Do you know what zero zero wines are?

You’ll likely find “zero-zero wines” in a wine shop. The description is the latest marketing phraseology for a subset of natural wines. It means there are zero added yeasts and zero added sulfur, a minimalist approach to winemaking that’s attracting both fans and critics.

Winemakers of zero-zero wines do not augment their crushed grapes with commercial yeasts. Instead, they rely on the naturally occurring yeasts on the grapes and in the cellar to ferment their fruit. While these ambient yeasts are harder to control, natural winemakers argue they imbue a wine with more complexity and nuance.

After fermentation, these winemakers also forgo adding sulfur, even though the antibacterial can prevent wine from turning into vinegar.

Sebastopol vintner Martha Stoumen has one foot in the zero-zero camp and one foot out.

“Over the years we have crafted some (zero-zero) wines. However, I don’t strictly make these kinds of wines,” she said. “Sulphur dioxide is a naturally occurring preservative that can help prevent unwanted microbes and bacteria from taking over at any stage of a wine’s life and reduce oxidation. During the aging process, I might choose to add small amounts of sulfur (less than 25 parts per barrel) to specific barrels in order to support healthy aging. We always list any sulfur additions on our website.”

Stoumen, however, is completely aligned with the zero-yeast part of the equation.

“Instead of using a single commercial yeast species, we embrace native fermentations and the many flavors a diversity of microbes bring to our wines,” she said. “Once the primary fermentation is complete, the saccharomyces cerevisiae (ambient yeast in the cellar) kick in to finish off our fermentations. These yeasts offer a distinct thumbprint on the wine, contributing to a larger sense of the place and season.”

Stoumen said complexity and nuance are her end goals when producing an agricultural product. Consistency is not.

She said while consumers may be at odds over zero-zero wines, the broader category of natural winemaking is popular with her generation — millennials.

“I think that it mostly stems from caring about Earth-first practices and being conscious of what we consume,” Stoumen said. “The way I see it, the natural wine movement is not an isolated campaign led by rogue winemakers, counterculture somms and stylish consumers — although it does sound very sexy that way. But I see it as a natural progression within a larger movement towards greater transparency and environmental responsibility in what we consume.”

The winemaker said those who have opted for grass-fed beef, fair-trade coffee, cage-free eggs or craft beer are already part of the natural wine movement.

Stoumen, who grew up in Sebastopol, traveled to Tuscany to live and work at Tenuta di Spannocchia, an organic polyculture farm and learning center. She was put to work pruning vines and harvesting grapes.

“Making wine was a blast,” she said. “Jumping in enormous vats of grapes? Yes, please. Since I don’t come from a winemaking family, I knew that in order to keep exploring my interest, I would have to find my mentors through internships.”

Stoumen spent the next eight years, from 2006 to 2013, interning and apprenticing with winemakers around the world — in Italy, Germany, France and New Zealand — earning her master’s degree in viticulture and enology at UC Davis in 2012 after studying for two years between harvests.

“While I lean heavily on my science background in the cellar, there's no substitution for experience in the wine industry,” she said. “Each of my winemaking mentors shared a love of their land and tradition that inspired me to return to California to explore the question: What does California taste like? More than anything, I wanted to approach this question with the same reverence my mentors had for their craft and soils.”

Stoumen came back to California in 2014, founded her winery and sought out growers who were committed to organic farming, soil health and vine longevity.

“I knew I wanted to make wine without taking shortcuts, even if it wasn’t the easy or cool way at the time,” she said. “I wasn't ready to give up on any of these values, so it became clear that I needed to start my own label and take part in bringing California winemaking back to its roots.”

Stoumen crafts about two dozen wines each year and has a couple of zero-zero wines in her lineup — the Piquettes, 2021 12 pack, $120; and the Vermentino, 2021 Mendocino County, $38. marthastoumen.com

Here are a handful of other zero-zero wines to explore:

Caleb Leisure Wines: Zeugma, 2019 Syrah (95% syrah, 5% viognier), Sierra Foothills, $35. calebleisurewines.com

Coturri, 2020 Albarello Red (50% carignan, 25% zinfandel, 25% petite sirah), $35. coturriwinery.com

AmByth, 2019 Sangiovese, Paso Robles, Mark’s Vineyard, $45. ambythestate.com

Ashanta, 2020 Old Vine Carignan, Testa Vineyard, Mendocino, $32. ashantawines.com

Wine writer Peg Melnik can be reached at peg.melnik@pressdemocrat.com or 707-521-5310.