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Wine Disasters

Mystery on The Bottling Line

Everything was done properly. So what caused the fizzing — and loss of precious wine?

Jeff Siegel By September 23, 2021
illustration of man looking at wine bottles through magnifying glass
Illustration by Kevin Fales

Two weeks after David Vergari bottled his wines, funny things started happening. Wines that weren’t supposed to be fizzy had fizz in them. Some of the tops wouldn’t stay down. And there was a decidedly off odor when he took the tops off to investigate.

“When something happens to a wine after it’s gone into the bottle, well, that’s another thing altogether,” says Vergari, who was then making wine for a small California producer but has since made wine throughout the state and for his own label. “You usually have a major problem whose impact extends far and wide, affecting the sales and marketing folks, distributor relations, and your own job security — just to name a few.”

In other words, fizzy wasn’t a bonus. Fizzy was a sign of serious problems, of what’s called re-fermentation in the bottle — a problem so severe it could mean the future of the winery. In this case, it was not only 3,000 cases of the winery’s products; the winery was making wine on behalf of another producer, and their wines were fizzing too. Hundreds of cases of them.

Double jeopardy. Vergari had to find out what happened, why it happened, and fast.

The process turned out to be as much detective story as winemaking exercise, and Vergari had to keep Sherlock Holmes’ axiom in mind: “Once you’ve eliminated the impossible, whatever remains, no matter how improbable, must be the truth.”

The mystery yeast

The re-fermentation was confined to white wines that were either off-dry or sweet, while all the reds and the dry whites were fine. Vergari sent samples of the fizzy wines to a commercial laboratory, whose library included more than 100 different yeast strains. The result, said the lab’s director, was baffling. Yes, they had identified a yeast strain in the faulty wines, but one the director had never, ever seen before.

The wines had been sterile bottled; that is, the fermented grape juice had been poured through a 0.45-micron membrane into the bottle. Think of that as a filter, where the 0.45-micron opening is so small that it can just barely be seen by the human eye. “That kind of membrane is supposed to stop any microorganism from contaminating the wine,” says Vergari. “And when I checked the integrity of the membranes, they were sound.”

Vergari had used a mobile bottling line, so he next called the winemaker who had used the line before him, who, as it turned out, had also sterile bottled and had had the exact same thing happen.

Vergari played a hunch. “What kind of bottles did you use?” he asked. “The owner got a special deal on some foreign glass,” said the winemaker. “I really don’t know where the bottles came from.”

A solution was coming into focus. Vergari told the winemaker to send him samples of the bottles of their faulty wine.

Mystery solved?

The other winery’s samples were sent to the same lab. The results didn’t surprise Vergari, though the lab director was still baffled. The same yeast was in the other winery’s wines, too. How did an unknown yeast show up where it shouldn’t have?

Vergari pounced. “That’s because it doesn’t come from this continent,” he said. 

Now, the puzzle began to seem a lot less puzzling. Almost certainly, the yeast on the bottles had sent huge amounts of the alien yeast into the clean room where the bottling took place, where the mystery bottles were stored. 

When the mobile bottling line arrived, the yeast then floated down and settled on the filler spouts. The next day, when the line arrived at Vergari’s winery, the filler spouts were contaminated with the new yeast and the spouts inoculated the wine with the yeast when the bottles were filled. Yeast being yeast, it began to feed on the residual sugar in the sweeter wines. Soon, re-fermentation was underway.

The epilogue

Despite the mystery being solved, the winery still faced a devastating financial loss. Vergari disposed of the contaminated wines, selling most of it for industrial alcohol; in that case, it didn’t matter that the wine had re-fermented. As long as it had alcohol, that was enough.

Then there was a meeting with the owner of the mobile bottling line to arrange a settlement, who, says Vergari, was adamant that it was not his fault.

Vergari laid out the story: The mystery yeast. The mystery bottles. The yeast in the first winery’s wine. The failure to make sure the bottling line was sanitary when it came to Vergari’s winery.

“We immediately arrived at a satisfactory settlement,” says Vergari. 

Elementary, my dear Watson.