Robert Steinberg had a big thing for chocolate. Big enough to co-found a company — Scharffen Berger — and build it into one of the world’s best chocolate makers.

With his death Sept. 17 from lymphatic cancer, that world is now a little less sweet. The longtime San Francisco resident was 61.

Though trained as a physician, Steinberg switched careers after his 1988 cancer diagnosis. His lifelong love of fine food led him to study the art and science of chocolate. Together with his friend, former winemaker John Scharffenberger, he formed Scharffen Berger in 1996.

“He was always a truth-seeker,” said Brad Kintzer, an executive at Scharffen Berger and friend of Steinberg’s. “That’s what drew him to chocolate. He wanted to understand better the variables that influenced chocolate quality, and once he focused his energy, there were an endless number of questions. That led him to be the first person in America to make really high-quality chocolate.”

In 2004, Steinberg was the focus of a j. cover story on the Bay Area’s Jewish chocolate makers. He said at the time, “I’m very Jewish in terms of my ethnic identity. What I associate ideally with being Jewish is compassion for other people, social consciousness and intellectual curiosity.”

Born in Boston, Steinberg earned his bachelor’s degree at Harvard and then went on to the University of Connecticut for his medical degree. He moved to California to launch his medical practice, eventually settling in San Francisco.

After being diagnosed with cancer in 1994, he attended a two-week workshop at a chocolate factory in France. That experience inspired him to develop his own gourmet product. “I got interested in the science of it,” he told j. in 2004. “I got obsessed.”

At Scharffen Berger, Steinberg played several roles, but primarily served as chief buyer. He would travel the world sampling cacao beans, which the company roasts at its Berkeley headquarters.

Scharffen Berger pushes the cocoa content of its products to high levels, with its extra-dark chocolate product weighing in at 82 percent.

“The flavor was influenced by the chocolate I helped make in France,” Steinberg told j. “A fruity quality, intensity of flavor, marked by an acidity in the finish, like a good wine.”

Steinberg was proud that all Scharffen Berger products are certified kosher.

“I tasted chocolate with him every day,” Kintzer said. “He always encouraged people to taste it like you never had chocolate before, so you don’t lose out some unique factors and qualities. That applies to a lot of things in life.”

Hershey Chocolate bought Scharffen Berger in 2005, and though some worried the quality of the product might slip once it fell into the hands of a corporate giant, Steinberg and his staff made sure that did not happen.

For 20 years, Steinberg battled cancer, and though he had his share of bad days, he never lost his passion for life and his work. He had even planned to make visits to cacao bean growers in Central and South America at the time he developed a fatal fever a few weeks ago.

Besides his tenacity, “Robert, to me, was always someone who encouraged people to look at things with a beginner’s mind,” Kintzer said. “I will never forget him encouraging people.”

Steinberg is survived by his mother, Selma Goldberg of Marblehead, Mass.; sister Nancy Steinberg of New York; and stepsister Judith Margolin of Stamford, Conn. Donations can be sent to the Leukemia and Lymphoma Society, P.O. Box 4072, Pittsfield, MA 01202.