This guy is flying drones and building Arduino temperature sensors to make better wine

Credit: Mary Branscombe

Ryan Kunde's winery, DRNK Wines, doesn't look like a hub of technology. It's hidden away on a quiet drive on the outskirts of Sebastopol, down an unmarked turning: "We can be hard to find", Kunde warns us, but we only get lost once. When we get the right turn, the winery nestles between vineyards (pinot noir and chardonnay) and a golf course. Wild turkeys roam between the poppies on the meadow slope that conceals DRNK's 320-foot wine cave, dug by one of the borers that made the Channel Tunnel and lined with Shockcrete to control the humidity.

That's not the only technology on display. The silvery fermentation tank by the doors to the wine cave sprouts cables and power leads -- an Arduino-based temperature sensor loop Kunde slides in so he can monitor what's going on inside the two-ton tank.

Temperature matters

What goes into the tank is a mixture of grape skins, grape pulp, and grape seeds. When this starts to ferment it produces CO2 that floats the lighter skins up to the surface, forming what's called a cap over the grape must, while the seeds float to the bottom. The grape pulp gives you water, sugar (which feeds the yeast that causes fermentation), and acid, but that's only part of what gives wine its flavor.

Tannins from the seeds and skin play an important part, as do the anthocyanin pigments in the skin which give the wine its color. And the tannins you get from the grape skins are different from those in the seeds; they're longer molecules, they're present in different proportions, and they give the wine a different flavor profile and "mouth feel" explains Kunde, giving us a lightning tour of wine science. "It's the way it binds to the saliva in your mouth".

The temperature inside the tank has a major effect on how the wine turns out. "A higher fermentation temperature means you get more diffusion from the seeds and more extraction of tannins." It also determines how quickly the yeast turns sugar into alcohol. "For every ten degree increase in temperature you get a doubling of the fermentation rate."

Credit: Mary Branscombe

Between the energy that comes from fermentation and all that CO2, the temperature isn't the same throughout the tank; the difference between the cap of skins and the liquid must can be as much as 14 degrees. Depending on the style of wine you're making, you might want the cap of skins to be cooler than the grape must, warmer or at the same temperature, and you might want the must to have less contact with the skins in the cap or a wider surface area where it's exposed to oxygen. To control that you might push the cap down into the tank or pump liquid from the bottom of the tank and pour it over the cap. But how do you know when to do that?

Different wine makers have their own techniques. Kunde wants to measure the temperature inside the tank. Hence the sensor, which he built with parts from a home improvement store and an Arduino board. He can track the temperature at different levels in the tank over time; if the cap is too cool, he knows whether it's been like that for half an hour or all night, so he knows what he needs to do to the tank.

But it's not just about managing the individual tanks as he makes each wine. He wants to take the temperature measurements from the tanks and use them the way wine makers already use a measurement called "growing degree days": whether grapes have had enough days when the temperature is between 50 and 86 degrees (10 and 30 degrees C) to ripen well. Kunde has USB data loggers monitoring the temperatures in all the vineyards where his grapes grow; the figures go into an Excel spreadsheet he can refer back to. Now he's working on calculating an equivalent temperature calculation, including the range of temperatures for the must and difference in cap temperature, for managing fermentation.

Using drones to monitor the health of the vineyards

The data loggers aren't the only way he keeps an eye on his pinot noir and chardonnay grapes, which are not from the slopes around the winery. He buys from contract growers in the Russian River Valley, at the southern end of Napa, in Annapolis in Sonoma, and two hours' drive away in Mendocino. He can't walk through the vines every day, the way a wine maker with his own vineyards can. Instead he regularly flies drones over the vineyards, using cameras to capture video and even infra-red imagery and he uses satellite photography to get the bigger picture.

One flight the morning after a heavy frost revealed serious problems. The neighboring vineyard had run a wind machine overnight and had no frost damage, and from the road the vineyard Kunde was interested in looked green and healthy. But from the air he could tell that actually, most of the vines had been hit by the frost; the leaves were brown and shriveled.

Looking at aerial photography of an old vine Zinfandel vineyard planted 80 years ago, it's obvious that some vines are healthier and more vigorous than others. The land used to be a river valley and the richer soil from the river bed explains some of the variation, but one particularly green and leafy area turned out to be a broken irrigation line. You can spot it in seconds in the photograph but the farmer hadn't noticed the difference on the ground.

With the irrigation line fixed, you're left with a vineyard where you might want to harvest the grapes from the sparser vines separately, depending on how consistent you want the grapes to be.

In addition to looking at the images himself, Kunde is also comparing them to historic photographs of California vineyards from the Cal-Atlas project using MultiSpec software from Purdue University designed to analyze aerial and satellite images. "You can teach it what the canopy looks like and it can see quantitative difference in vegetation over time." So if a vineyard doesn't look as healthy as it used to, you could change the way you treat the vines, checking the way the irrigation and manuring is done and taking samples to check the nutrients they're getting.

Kunde calls it "farming smarter for the site" and like his temperature sensors, he expects the technology to get cheap enough for any wine maker, not just the big labels. "It's not so much 'why should I do that?' and more that 'I can do that so why wouldn't I?' Pretty soon it will be just another tool you can use."

But while some wineries are monitoring their vines because they're keen to reduce the amount they irrigate (an expensive thing in Napa) or to push vineyards to deliver more consistent fruit, Kunde is most interested in unlocking the unique flavors in the grapes. "There's a relationship between the vine and the soil; the roots, the soil type, how old the soil is the climate, the organisms in the soil, the exposure. It influences how the vine grows and the fruit it produces. It's called site expression."

So while he's keen to reduce the variability in the quality of the grapes he buys and understand how the temperatures in fermentation affect the development of flavors, he doesn't want to end up with cookie-cutter formulas for making wine.

"Wine hasn’t become a commodity; it's still tied directly to the earth. I don’t want to force the wine one way or another." Tasting his first vintages from the barrel in the cool wine cave, it seems as it site expression makes for good wine. And you can decide for yourself -- Kunde's first Arduino-monitored wines went on sale this year.

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