One of the most common questions posed by those who begin to delve into the world of wine concerns the thin and thick streams of liquid that flow down the inside of the wine glass. The two expressions in the title—wine legs or wine tears—are used to describe these streams. The purpose of all discussions on this topic is to understand whether these flows are indicative of the quality of the wine. So, what kind of flow suggests a high-quality wine?

Let's first try to understand the fundamental physical reality behind these flows and then evaluate whether there are sufficient conditions for making a judgment. The flows we see in the glass are shaped by the chemical composition of the wine, temperature, humidity, and the shape of the container. Let's explore how this process occurs.

When we swirl the wine in the glass, a thin film of liquid covers the inside surface. This thin layer contains both alcohol and water molecules. As the volatile alcohol quickly evaporates into the air, water molecules and the heavier tannin and sugar molecules form droplets on the inner surface of the glass. These droplets, under the influence of gravity, trickle down, creating what is known as wine tears or legs.

For the curious, this phenomenon is known in physics as the Gibbs-Marangoni Effect, named after the scientists who developed the theorem. In summary, the formation of these flows arises from the differences in surface tension between liquids.

Now, the main question: Can we infer anything about the wine by looking at these flows? Without any margin of error, you can say that these flows are proof of the wine's alcohol content. But, we already know that; we don't need the legs or tears to reach this conclusion.

If we delve a little deeper, we can say that since the droplets consist of water, sugar, and tannin molecules, these characteristics are more pronounced in wines like red wine or sweet wine. However, we must remember that this information doesn't strongly indicate whether the wine is good, bad, or of high quality. It is also worth noting that the shape of the glass affects these flows. The same wine will produce different flows in glasses with different oval angles.

In conclusion, the wine tears we see in the glass give us an idea about the structural characteristics of the wine, but they do not tell us anything about the quality of the wine.