(NYTimes) - When you buy a bottle of Napa Valley cabernet sauvignon, you trust that the bottle is filled with wine actually made from cabernet sauvignon grapes that were grown in the heart of California’s wine country.

The strange tale of Jeffry James Hill might make you question that faith.

Mr. Hill, 36, was a longtime Napa vineyard manager who worked his way up from agricultural pest control to stake a claim as a maker of $100 wines.

In 2012, he set himself up beside some of the most prestigious names in the business when he leased a winery along Napa’s Silverado Trail, a destination for wine aficionados from around the world.

A beefy man with the bearing of someone accustomed to working the land, he could hold a busload of tourists spellbound with homespun stories of a vintner’s life. Mr. Hill also had a knack for marketing, getting Hill Wine Company bottles on the United Airlines planes shuttling American athletes to the Winter Olympics in Sochi, Russia.

At the same time, he continued to work in the less glamorous side of the industry, buying and selling grapes and bulk wine and managing fields for big wineries and small growers. His commercial clients included famous names like Don Sebastiani & Sons, Del Dotto Vineyards and Trinitas Cellars.

It was all built on quicksand. The fancy winery was more than Mr. Hill could afford, and the expenses of operating the business quickly outpaced his income. He was soon deeply in debt and resorting to deceptions like substituting cheaper merlot and malbec grapes for the much more expensive Napa cabernet sauvignon advertised on the wine labels, according to court documents. Prosecutors say he even engaged in outright theft.

Mr. Hill worked in an industry built on romance, expensive land, hard labor and a whole lot of faith, and the accusations against him have shaken the wine-growing region.

“The system is only as good as how trustworthy people are,” said Ned Hill, who is not related to Jeff Hill, and who farms for several major wineries in Sonoma County through his company La Prenda Vineyards Management.

The federal government forced Mr. Hill to cede control of his business on April 23, and Napa County prosecutors have charged him with two felonies, saying that on two occasions in October 2013 he stole grapes that his crew was harvesting for another winemaker and diverted them to his own winery.

This month, he pleaded not guilty to the criminal charges, and a trial is set to begin April 13. If convicted, he faces up to four years and eight months in prison.

Hill Wine has filed for bankruptcy and owes more than $8 million to creditors.

Mr. Hill and his lawyer declined to discuss any of the claims. But in a brief exchange in the courtroom hallway just before his plea, Mr. Hill said, “The truth will out.”

The Napa Mystique

Napa cabernet sauvignon grapes are among the most valuable in the United States. A well-made cabernet from Lake County, which abuts Napa to the north, typically sells for $25 to $30 a bottle, while a bottle of Napa cab of equivalent quality often fetches $100 or more.

That price is based more on consumers’ belief in the superiority of the region’s grapes than in the inherent quality of the liquid in the bottle.

Emmanuel Kemiji, who owns Miura Vineyards in Novato, is a master sommelier, a level of wine expertise so difficult to achieve that only 220 people in the world hold the title. In an interview, he said that even top tasters like himself would find it nearly impossible to discern the true geographic origin of a well-made cabernet.

“You line up cabernets from Napa and good-quality cabernet from Sonoma and Lake County, and it’s really tough to say where they are from,” Mr. Kemiji said. “A lot of guys would be embarrassed.” (He later tasted Hill’s top-end cabernet and found it green and underripe, but not unusual for the 2011 Napa vintage.)

While outright wine fraud is rare, many bottles on wine-store shelves aren’t what they seem because of loopholes in American wine labeling laws, Mr. Kemiji said.

Legally, a bottle that says Napa Valley cabernet sauvignon must contain 75 percent wine from Napa cabernet grapes. A further 10 percent must come from Napa, but can be a cheaper grape varietal like syrah or zinfandel. And the remaining 15 percent can be red wine from anywhere else in the state, like Fresno, where cabernet commands one-tenth the price it does in Napa.