The Twins optioned Castillo to Triple-A St. Paul on Wednesday.

Just three days after he was added to the Twins' 40-man roster and 28-man active roster, Castillo will head back to the minors to open up a spot for right-hander Louie Varland, who was recalled ahead of an expected bulk-relief appearance Wednesday versus the Rays. During his brief time with the Twins, Castillo made one appearance and struck out a batter in a scoreless inning.