The decision about when to promote a minor league player is as much art as science, and it’s certainly an eye-of-the-beholder process. Literally.

“You go watch them,” Terry Ryan said, when asked to name the most important component of the transaction. “I give my opinion, but only on guys I’ve seen.”

The Twins are careful about elevating their prospects, willing to wait until they are sure each player is ready. And just what constitutes readiness?

“There’s a physical part and a mental part. It’s not just one thing,” said Ryan, the Twins general manager. “We don’t have any strict guidelines or [benchmarks]. I don’t put a timetable on any player. I don’t think that’s healthy.”

That eye-test philosophy is getting plenty of attention lately, as fans grow restless waiting for 2009 first-round pick Kyle Gibson to be summoned to Target Field. The Twins have demoted two members of their starting rotation to Class AAA Rochester in the past 10 days, but chose to wait on putting Gibson in one of those slots. Ryan, who has witnessed a couple of Gibson starts this year, insists that firsthand observation convinced him that Gibson needs more experience, and especially more consistency.

“He’s kind of dictated that. He’s been good, he’s been bad, good, bad, good,” Ryan said. “I’ve always said, ‘Go ahead, put some pressure on us.’ ”

Gibson gave up a three-run homer in the third inning of the Red Wings’ victory over Lehigh Valley on Thursday, and three more runs in the sixth inning, a mediocre start that seems to fall into his on-and-off pattern. Ryan said he understands how much fans want to see the hard-throwing righthander — but knows how quickly that can change.

“The worst thing you could do to the kid is bring him up, and he has a bad outing. The fanbase would sour on him so quick,” Ryan said. “I don’t want that to happen. When we bring him up, we want him to contribute for the better part of this season, instead of bringing him up just to showcase the guy we’ve got high hopes for.”

It’s a cautious approach that Ryan knows can frustrate players; he cites Torii Hunter, Corey Koskie and A.J. Pierzynski as previous Twins prospects who grew impatient with his willingness to leave them in the minors. But he believes extra time spent in the minors pays off with better results, and cites Aaron Hicks’ slow start as evidence.

“Most of the time, we’re right” about when to promote a player, Ryan said, “because we’re going to be conservative.”

Decisions about when to promote players within the Twins system, from the entry-level signees in extended spring training to the one-step-away veterans at Rochester, rest with Brad Steil, the organization’s director of minor leagues. The managers and staffs of each minor league team add their opinions, as well as the system’s roving instructors and the Twins front office, but Steil, who took over for Jim Rantz this year, has the final say.

Promotions to the majors, however, are Ryan’s responsibility.

“I hope [Gibson] does spin one up there, that’s what we want to see,” Ryan said. “We’re just trying to help him help the team.”