Where Wine Gets its Kick

By pure volume, America has become one of the largest consumers of wine in the world. Twenty years ago, Americans produced about 440 million gallons of wine, and the average person in the US drank about two gallons of it a year. In 2016, though, Americans produced 800 million gallons of wine, and the average American consumed nearly three gallons.  Wine is one of the oldest beverages consumed in the world, and although its industrial-scale production has matured drastically in the past century, the roots of wine-making have scarcely changed since 8000 BCE. Let’s pour ourselves a glass of chardonnay (or pinot noir or rosé) and talk about the history and science behind this hallowed drink.

A Brief History of Wine

It’s hard to say exactly when humans started making wine, but the earliest known wine vessels were discovered in Georgia (that’s the one near Russia, not the one in the United States!). These vessels have been dated to somewhere between 6000 and 8000 BCE, which means wine-making is almost 10,000 years old – predating Mesopotamia! Wine’s long history is likely a consequence of how easy it is to produce, since wild grapes naturally collect yeast, a crucial ingredient for the fermentation process. In fact, wine may have been discovered accidentally after someone left an old grape container outside for too long, only to taste it and discover its richness.

Though wine has been drunk throughout history, notably in ancient Greece and Rome, all the way through the Renaissance, it wasn’t until the advent of the industrial tools and microscopes of the 18th century that we developed an understanding  of the science behind the drink. It all started when the French government assigned Louis Pasteur (after whom the process of sterilizing milk was named) the task of discovering how and why certain wines spoil. His work uncovered an entire new area of food science: the chemistry and biology of wine.

The Chemistry of Wine’s Taste

Glucose is the sugar found in grapes. The yeast use one sugar molecule to make two ethanol molecules and two carbon dioxide molecules. Tightly sealed wine has fizzy bubbles – they’re from the carbon dioxide gas.
Image: Generated in ChemDraw

Wine contains many ingredients, but the one that raises it above other fruit drinks is ethyl alcohol, or ethanol. Yeast that live on grapes create ethanol (along with carbon dioxide) by fermenting sugar. Eventually, the yeast create so much ethanol that they poison themselves and die off.

While ethanol is what gives you a buzz, many other chemicals in wine contribute how your glass tastes. For instance, if the yeast are removed early or killed off before they finish fermenting all the sugars, your wine will be sweeter. To make these sweet wines, some growers will add sulfur dioxide to the wine, which kills off the yeast. This chemical also adds a bit of a flavor, and some people are allergic to it. Yeast also produces a variety of other byproducts, which all contribute to the wine’s flavor and texture. These include:

• Glycerol, which makes hearty red wines slide slowly down the glass when you give them a swirl
• Methanol, which will give wine a flat taste
• Acetic acid, which is found in vinegar and breaks down into ethyl acetate and smells like nail polish
• Hydrogen sulphate, from the sulfur dioxide, which gives off a scent like rotten eggs.
• Isoamyl acetate, which taste like bananas
• 4-ethylphenol, which smells like band-aids
• 4-ethylguaiacol, which adds a smoky or spicy aroma.

Finally, some taste comes from the grapes themselves. Different grapes grown in different climates or regions will affect the taste differently. Sommeliers, or wine experts, are trained to detect subtle hints of minerals from the water used to grow the grapes, as well as other slight aromatic components that you’ll find listed on the label (such as hints of chocolate, citrus, or pepper). Two ways to impart flavors into a wine are to 1) age the wine in an oak barrel (giving off the oaky taste found in chardonnays) or 2) control how long the wine ferments with its skins present. The skins release tannins and give off a rich and somewhat sour taste.

The Microbiology of Yeast

In the wild, yeast naturally colonize on the skins of grapes. In a vineyard, you might notice a dusty powder on the grapes – that is the yeast. The main strain of yeast found in wine-making is the same that we use to make bread and beer: saccharomyces cerevisiae. These yeast thrive at low pH, around 2.8-4.0, which is about as acidic as a glass of orange juice. Other yeast strains may be present, but they cause problems for growers – they give off stinky byproducts – so growers usually kill them off with low levels of sulfphur dioxide. There is always a balancing act between eradicating the unwanted yeast and allowing s. cerevisiae to thrive.

Wild grape skins are covered in a powdery substance. This substance contains the yeast that ferment sugars into ethanol.

As I mentioned, yeast use the sugars that naturally occur in grapes to grow and reproduce. By crushing the grapes, growers allow the yeast access to more of the sugary juices, letting the fermentation process begin. Yeast die off once the grape juice reaches about 15% alcohol by volume, although some grapes with high sugar content can naturally produce wines of 17-20%.

Where Wine Gets its Color

Walk into your local Binny’s and you’ll find a huge selection of wines that range in color from almost clear to brown-red. Color in a wine comes from the grape skin. Most grapes, regardless of the color of their skins, produce a green-white juice when their skins removed. Though white wines are generally still made from the green or white grapes, they are usually still fermented without skins to avoid the tannin taste that makes a wine feel ‘heavy.’

Trendy right now is the rosé wine. Growers give rosé gets its pinkish color by removing the skins shortly after the fermentation process starts. Some producers also make rosé by combining red and white wines to make pink, but this is considered quite the faux pas in the wine world.

Wine Across the World

Though wine is not as popular as beer or certain liquors, it has demonstrated a staying power across millennia. Today, Italy is the largest producer of wine (the US comes in at #4), while France is the greatest consumer, at 2.15 gallons per person per year. Americans don’t even break the top ten on the list of the greatest consumers! Nonetheless, it’s difficult to imagine a classy party without a selection of vintages for the guests. So next time you drink one of the 8.1 billion gallons of wine made in the world this year (hopefully not all in one sitting), take a moment to swirl your glass and consider all the science that brought this delicious drink to your home.

Stefanie Kall is a Ph.D. candidate in biochemistry at the University of Illinois, Chicago.