes their attraction to the glass. The wine forms drops which are too heavy for water’s attraction to glass to hold them in place and they flow down the side of the glass.
Some will attribute the legs phenomenon to the wine’s glycerol content but this substance is present in trace amounts in wine, evaporates at higher temperatures than either water or alcohol and doesn’t contribute to the formation of legs.
Arthur Z. Przebinda
Arthur is the founder, editor and sole wine critic for redwinebuzz.com, a web site he established in 2006 offering general wine information with an emphasis on education and opinion about California's Central Coast wine region, wineries and winemakers. He is also the author of the blog winesooth.com
Arthur has created educational content and other materials used at wine festivals. He has been consulted as a wine expert by wineries. His articles have been featured on several wine web sites. He has been a featured columnist on Appellation America and has contributed commentary to the Los Angeles Times’ “Blowback” section.