When I decided to write a book about chemistry in our everyday life, I knew I needed a chapter about happy hour. Now, as I write, bars are closed due to the COVID-19 pandemic. Still, there’s no better way to end the day than hanging out with friends, telling stories, and buying cheap drinks. On sunny days in Texas, I go straight for some queso with a frozen margarita, but on date night, I tend to drink a glass of wine (or two). My husband always orders a whiskey before switching over to a refreshing beer; I can’t wait for life to go back to normal again.
But no matter which cocktail you’re drinking, every one of them is loaded with chemistry. Let’s start with the basics.
Alcohol is the generic name for a molecule that has a bond between a hydrogen atom and an oxygen atom, where the oxygen atom is directly connected to a carbon atom, like this: C–O–H. For example, methanol is an alcohol because it has the molecule formula CH3OH. Ethanol is an alcohol because it has the molecular formula CH3CH2OH. (The unbolded hydrogens are bonded to the carbon atoms, not the oxygen atom).
Depending on the context of your conversation, alcohol (or alc–OH–ol, if that’s easier to remember) can be the nickname for several different molecules. For example, at the doctor’s office an alcohol could be rubbing alcohol (isopropyl alcohol or isopropanol). In Asia, alcohol can be used as a fuel (methyl alcohol or methanol). In a margarita, alcohol is the molecule that gets you drunk (ethyl alcohol or ethanol). For that reason, I’m going to focus on ethanol in this chapter.
Oh, sweet, sweet ethanol. The way it reacts and bonds to molecules in our brain makes it a popular choice for after-work libations, first dates, and final breakups. But the process of how it is made is just as fascinating—and perhaps as surprising as why we enjoy it so much.
Historians are pretty sure that people have been making wine from grapes since 6000 BC and fermenting fruit since the Neolithic period. There is even a theory—called the drunken monkey hypothesis—that our brains have a natural attraction to ethanol because of something our ancestors did a long time ago: they ate ripe fruit (or fermented fruit) that contained ethanol, which created a natural attraction/joy response when we encountered the molecule elsewhere. In other words, in the same way that we have an inherent attraction to the smells and tastes of an apple or a banana (not because of their inherent “apple-ness” or “banana-ness” but because of the nutrients associated with them), we are also evolutionarily wired to be attracted to ethanol, once associated with those same nutrients.
We’ve long been experimenting with fermenting and separating those happiness-inducing ethanol molecules from the fruits and vegetables they occur in naturally. And we’ve got it down to a strong science, for the most part.
In general, wine is made in three steps. In the first stage, the grapes are picked from the vines, and then crushed to collect the juice. The machines that do this are actually quite delicate because they apply just enough pressure to break the skin to release the grape juice (called must), but not too much pressure to crush the tannins in the seeds at the center of the grape. After this, the stems are usually removed from the must because they have an unpleasant bitter taste. The remaining liquid part of the must is 12–27 percent sugars, 1 percent acids, and the rest is water. After placing the grape mixture in the proper container (with or without the skins), the best part of wine making can begin: the fermentation process.
Fermentation is an anaerobic process—or a chemical reaction that does not need oxygen as a reactant—that forms the molecule ethanol as a product. However, if oxygen is around during this process, the glucose will react to form ATP (as we learned in the fitness chapter), instead of producing ethanol.
But when oxygen is not around, yeast and sugar can react to form the alcohol. I bet you are familiar with this process if you have ever made bread from scratch before. The very first step is to activate yeast by letting it sit in sugar water for a few minutes. During this time, the yeast breaks the glucose molecules apart into smaller molecules, including carbon dioxide gas. That’s why, after enough time has passed, you should be able to see a light brown bubbly concoction floating on top of the water.
When making wine, this exothermic reaction—meaning heat-releasing—converts glucose (sugar) and yeast into ethanol and carbon dioxide, as shown below:
Glucose + Yeast → Ethanol + Carbon Dioxide
The product, pure ethanol, should actually have a bitter taste and it is extremely flammable. If someone ever tries to convince you to take a flaming shot, please politely decline and get as far away from the flames as possible. That kind of recklessness can set the entire building on fire—or worse, your face—just with one slip of the hand.
