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Wine Tasting Science.

There’s a lot of science going on in your glass of wine, whether it's a Two-Buck Chuck or a Château Fancy French Wine—and everything in between! It brings together geology, viticulture, botany, chemistry, and even physics.

You can see it in action the next time you pour a bottle. After all, wine is a living thing that develops, ages, and goes the way of all vinegar.

Suffice to say that there’s a lot more going on in your glass than grapes and alcohol.

The 5Ss of Wine Tasting

If you’ve to a wine tasting, you’re probably familiar with the 5 Ss to learn and appreciate what’s in your glass. The first thing is to see, to notice the wine’s color, preferably against a white background. There’s a lot you can learn just by looking at a wine with this one simple step.

Then, you swirl the wine in your glass gently. That brings oxygen to the party. It’s a good thing, too, because of the next step that takes your experience to the next level.

Now, it’s time to sniff the scents jumping or slowly rising out of the glass. Your swirling helped to release these aroma compounds. Those are the organic chemicals that are behind the scents you’re detecting. Many have low boiling points, so it doesn’t take much for them to vaporize.

Some of the most interesting ones may occur in minute amounts but contribute a lot to the WOW factor of a wine.

Next comes the fun part. You sip the wine. You need to take a good-sized gulp (Duh!) and swish it around inside your mouth. Don’t swallow it right away. That warms up the wine, even more, allowing more aroma compounds to develop for you to experience.

The last step is the best one. You get to savor the wine and perhaps wax poetic about what you’ve tasted. Often, they are stronger impressions of what you’ve smelled earlier. Other times, they are something new.

As you drank your wine, you may have noticed a weird phenomenon, assuming it was from a clean glass. Little rivulets of wines moved slowly down the sides. If you tipped your glass or swirled it again, even more tears formed.

What you’re seeing is what the beverage industry calls wine tears. They also go by some other more imaginative names, such as cathedral windows, fingers, curtains, or legs.

It’s fascinating to watch because that’s one aspect where science and physics are on full display. Who knew?

What’s in a Glass of Wine

To understand the wine geek stuff or magic as some may call it, it helps to begin at the beginning—literally!

The process of going from grape to wine is deceptively simple. It even occurs in Nature with no one’s around to help. The sugar in the grapes increases, and the acidity decreases the longer they sit basking in the sunlight.

That’s why timing is so critical for winemaking. Balance is essential when it comes to the harvest.

The simple formula takes that sugar in the grapes and feeds it to yeast existing in the wild. If it stays warm enough, that’s when the magic happens, with about 30 chemical reactions driving the bus.

Cold and slow is the best scenario for a dry white wine. On the other hand, red wine likes it hot and fast, in the fermentation room, anyway.

The result of all this alchemy is alcohol, carbon dioxide, and heat. What ends up in your glass is:

  • Water
  • Alcohol
  • Sugar
  • Acid
  • Phenols

Phenols include a broad spectrum of goodies. They give a wine its color. They contribute to the delicious aromas you smell. They also can preserve the wine and add to its mouthfeel.

Other things like yeast, sulfur, and bacteria may be floating around, too, if you consider the total wine content. The point is that these are the ingredients for wine and spirits physics. They are the raw materials for the wine tears in your glass.

That’s where wine physics comes into the game.

The Why Behind Wine Tears

The principal players in wine tears are water and alcohol. They’re not evenly matched because there’s about 90 percent of the former and 10–15 percent of the latter, depending on the wallop of your wine. The interaction between the two liquids is the real story.

Surface Tension

The varying chemistry of the two liquids sets the stage. Chemical bonds hold the molecules of each of these components together. However, they react differently when they occur in wine.

You may have noticed how some insects can walk on water in ponds or puddles. That’s because of the chemical bonds holding the water molecules together and their collective force on the surface. It’s what science calls surface tension. It essentially acts as an invisible film over the water.

These two actions make it possible for that bug skimming along the surface. That’s also what explains droplets on leaves or other surfaces. The water molecules are sticking together and not to whatever is underneath them.

Surface Tension in Action

This same effect happens in your wine glass. The difference is the respective surface tensions of water and alcohol.

H2O has the higher surface tension of the two liquids, creating a gradient in wine. If you just mixed the two together, you’d create areas of greater and lower surface tensions. The flow of molecules will gravitate toward the areas where the surface tension is less concentrated.

An easy demonstration of science made simple will show you how it works. First, partially fill a plate with water. Then, sprinkle some ground black pepper on the surface. You’ll notice two things right away:

It floats.

The pepper is pretty evenly dispersed over the surface of the water.

Next, dip a toothpick in your favorite dish detergent. Touch the surface with the soap-coated tip. Don’t turn away or even blink.

The pepper scatters to the sides of the plate in an instant. Your next question probably is, is it the wine, or what just happened?

