On Dec. 1, the day that the nominations were announced for the 2011 Grammy Awards, Glassnote Records founder Daniel Glass sat in a New York screening room with his family watching the new Sofia Coppola film, "Somewhere."

Phoenix, the alt-rock band that Glass transformed during the past year into an arena-filling act, composed the score for "Somewhere"-and seeing the movie brought Glass full circle on the group's accomplishments. Twelve months earlier, he was anticipating Phoenix receiving a Grammy nomination. (It did, and went on to win the award for best alternative music album for "Wolfgang Amadeus Phoenix.")

Mumford Best New Artist Hub | Grammys 2011 Main

This year, Glass is bestowing his kingmaker skills on another up-and-coming band-this time around, he sat in the screening room waiting for word on a Grammy nod for British folk rock four-piece Mumford & Sons.

"After the movie, we went home and were watching the nominations on TV," recalls Glass, a trim man in his early 50s with a taste for posh jeans and expensive sweaters. "First they showed footage of the band, then they said 'best new artist' and we just started screaming." The band received two nominations, including one for best rock song ("Little Lion Man"). Glass spent the rest of the night on the phone.

The following day was a blur, and not just because the Mumfords (as Glass and company fondly refer to them) sent champagne to the office; the label head was bombarded with congratulations from industry friends and cohorts. In an era when grass-roots artist development seems as rare as seven-figure first-week album sales, Glass had taken a collection of beardy, roots music-worshipping, photo-and-journalist-averse kids and turned them into that rarest of commodities-a critically adored, commercially successful rock band whose singles compete with Rihanna's for chart space.

"People were saying this was a vote for authenticity," Glass says. "It's really been a great few days, especially considering the last taste of this chapter was the Terminal 5 shows [in New York], which were so spectacular."

The two sold-out concerts capped the Mumfords' second American tour this year, a five-week stint that saw them jump from the small theaters they were playing a few months ago to 3,000-plus-capacity spaces. Ten months after its release, the band's debut, "Sigh No More," was certified gold by the RIAA. It's now up to 588,000 units sold, according to Nielsen SoundScan, reaching as high as No. 16 on the Billboard 200. "Little Lion Man" topped Billboard's Alternative chart and peaked at No. 2 on the Triple A tally.

But those are just the numbers. All one really needs to know about the Mumford phenomenon can be seen on the faces of the fans crammed shoulder to shoulder at shows, mouths open, singing along to every word of every song. Or, as Glass puts it, "like Christmas and Thanksgiving all in one. It just gets warmer. It just gets bigger."