“Expansion is continuous” for Gourmet Mushrooms Inc., Sebastopol, Calif., said Bob Engel, chef liaison.

The company, which just celebrated its 35th anniversary, is learning how to get more out of its growing facility.

At one time, it was thought the firm might top out at 14,000 pounds per week, but that figure is now up to 20,000 pounds, and the company expects to produce 25,000 pounds per week by fall.

“The growth in the specialty end of mushrooms is really quite extraordinary,” Engel said.

“Year-over-year growth for us is running about 20%.”

Gourmet Mushrooms has achieved that growth because the company produces an extensive selection of mushrooms that you’re not likely to find elsewhere, Engel said.

The company even trademarks it varietal names.

“It kind of adds to confusion a little bit, but it also helps differentiate ourselves in the marketplace,” he said.

Gourmet Mushrooms is relatively small but “very interested in staying in the forefront of things,” Engel said.

“The easiest way for us to do that is to compete largely on the basis of quality and variety.”

The company’s newest addition is the Nebrodini Bianco — a large, white oyster variety that’s shaped similar to a calla lily.

It’s a tasty variety and good to grill, so it sells well during the summer months, Engel said.

The company also has increased its production of maitakes.

“Other people do grow that, but there’s a wide range of qualities, styles and types out there,” he said.

“We’re really happy with the one that we grow as far as flavor and aroma are concerned.”

Gourmet Mushrooms is bringing out a new pack within the next couple of months called the specialty trio.

Originally developed for Costco in a 1-pound size, it will contain the company’s Velvet Pioppini, Forest Nameko and Nebrodini Bianco or Alba Clamshell varieties in an 8-ounce package.

The firm’s current retail best seller is the chef sampler — an 8-ounce pack that typically contains the Trumpet Royale, the Alba Clamshell, the Brown Clamshell and the Velvet Pioppini.

Engel said the company’s mushrooms are not grown in manure but on a kind of substrate that is primarily wood.

“Those mushrooms, which are sometimes referred to as forest mushrooms, have always been the type that we grow,” Engel said.