The detergent is the culprit. One of its amazing properties other than getting your dishes squeaky clean is that it is a surfactant. It can break the bonds holding the water molecules together and reduce the surface tension.

However, those bonds are still quite strong and want to hang together. That’s what causes the molecules to move away from the soap and toward the sides. The pepper just got stuck in the crossfire and came along for the ride.

The Marangoni Effect

Surface tension plays a role in wine tears with different results. That’s because, unlike the soap and water experiment, wine has a uniform consistency. It’s not like the alcohol is floating to the top. It’s everywhere in the liquid.

To see it close up and personal, swirl your wine glass again, noticing the wine tears on the side. They appear to slide up and then down back into the glass. Several things are going on to create the proverbial perfect storm.

When you first swish around the wine, it clings to the sides of the glass, forming an ultra-thin film. It’ll stay there, forming a ridge until it starts to fall back down under its own weight, drip by drip. Those are the tears.

What’s also happening is that the alcohol is starting to evaporate at these low concentrations of liquid on the sides. That’s the surface tension gradient revving up in your glass.

The wine tears have a higher surface tension because there’s less alcohol in them. Like the pepper demo, the water molecules are pulling more of the wine up the sides of the glass.

After a while, the wine tears slip back into the glass because the molecules are too heavy, chemically speaking. The really cool thing is that it keeps happening. When a wine critic speaks of it dancing in the glass, that is exactly what’s going on with your libation.

You can think of it as a group of people going up a staircase with a closed door at the head of the stairs. They keep going up and up until there’s a backlog. Then, everyone comes tumbling down over and over again. 

Physicist James Thomson described this sequence of events way back in 1855. Italian physicist Carlo Marangoni later got the cred and the name recognition because of his academic studies of the effect.

But, like all good things, wine tears come to an end, too. The other stuff in your glass, like the tannins and organic compounds, move in on the film on the sides and the water-alcohol show exits the stage.

The next question is, what can wine tears tell you about what’s in the glass?

Myths About Wine Tears

There’s no doubt that wine tears can say something about the beverage. But, like many things, you’ll come across both true statements, some misinformation, and some outright whoppers.

Wine Tears and Quality

Many myths about wine tears start with a discussion of the size, shape, and width of them. Supposedly, the thicker or fatter they are, the better the wine.

Unfortunately, that’s an old husband’s tale.

Wine tears speak nothing to the quality of a wine. That’s because they only tell you that it contains water and alcohol. Any wine that has a reasonable amount of ethyl will produce tears when you swirl the glass. That applies to your Barefoot Wine or Châteauneuf-du-Pape.

Wine tears can give you an indication that it’s leaded fuel of the high-octane variety, but that’s about it. One could argue that a higher alcohol content helps wine remain drinkable for a longer time or it has a decent aging ability.

True, but other things have an impact, too, such as tannins, acidity, and residual sugar, to say nothing of terroir, the grapes, and the winemaker. It’s just not that simplistic. Otherwise, there won’t be wine critics.

Glycerol and Wine Tears

Ethyl isn’t the only alcohol in your glass. Fermentation also brings along methanol, fusel alcohols, and glycerol. Each may contribute slightly to the viscosity of your wine. However, they’re not the money shot when it comes to wine tears.

On a side note, glycerol can give dessert wine a more unctuous mouthfeel and make a significant impact on its body. It may even make them seem sweeter since alcohol can create that sensation.

The Absence of Wine Tears

On the other side of the coin is the question of the lack of wine tears and its takeaway message on the quality.

The short answer is that it is hard to point any fingers.

Wine tears may sound simple, but many things can affect them. The percentage of alcohol is a major factor, of course. The absence may just mean it’s on the low side.

That’s because the gradient between the two isn’t high enough to make an impact. Then, there are external influences.

If you’re drinking wine outside on the patio in full sun, the alcohol that is in your glass may evaporate quicker—along with the water.

If you over-swirl, you might get the other components of wine into the game quicker and shortened the window for tears.

Finally, there’s that nasty elephant in the room, less-than-perfectly-cleaned glasses. And the thing contributing to those odd aromas in your glass are the same ones that reduce the surface tension.

Dishwater detergent residue can wreak havoc with wine tears. That’s why it’s essential to clean and rinse your glasses well. You can also use a product formulated for wine glasses.

Final Thoughts

Drinking wine is one of the most pleasurable experiences you can enjoy. It can mellow you out and help you release the tensions of the day. It can also stimulate conversations with discussions about its chemistry and physics that can make understanding it that much easier.

If you need a reason to enjoy a glass, think of it as a science experiment. It’s a terrific way to see these phenomena at work play. Raise a glass to James Thomson and Carlo Marangoni for allowing people to enjoy their wine with a keener appreciation of its magic.

Photo by Bill Oxford on Unsplash

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