Composting in wine country: Napa Valley’s multi-decade circular economy story

Many areas in California are working to scale up composting infrastructure as part of a state mandate to dramatically reduce organic waste disposal by 2025. The Napa Valley is decades ahead, thanks to a high-value agricultural and vineyard economy.

Processing many tons of grape pomace — a residual material in the winemaking process — from vineyards in the valley was an early impetus for composting in the region. Today, while new operations have increased their activity far beyond just pomace, local participation in food scrap diversion is still relatively low, and some facilities are accepting organic waste from across the San Francisco Bay Area to fill their capacity.

Composting in wine country

One of the first ventures to develop composting infrastructure in the Napa Valley was Upper Valley Disposal & Recycling in St. Helena. Founder Bob Pestoni launched the venture in the late 1950s as an answer to the question many vineyards had of how to dispose of the many tons of grape pomace produced each harvest.

Pestoni had begun accepting food scraps several years earlier from across the Bay Area to feed the 600 hogs on his farm. In 1966, he signed his first contract with vineyard owner Robert Mondavi.

“Mr. Mondavi didn’t want to dump the residual on the ground on his property,” said Christy Pestoni, the company’s chief operating officer. “And so he called my dad.”

It didn’t take long for word of this service to reach other vineyards and for the operation to expand beyond hogs, especially because, as Pestoni recalls, “the first year my dad fed [the grape pomace] to his pigs, he mixed it in with the swill that he was already feeding them and the pigs got drunk.”

In the years to come, Upper Valley continued to invest in the science of composting, and has since been responsible for some of the earlier research to come out of California — as highlighted in a 1993 National Geographic spotlight on their operation.

Agenda for a 1991 vinicultural forum hosted by Upper Valley

Permission granted by Upper Valley Disposal & Recycling

The combination of wine and waste industry stakeholders resulted in a two-year “vinicultural forum,” including education efforts as well as compost use trials at Robert Mondavi Winery and Domaine Chandon over a three-year period. “We brought in soil scientists from the region and university experts from Italy to help educate farmers about the benefits compost use can have for soil, plant and fruit quality,” said Pestoni.

One of the earliest realizations Upper Valley made about its operations was the need to supplement compost piles, to balance out the grape pomace.

“When grape pomace is composted in a high percentage, the resulting compost is rather acidic,” explained Neil Edgar, a compost permitting consultant and executive director of the California Compost Coalition. Balancing the acidity required a source of carbon, which was found in rice hulls imported from farmers in Butte County, about 150 miles northeast.

Today, grape pomace still comprises around 60% of the Upper Valley’s feedstock, which it acquires during the wine grape harvest season from August to the beginning of November. But as residential and commercial composting has taken hold in recent years, the company no longer needs to import carbon from across California.

Pile of grape pomace at California compost facility, mountains in background

Grape pomace at the Napa Materials Diversion Facility

Karine Vann/Waste Dive

Shifting market demands

In the last several decades, composting has expanded beyond the Upper Valley. The Napa Materials Diversion Facility, owned by the city of Napa and operated by Napa Recycling & Waste Services, is an industrial recycling and composting operation built in 1993 to meet the shifting needs of the region.

Since the early days of the wine boom over half a century ago, the valley has transformed from a sparsely settled agrarian region to a tourist destination now home to hundreds of wineries, commercial kitchens and an increasingly dense population. As a result, regional infrastructure has expanded to meet more diverse needs.

Today, the NRWS facility is permitted to handle up to 500 tons per day of organics. The majority is currently processed on site using a covered aerated static pile system, with additional material getting transferred to a new composting site in Yolo County. According to Tim Dewey-Mattia, recycling and public education manager at NRWS, only 7% or 8% of the feedstock at the municipality’s facility in American Canyon consists of grape pomace. What that facility does receive is currently being sold for cattle feed as an alternative to grain, at a time when grain prices are high and the nutrient value is quite similar.

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