You can take the budget guru out of Washington, but you can’t take Washington out of the budget guru.

In his 13 days as GOP vice presidential nominee, House Budget Committee Chairman Paul Ryan (R-Wis.) has taken care on the campaign trail not to reveal too much of his inner policy wonk, opting in his stump speeches to use soaring language about “the American idea” and to take jabs at President Obama rather than to get into the nitty-gritty of budget details.

But in an hour and a half of closed-door discussions Thursday with campaign aides in Boston and on the trail in Springfield, Mo., Ryan couldn’t help but focus in on one of his favorite topics: the federal budget.

In this case, it was a new Congressional Budget Office report released this week regarding the looming fiscal cliff.

“I wanted to get into the CBO baseline; that’s kind of the thing I like to look into — and a new deep dive on the energy stuff,” Ryan told reporters Thursday night in his second impromptu visit to the back of his campaign plane this week.

The “energy stuff” was a reference to a newly unveiled proposal by his running mate, presumptive GOP nominee Mitt Romney, who focused on energy at a campaign event in New Mexico on Thursday.

Ryan — the architect of the House GOP budget blueprint and a seven-term lawmaker known for delivering detailed PowerPoint presentations at town halls in his Janesville, Wis.-based district — has largely steered clear of talking about the specifics of budget reform on the White House trail for fear of confounding voters with talk of Washington’s Byzantine budget process.

But that doesn’t mean Ryan has entirely managed to avoid delving into budgetary minutiae during his brief tenure as vice-presidential nominee. At a campaign stop at a Raleigh sheet metal company on Wednesday, he let slip a mention of “FICA” — the Federal Insurance Contributions Act.

And at a northeast Ohio hot dog restaurant last week, he fielded a Medicare question from a reporter by bringing up the “B” word — “baseline,” a bit of Washington-ese that Ryan at the time acknowledged is “a little bit wonky.”

Ryan’s unannounced trip to the back of his campaign plane Thursday night came as the presumptive GOP vice presidential nominee has yet to formally take questions from his traveling press corps in his nearly two weeks on the trail.

At each campaign stop, Ryan has sat down for multiple local television interviews and has done national TV sit-downs with Fox News Channel and CNBC.

On Thursday afternoon, at a defense roundtable in Fayetteville, N.C., it briefly appeared that Ryan might take questions from reporters before a campaign aide quickly tamped down on the idea.

Ryan instead has thus far sought to woo his traveling press corps through more informal means, making friendly conversation on his campaign plane and taking questions for only a few minutes before retreating to his seat.

On Wednesday, he brought reporters a tray full of cookies and fielded several questions on the Todd Akin controversy.

The next night, after a Missouri fundraiser that netted $1.2 million, Ryan stopped by the back of the plane to say farewell to a departing Fox News Channel reporter — and took a few moments to respond at length to a query on welfare reform.

Leaving his suit jacket and tie at his seat shortly after takeoff, Ryan was accompanied by two aides as he ventured to the rear of the darkened aircraft. He greeted the dozen or so members of his traveling press corps, who scrambled to grab their pens, notebooks, voice recorders and video cameras as the candidate approached.

“You’re leaving, I heard,” Ryan, clad in a white shirt and dark pants, said to the Fox News reporter, who next month will shift over to cover Ryan’s vice-presidential rival, Joe Biden. “Sorry about that. ... Are you going over to Joe’s?”

“Yeah,” the reporter responded, then asked after a few moments of chit-chat: “Do you have a message for me to bring to Joe?”

“Say hi,” Ryan said. “Go Packers.”

One reporter asked Ryan about a local TV interview during which he was asked a series of questions in lightning-round style and was pressed about his affinity for health food.

“I love asparagus,” Ryan explained. “It’s my favorite vegetable. I’m eating it right now. Or, I’m going to eat it in a minute.”

“They just put it down for you, boss,” an aide said.

“Oh, did they?” asked Ryan. “I really like asparagus.”

Asked by another reporter about his comments on welfare reform at the Missouri fundraiser — during which the presumptive GOP vice-presidential nominee had renewed a Republican critique of Obama that has been discredited by independent fact checkers — Ryan gave a lengthy defense of his remarks.

“Read the law,” he said. “The law does not reinstate the ability to waive the work requirements. When we passed the reauthorization of welfare reform, we tightened the work requirements to make sure it was actually getting people to work. And so, I believe the law does not allow that kind of flexibility, and that it undermines the spirit of welfare reform, which was to transition people from welfare to work.”

He fielded two more questions — on his policy discussions and on his differences with Romney on abortion — before telling reporters that he hadn’t meant to “get into a press conference.”

“I just wanted to come back and say bye; nice to see you. I didn’t mean to get into all these issues,” Ryan said.

With that, he headed back up to the front of the plane. And his traveling press corps was left to such time-honored tactics as they’d employed earlier in the day, when one reporter took a Sharpie and wrote a message for Ryan on an orange.

“Hey Congressman, thanks for the visit. Don’t be a stranger,” read the note on the orange, which the reporter sent rolling up the aisle to the front of the plane near where Ryan was seated.

A few minutes later, the orange rolled back down the aisle bearing a new message signed not by Ryan, but by his traveling press secretary:

“Eat your fruits and veggies if you want more cookies.”