But if the ethanol is not set on fire and is allowed to continue to ferment, it will turn into acetic acid (vinegar, the cleaning product). Gross, right? That is the reason why it is important for winemakers to stop the fermentation process at the right time. Otherwise, the resulting wine will have a lovely sour vinegar taste.
The type of yeast used varies, which is another reason why different wines have different tastes. Some winemakers use yeasts that naturally exist on the skins of grapes, whereas others prefer to use a starter culture of yeast.
These fermentation starters—also known as mothers—are basically giant bowls of good fungi that self-replicate. The single-celled microbes react with the natural sugars that exist in the grape juice to release carbon dioxide gas. During this process, our beloved ethanol is formed as a byproduct.
These yeast starters are typically kept in cold environments and can be passed down from generation to generation. There are stories of old Italian grandmothers sneaking their delicious-tasting starters onto transatlantic ships to make sure they were passed on to their grandchildren. These yeast starters were usually used for bread, but the science is the same for alcohol.
Red wines ferment (in other words, the yeast reacts with the grape juice sugars, producing ethanol and carbon dioxide) for anywhere between four days and two weeks before the skins are finally removed. They continue to ferment until two to three weeks have passed (total). White wines, however, need about four to six weeks for fermentation, since they do not have any of the natural yeasts available on the grape skins. Sometimes, if the winemaker wants to add a practice called malolactic fermentation, they do it here in the second step.There are stories of old Italian grandmothers sneaking their delicious-tasting starters onto transatlantic ships to make sure they were passed on to their grandchildren.
Malolactic fermentation has been around since the discovery of wine, but in the 1930s, an enologist named Jean Ribéreau-Gayon accurately described the chemical reaction that occurs when malic acid (which exists naturally in most fruits, including grapes, and gives them a mildly sour taste) is converted into lactic acid. This decreases the taste of tartness in the wine. From what I can tell, each winemaker has a very strong opinion on whether malolactic fermentation is a good or bad thing. Some encourage it by introducing Leuconostoc oenos bacteria into their wine, while other winemakers do everything possible to ensure it does not happen.
Ever since we invented wine, we’ve been playing with the process, the colors, and the tastes. Historians believe that the first wines were all red, until the Egyptians found a color mutation—and process—that produced white wines. Red wines, of course, are only light red to start, and get their deep color (and unique flavors) from sitting on the skins during the fermentation process. White wines only soak in the skins and seeds of the grapes for a few hours, and then the juice is removed.
There are also a few neat subcategories that mix the two techniques together. For example, pink wines—called rosé—come from red wine grapes that are made like white wines. The maker does not let the liquid sit on the skins very long, which is why the resulting wine has a nice pink color. Orange wines, on the other hand, are white wine grapes that are made like red wines. This wine mixture also sits on the skins during fermentation, allowing for the wine to turn into a cool orange color. The longer the juice sits on the skins, the darker the color will become.
In California, most white wines (other than chardonnay) are fermented in stainless steel, which has no interaction with the liquid inside. However, red wines (and chardonnays) are often put into barrels. The type of barrel (American oak, French oak, even barrels used for bourbon) is what deepens the flavor.
In this last step, the wine matures and develops its intense layers of flavors. This process greatly varies for each type of wine and by each winemaker, but in general, some sort of wine racking occurs. A barrel of wine is set on a big rack, kind of like what you would see in a warehouse. The barrel is moved occasionally but the purpose of racking is for any solid particles to separate from the rest of the (liquid) wine. These particles would slowly sink to the bottom of the barrel, allowing them to be filtered out. Each barrel of wine is filtered several times while it’s racked.
This process of filtration is one of the most fundamental techniques used by any synthetic chemist. In the lab, we are constantly purifying our products by dissolving them in a liquid, and then filtering out any remaining solid particles. When winemakers rack wine, they are doing the exact same thing by filtering the wine over and over again, but on an extremely large scale. During this process, they are attempting to remove any remaining grape fragments and dead yeast cells.
