Burchett, 46, is leaving to take a study break at Kingston University, where she is enrolled on a writing course.
"We're separating on perfectly good terms," she said.
"I had a great time at Castel and it was my decision to go and do something else.
"I'm going to do something I've been looking forward to for years without ever thinking I would do it.
"I absolutely adore the wine business and will be trying to keep my hand in, but for the next year the priority is on the writing."
Burchett leaves today (June 13). Castel has not yet named her successor.