Tucked away behind a glass door in a new block of buildings on Fourth Street sits Berkeley’s only chocolate manufacturer.

Bittersweet, best known for its string of cafes in Oakland, San Francisco and Danville that serve delicious cups of hot cocoa, has started producing its own chocolate bars. Made from single-source farms or collectives in Bali and the Dominican Republic, the Bittersweet bars are made in small batches that can take up to a week to finish.

“We’re the only beans-to-bar (operation) in the East Bay,” says Penny Finnie, who owns Bittersweet with Seneca Klassen.

When Finnie, who lives in Berkeley and who was a founder of the search engine Ask Jeeves, and Klassen, a former graphic designer, dreamed up Bittersweet five years ago, they were interested in capturing the country’s growing fascination for high-quality chocolate. They stocked their cafes with artisanal chocolate bars and cocoa from around the world, and created fabulous desserts like the café’s chocolate cake with cinnamon-laced frosting.

Seneca Klassman and Penny Finnie, owners of Bittersweet

But making chocolate had always been Klassen’s true ambition and, once the business was stable, he focused his energies on turning cocoa beans into chocolate bars. It was not an easy transition; there are no “how-to” books on making chocolate and very few small-scale chocolate makers who take on apprentices, according to Klassen. Culinary schools teach confectionery classes, where one can learn what to do after chocolate is produced, but not how to make the actual substance.

Klassen learned a lot through trial and error. An uncle in Ecuador sent him a ten-pound bag of cocoa beans. Klassen tried roasting them in small batches. The results were uniformly awful.

Then, through a mutual friend, he met Alice Medrich, Berkeley’s high-profile chocolate crusader, owner of the chain of Cocolat confectionery stores, and the author of numerous cookbooks. Medrich’s brother Albert was the chocolate maker at Scharffen Berger Chocolates, and invited Klassen to come in on the night shift to watch him make the product. That was the opportunity Klassen needed: to study a master craftsman at work.

“I’m really self-trained,” says Klassen.

Now Klassen produces about 600 chocolate bars a month for the Bittersweet label. He makes a bar with 75% cocoa, one with 65% cocoa, and a milk chocolate bar.

All of the cocoa beans are from a single source so each batch tastes distinctive, said Klassen. The cocoa beans arrive already fermented and Klassen roasts about 50 pounds each week in the store in Rockridge. He takes the roasted beans to Bittersweet’s factory on Fourth Street in Berkeley, where a machine takes off the husk and crushes the nibs (watch the slideshow above to see the process in action).

Klassen then pours the nibs into a grinder encased in a steel casing. The nibs and any added ingredients, like sugar or milk, spend up to five days in the machine. It takes that long for them to reach the proper consistency. Then Klassen tempers the chocolate and pours the thick, heavy paste into molds. The entire process, from cocoa bean to finished bar, takes about a week, he said.

The manufacturing of its own bars is just one of the steps Bittersweet is taking to provide its own products. While the cafes used to sell Blue Bottle Coffee, Bittersweet is now buying and roasting its own coffee beans. Huge sack of coffee sit adjacent to cocoa beans in the warehouse.

With the recent closure of Sharffen Berger, Bittersweet is the only chocolate manufacturer in the East Bay. It’s a shame, says Klassen, because the Bay Area used to support a vibrant chocolate manufacturing community. Guittard Chocolate Company has roots back to the 19th century.  Now the growth of artisanal chocolate makers is happening more in the Mid-West than in the Bay Area, says Finnie. But the owners of Bittersweet are happy to share what they have learned.

“Everyone learns from one another,” says Finnie.

Frances Dinkelspiel, Berkeleyside and CItyside co-founder, is a journalist and author. Her first book, Towers of Gold: How One Jewish Immigrant Named Isaias Hellman Created California, published in November...