‘Germany’s greatest artistic asset, its music, is in danger,’ warned The Spectator in June 1937. Reporting from the leading new-music festival in Darmstadt, the correspondent mentioned only one première of the two dozen on offer: ‘The most important achievement was the scenic cantata Carmina Burana by Carl Orff, a piece that would have been impossible without the influence of the “cultural Bolshevik” Stravinsky.’

He’s not wrong: give Stravinsky’s Les Noces some nail clippers and a face scrub and you get Orff. Carmina Burana can today seem irredeemably boorish and kitsch. But you can see how the piece’s hiccupy primitivism might have once startled. Still no less startling today is Orff’s final work De Temporum Fine Comoedia (1971/1981), about the end of time, which I heard last month in Salzburg, and sounds as if it was written by a five-year-old – albeit one more into the early church fathers than Peppa Pig.

The work is the apotheosis of Orff’s postwar impulse to boil down his musical language to almost nothing: an apocalyptic minimalism of morse-code rhythms, monophonies, tremolos, scales and shrieking. A monstrous simplicity reigns: the vast army of musicians tracing out play-school shapes and melodies, often in bullying unison, while the vast army of singers shout, scream, babble and wail Becketty gobbets (‘We/ fall, fall,/ fall, fall,/ fall, fall,/ fall, fall,/ fall out of time,/ at the end of all time’). Orchestral colours, doggedly primary, are delivered in blocks, within which Orff hides more than 100 different percussion instruments from around the world (though you wouldn’t know it).

The effect is kind of horrible. And yet a part of me was glad to live in a world where a disturbed child – trapped in the body of a 75-year-old Bavarian – was given the chance to express their eschatalogical ideas in the medium of the opera-oratorio.

The audience loved it. The additional draw of this production, which opened the Salzburg Festival – the only place where this work has ever been staged before; this was its third outing – was the involvement of Teodor Currentzis, a wildly inventive conductor who really deserves the title maestro, and Romeo Castellucci, one of the most original living opera directors.

Castellucci served it up pitch black: stonings, child murder, clouds of bone dust, culminating in ