(Originally published on Mother Nature Network)

During my two-year stint as a vegan in college, I often joked that while 90 percent of dining hall food was off-limits, at least I could always find a drink. (Clearly, I had never heard of the bacon martini.) But on a recent vacation to America’s wine capitol, Napa Valley, I stumbled upon an unappetizing fact: All along, I just might have been drinking fish guts.*

“It comes from the bladder of a sturgeon,” said Peter Hoffmann. We were standing in a newly built shed in his fig tree-adorned backyard, sampling wines from his organic and biodynamic label, Aum Cellars — straight from the barrel. Needless to say, I felt pretty cool about that. In between swirls and sips, Hoffmann explained fining — the process of introducing a tiny amount of protein into wine to attract any loose particles (tiny bits of grape skin or stems, naturally occurring yeasts, etc.) and help them settle to the bottom of the barrel. Fining, he said, helps to smooth out a wine, ultimately giving it a silkier, more consistent mouth feel. “It’s the equivalent of driving a Mercedes instead of a pickup truck,” Hoffmann said.

Despite the benefits of fining with traditional agents like isinglass (sturgeon bladder aka “fish guts”), egg white albumen, gelatin or casein (a milk protein), vegan purists say it renders the wine unfit to drink. Meanwhile, some winemakers — both vegan and not — believe that fining can remove too much sediment, taking the wine’s complexity and key flavors with it. In response to the growing market for animal-free vino, some wineries have started to specialize in vegan-friendly wines that either skip the fining process or substitute the traditional agents with a natural clay called bentonite, or with diatomaceous earth, which is sourced from hard-shelled fossilized algae.

“Hoffmann said that Europe — particularly France — has warmed up to the idea of animal-free wine since 1997 when, during the height of the mad cow disease scare, the European Union banned the practice of fining wines with dried bull’s blood. In the United States, wineries and consumers have been less eager to embrace the trend (though the use of animal blood is also banned in American winemaking). As a result, the number of intentionally vegan wineries remains in the significant minority.”

Terry Hall, communications director for the Napa Valley Vintners, said that while Napa wineries are generally known for their dynamic and cutting-edge sustainability practices, he could not name one of their 350 partner vineyards that touts its wine as vegan. Still, he said many wineries avoid fining with egg whites or other animal-based agents simply because they are expensive. Often, he said, their wines may be vegan-friendly by default, even if they do not market their products that way.

As a biodynamic winemaker, Hoffmann said he relies largely on moon cycles to help filter and clarify his wines. While he does use trace amounts of organic eggs in fining Aum Cellars’ white wines, he said, “[for the reds] I go with pure gravity and the apogee and perigee cycle of the moon [the distance the moon is from the sun at a given point during the month]. That way I’m not robbing the wine of anything it has to offer [by fining.]” A former vegan himself, Hoffmann also indicates on the label that his red wines are made without animal byproducts.

Before my visit to Napa, I always assumed that the “vegan” stamp I occasionally saw on wine bottles was one of those meaningless descriptors that marketing teams use to improve a product’s appeal within a particularly dietary zeitgeist — like stamping “fat free” on a package of baby carrots. Now that I am armed with wine’s deep, dark fishy secret, the phrase “drink responsibly” has taken on a whole new meaning.

3 vegan wines to try

Aum Cellars: Hoffmann uses small amounts of organic egg in fining their delicious white wines, but the reds are completely vegan and also organic and biodynamic to boot.
St. Helena Cabernet ($37)

Girasole Vineyards: Located two hours north from San Francisco in Mendocino, Girasole grapes are organically grown and processed using sustainable, animal-free processes.
Girasole Vineyards Pinot Noir ($16)
Girasole Vineyards Chardonnay ($13)

Frey Vineyards: Another Mendocino beauty, Frey Vineyards, claims to be the first biodynamic vineyard in the U.S.
Organic Merlot ($27)
Organic Petite Sirah ($13.50)

Find other vegan-friendly wines at the Barnivore website.

*There is debate online over whether all kosher wine is vegan. According to the 1999 cookbook Vegan in Volume, whose authors consulted with the OU, Star-K, and Kof K certifying agencies, gelatin and isinglass are not used in kosher wines, but egg whites (which are parve) are occasionally used for fining.