At the very end of racking, the wine can be fined. This is when the winemaker adds a fining agent to the wine, like activated carbon charcoal or gelatin from fish bladders, which forms IMFs with the remaining solid particles in the wine solution. The resulting compound is too heavy to remain suspended in the liquid, therefore it sinks to the bottom of the container.
When the wine is finally ready, it is bottled and fitted with a cork. The best wines do not have a large gap between the top of the wine and the bottom of the cork. This is because the molecules in the wine can oxidize—or perform a chemical reaction with the oxygen gas in the air gap above the wine. Unfortunately, this is the worst thing that can happen to a bottle of wine because it causes the overly sweet smell that we associate with “corked” wine.
This is also the reason why wine is stored on its side, to prevent oxidization. When the bottle is on its side, the liquid keeps the cork wet, which allows for the cork to continue protecting the wine from the oxygen in the atmosphere. However, if the wine is stored in the vertical position, the cork can dry out, and then tiny oxygen molecules can sneak through the air pockets in the cork to get into the wine and ruin it. The smell of the cork can be used to check the integrity of that particular bottle of wine.
Ever since we invented wine, we’ve been playing with the process, the colors, and the tastes.
Once the wine has been opened, the same oxidation process will occur. That’s why you may detect a difference in the flavor of your wine between day one and day two. After that, as long as you keep your wine corked, it should keep for another three to four days. But as we just discussed, all wines are different, therefore you may need to perform a small smell (or taste) test on questionable wines. Generally speaking, after five or seven days, uncorked wines are better for cooking.
These days, more and more wines are bottled with a screw cap instead of a cork. I asked a sommelier about this when my husband and I were on our five-year anniversary trip to the Basque Country in Spain. He explained to us that the selection of a screw cap versus a cork is directly related to the aging process of the wine. If the wine needs to age for a long period of time, the winemaker will likely use a cork to preserve the oxygen concentration in the wine. However, if the wine is going to be opened and consumed right away, like an Oregon pinot noir, then a screw cap is just fine.
Champagne and more expensive sparkling wines especially need to be corked because they have a secondary fermentation process. Here, the yeast is converted into ethanol and carbon dioxide, but unlike the first fermentation process, the carbon dioxide is now trapped inside of a closed container, rather than being released into the atmosphere like with a traditional wine. This process takes at least two months and may last for a few years. When the yeast cells inevitably die, they provide the sparkling wine with a distinctive roasted flavor. The solid particles are once again removed after the fermentation process is over, and then the sparkling wine is recorked.
Even inexpensive sparkling wines that are pumped full of carbon dioxide gas (rather than using the carbon dioxide produced during fermentation) and stored under pressure—in the exact same way that sodas are carbonated—need to be corked. A screw cap cannot withstand the amount of pressure within the bottle, which means that the sparkling wine could unexpectedly shoot out of the bottle, like Old Faithful, at any moment in time.
A permeable cork, on the other hand, allows the sparkling wines to slowly release carbon dioxide into the small gap between the wine and the cork. It still builds up a lot of pressure, which is why you hear a pop when you open a bottle.
When my husband and I traveled to Spain, we developed a slight obsession with cava, which has been dubbed the “Spanish champagne.” It’s become our tradition to start our date nights or celebrations with a round of cava, and our friends have started to notice. In fact, at a recent happy hour, we shared a few details of our trip with our friends—one of whom happened to brew beer as a hobby—which led to a great conversation about the differences between wine making and beer brewing. Of course, in the pursuit of tasty liquid + ethanol, the processes are very similar.
While wine uses the simple sugars in grape juice to react with yeasts in the fermentation process, beers use complex sugars (like starches from grains) as their starting materials. But starches need to be broken down into smaller molecules before they can be used for anything useful. So, what do we do?
We cook them.
Excerpted from It’s Elemental. Used with the permission of the publisher, Park Row Books. Copyright © 2021 by Kate Biberdorf.