Editor’s Note: Today’s guest post is by Chris Gerling and Anna Katharine Mansfield, who direct the Cornell Craft Beverage Institute at Cornell AgriTech in Geneva, NY. In honor of our special exhibition Fire and Vine: The Story of Glass and Wine, we asked them to tell us a bit more about how glass is used to make wine.
On the face of it, ‘wine’ and ‘laboratory’ don’t have a lot in common – one’s an agricultural product steeped in history and tradition, and the other is the sterile domain of lab-coated scientists. As it turns out, the art of wine involves a lot of science, and the science of wine involves a lot of glass! Even the least scientific among us are familiar with the cartoon images of wildly-shaped glassware full of brightly-colored bubbling liquids… and, yes, the wine lab has stuff like that. But we use glass to analyze grapes and wine in all sorts of unexpected ways, starting in the vineyard.
The first step in winemaking is deciding if grapes are ripe enough to pick. There are some obvious tells, like tasting pretty good and changing color from green to red. When grapes are ripening, they accumulate the sugar that’s eventually fermented into alcohol, so we want to make sure they’re fully ripe and at peak sweetness. To measure sugar more accurately than by taste, we can squeeze a few drops of grape juice onto a refractometer, a hand-held instrument that measures how liquid placed on a prism changes the direction of light. These refraction angles can be correlated to the concentration of sugar in the liquid, which we express in juice on a scale of °Brix (roughly, percent sugar).
If we squeeze a little more juice from a larger sample of grapes, we can test sugar concentration by using an instrument called a hydrometer. A hydrometer looks a bit like a glass thermometer with a big bubble in one end and is calibrated to float at different heights in liquids of different density. Grape juice isn’t dense because it’s been skipping school, but because it contains sugar, and the more sugar dissolved in the juice, the greater the density, and the higher the refractometer floats.
Ripening isn’t just about accumulating sugar. Grapes also lose acids as they mature, so we measure acidity at harvest to ensure a balanced palate. Titratable Acidity (TA) in wine is assessed by titrating the wine with a base solution of known concentration – that is, adding the base drop by tiny drop until we reach a given pH. To accurately release and measure the volume base, we use a burette, a long, skinny graduated glass tube with a precision stopcock at the bottom, to drip solution into a beaker that’s being stirred or swirled.
Once the grapes are harvested and crushed, all we have to do is stand over the tank and tell the juice how no one understands us and how we can’t seem to find socks that feel comfortable both in and out of shoes and why no team from Buffalo can ever win the big game. No, sorry, that’s “whining.” We need wine. Converting juice sugar into alcohol is a big job that requires really tiny workers, specifically, yeast. Commercial yeast comes freeze-dried and is rehydrated and added to the juice to start fermentation. We can guess it’s started when the juice is bubbling and the tank is getting warmer, but what if that just means the yeast are all sitting around in tiny hot tubs to warm up after the freeze-drying? To monitor yeast progress, we can take a few drops from the tank and place it on a glass microscope slide. With the aid of the (also glass) magnifying lenses in the microscope, we can make sure the yeast going about their business, with no evidence of tiny hot tubs.
Once the yeast have converted all the sugar into alcohol we technically have wine, but there are still several production processes before we put it in a (glass) bottle. We may want to filter, blend, or age, which will take time. To protect the wine from oxidation and spoilage during this period, we might add a carefully-measured dose of sulfites…but not too much, or we’ll introduce a stinky sulfur aroma to the wine. This is where our weirdly-shaped glassware comes in! We use an aeration/oxidation (A/O) assembly, a convoluted series of glass flasks and tubes, to measure the sulfite level and contribute the bubbling, color-changing feel any serious laboratory should have.
All this stuff is fairly routine, but sometimes we want to run really specialized tests. For instance, if we send a wine off to the prestigious tasters at Better Wines and Vineyards and they write a glowing article raving about the amazing lychee aromas, we…wait, what? There weren’t any leeches in this wine. Oh, LYCHEE, the tropical fruit…but we didn’t add that, only grapes and yeast! It turns out that wine smells like all sorts of things, from fruit to green pepper to vanilla to tobacco to…well, all sorts of things….because many of the same compounds found in grapefruit or green bell peppers, etc., are also found in wine.
If we want to know exactly what compound is producing a certain aroma, we measure it by injecting a few microliters of wine into a gas chromatograph (GC) column, which is essentially a 30-meter-long glass tube with a very tiny diameter that’s spooled onto a coil and subjected to intense heat. As a superheated wine sample turns to gas, the individual aroma compounds are separated from one another and identified as they pass by a detector at the end of the column. This is how we know that wine can contain the same aroma compounds as berries or grapefruit or peach, all due to the action of yeast during fermentation. Kind of sorry you took away their hot tubs, aren’t you?
Making wine is both remarkably simple and incredibly hard. On one hand, it’s essentially great-smelling spoiled grape juice; on the other, it’s the result of complex biochemical reactions involving thousands of metabolic pathways. Winemakers are artists who trust their senses to make stylistic decisions, but the decisions are informed by sound measurements of grape and wine parameters. Precision glass instruments aid these measurements, so when the wine is poured from the glass bottle into the stemmed glass, all we smell and taste are the things we want to be there.
We’ll drink to that!
Fire and Vine is on view in the Gather Gallery at The Corning Museum of Glass until December 31, 2022.