Deborah Voigt probably feels like throwing her scales at the next person who asks about her dismissal from the Royal Opera’s 2004 production of Strauss’s Ariadne auf Naxos, when her then-substantial size was incompatible with the little black dress stipulated for the title character.

Three years after her gastric bypass surgery that same year and more than 100lb (45kg) lighter, the 47-year-old American soprano is in her Manhattan apartment in what she laughingly calls her “down-home diva look”, good-naturedly deflecting questions about the latest reincarnation of the now notorious incident and discussing her recent success in the Lyric Opera of Chicago’s Salome. British audiences will hear her sing the riveting final scene at the Edinburgh Festival on August 30 and the BBC Proms on September 1.

During the Covent Garden fiasco it seemed as if no little black dress had garnered so much attention since Breakfast at Tiffany’s. But it was back in the spotlight in April when Antonio Pappano, the Royal Opera’s music director, responded curtly to questions at a press conference after announcing that Voigt will sing Ariadne in June 2008 – in the same production from which she was dismissed in 2004.

“I can only assume that Pappano was caught off guard,” Voigt says diplomatically. “Who knows what can come out of your mouth in the heat of the moment?”

What hurtled out of Pappano’s mouth were accusations that Voigt’s claims she was fired because of her weight were “a bunch of rubbish” and that she was “very naughty to make a big thing about something we had not announced”.

Voigt sighs: “It was a big story and it resonated with different people for a lot of different reasons. But I kind of wish it would go away as I feel like I don’t have anything more to say about it. Both sides have different ideas about what happened, but at this point I’m just happy to be going back.” She adds that working with Pappano on her 2000 recording of Wagner arias was mostly “great”.

Voigt has always asserted that her bypass surgery was unrelated to the Covent Garden shenanigans and that she simply wanted to feel healthier. She has also noted the double standard in the operatic world given the number of tubby male singers on stage. “But you can’t go around with a chip on your shoulder,” she says, regarding the pressure on singers to be thin. “That’s the way things are going and you have to deal with it.”

In any event it’s certainly been a memorable year for Voigt. A noted Strauss and Wagner interpreter, her performances as Salome in Chicago won glowing reviews.

While she didn’t do a Full Monty Dance-of-the-Seven-Veils (she appeared in a flesh-toned body suit), her slimmed-down figure allowed her to follow Francesca Zambello’s challenging direction, and her huge, lustrous soprano more than encompassed the vocal demands. “I’ve never worked so hard physically for anything and I have the bruises to prove it!” exclaims Voigt, recalling the rehearsals in Chicago with Zambello. “I was probably the most pleased with my performances in Salome as anything. It’s not something I thought I would ever sing on stage. She is such a great character, going from this naive, girlish, petulant sex kitten to basically a monster at the end of the piece.”

Judging by the reviews, it’s a challenge she met triumphantly. In The New York Times Anthony Tommasini wrote: “Her portrayal touched greatness during the gruelling final scene . . . Ms Voigt writhed with intensity, dispatching gleaming streams of Straussian vocal lines and tossing off high notes that sliced through the sumptuous orchestra.” Her performances as Helen of Troy in Strauss’s Die Ägyptische Helena at the Metropolitan Opera were also enthusiastically received.

There was initially speculation about whether Voigt’s voice would slim down along with her figure, but it certainly didn’t seem that way at a performance of Strauss’s Orchestral Songs with the New York Philharmonic last month. She admits that her weight loss has come with concerns. “I spent a long time in a really large body and singing in a particular way. I feel that because I’m not that large any more that I must work harder. So it’s difficult sometimes for me to relax and realise that I’m still the same core, strong person.”

She will need that strength for challenging upcoming roles such as Isolde, which she will sing at the Metropolitan Opera next spring. In 2011 she will brave the final frontier: Brünnhilde in the Met’s Ringcycle. “I haven’t really gone to Valhalla in terms of the Wagner. I knew Salome would work, but Brünnhilde I’m not so sure,” she says candidly.“I’m very wary of Brünnhilde. It’s a daunting event! But it’s time to put on the big girl’s outfit, as it were,” she laughs.

Fanatical opera fans tend to get protective about just which divas take on the big Wagner heroines. And some of the particularly ferocious online community haven’t always warmed to Voigt's vocalising. Of one cutting blog she says: “It was as though I had personally done something to this individual. But it’s probably ‘I don’t like Deborah Voigt because she reminds me of my wicked stepmother,’ something completely unsinger related! Whatever,” she says with a weary shrug.

But for every spiteful critic, Voigt has plenty of die-hard fans, although she is more nervous when she sings in Vienna. “It’s a very discerning public. You can’t walk in there and sing the Marschallin [in Strauss’s Rosenkavalier] and not expect that the bar is going to be set high.”

But in any circumstances, she adds, a singer’s voice can vary significantly from night to night. “We are not machines. That is what makes the experience of hearing us in performance so thrilling. Anything can happen, and sometimes it does – we can’t pump it out the same way every night. How your boyfriend treated you last night is going to affect how you sound today.”

Which leads me neatly on: does the newly svelte Voigt have a boyfriend? She admits she is “seeing someone I’m interested in. But meeting people is difficult for anybody in any walk of life,” she says. “Throw in the fact that you travel for nine months of the year and that when people meet you they think, ‘Well, that’s Deborah Voigt!’ I can sit and make eyes at a cellist in the orchestra for a week,” she says bursting into laughter, “and he’s still not going to come up and say hello!”

Deborah Voigt sings the final scene from Salome at the Usher Hall, Edinburgh (www.eif.co.uk 0131-228 1155), Aug 30. She also sings at the Proms (www.bbc.co.uk/proms 020-7589 8212), Sept 1