MORE THAN a quarter million wine lovers visit Chateau Ste. Michelle in Woodinville, Wash., each year.

Quite a few of them take the free tour of the winery, one of the best-known in the country as well as the oldest and largest in Washington state. Some take the tour to learn a little bit about wine production, grape growing and the history of winemaking in Washington, while others do so for the free wine.

The tour is one of the most important features at Chateau Ste. Michelle, according to Joan Fennell, who is in charge of training new tasting-room hires, aka guest services representatives. A former high-school English teacher, she has worked part time at the chateau for over 16 years and is clearly passionate about the place and position.

Ms. Fennell is both admired and feared by her co-workers—admired for her dedication to the chateau and feared for the high standards she holds for her charges. Ms. Fennell has taken guest services reps off tour duty for “not knowing what they’re talking about, talking too fast or not interacting with guests,” she said.