MUKILTEO — Brian Sollenberger, one of two co-founders of Mukilteo’s successful Diamond Knot brewery, died in an apparent accident at his home early Saturday. He was 46.

Sollenberger may have slipped on the stairs leading to the front door of his Mukilteo home and fell, possibly hitting his head on a rock, said Bob Maphet, the brewery’s other co-founder.

No one was with him at the time of the accident, so it’s not known exactly what happened, Maphet said.

Sollenberger had been working alone Friday night at the Diamond Knot brewery on Chennault Beach Road, Maphet said.

One of Sollenberger’s three sons had woken up to go to the bathroom and saw his father’s car pull into the driveway about midnight, Maphet said. Seeing or hearing nothing unusual, he went back to bed.

Sollenberger’s wife, Ann, woke up at 5 a.m. and found her husband at the bottom of the front steps, Maphet said. Medics were called.

“When they got there they tried everything to detect any kind of a heartbeat and he was gone,” Maphet said.

One of the paramedics, who knew Sollenberger, said he died of a head injury, Maphet said. “He said he went quick,” he said.

The Diamond Knot brewery celebrated its 15th anniversary just last month. When Sollenberger and Maphet, 50, met in the beer-and-wine club at Boeing in 1993, Sollenberger already had the concept for a brewery in mind.

The two collaborated, starting by leasing 300 square feet from the Cheers Too pub on the Mukilteo waterfront in 1994. In 1999, they bought out Cheers Too, Maphet said, and established what is still the Diamond Knot Brewery and Alehouse.

The business opened the larger-scale production brewery on Chennault Beach Road in 2005, a restaurant-pub on Camano Island in 2007 and took over the former Riley’s Pizza in Mukilteo last year. Diamond Knot now employs 65 people.

Sollenberger, who continued to work as an engineer at Boeing even after the brewery attained success, was the technical brains behind the business, his partners said.

“He was incredibly knowledgeable about brewing,” head brewer Pat Ringe said.

“He was always challenging what we thought was conventional wisdom. He was really, really meticulous. He overengineered to the point of being bombproof.”

For example, Sollenberger designed and personally built a keg washer, Ringe said.

“Brian took it on himself to build a pretty technologically marvelous piece of machinery, kind of a semiautomatic affair,” he said. “He started with a giant shallow sink, or basin, and built the entire mechanism around it.”

It took a year-and-a-half of working nights and weekends, “but when he delivered, it was over the top.”

If he didn’t know the answer to a technological question, “he would do copious amounts of research,” Ringe said.

In the early years of the brewery, Sollenberger also handled the social end, circulating at the alehouse and talking up the product, Maphet said.

“He was a very social person, very outgoing,” he said. “He didn’t like to be alone, he liked to be around people and talking.”

Sollenberger also was active in the community, sponsoring an annual luau for the Mukilteo Boys &Girls Club and attending meetings of Save Our Communities, the group that opposes commercial air service at Paine Field.

Ringe said Sollenberger was very supportive of his employees.

“He was just a really big-hearted guy,” Ringe said. “He really, really cared about everyone’s happiness and well-being here in our little family.”

Ringe said Sollenberger’s expertise is irreplaceable.

“Hopefully I’ve learned enough from him along the way that I can keep things together,” he said. “It’s only been a few days, but I feel like I’m standing at the edge of a large hole I have to step into.”

A native of Illinois, Sollenberger is survived by his wife, Ann; sons Seth, 15, Eric, 11, and Will, 9; and his parents, Alice “Pauline” Meyer and Terry Sollenberger.

Bill Sheets: 425-339-3439; sheets@heraldnet.com.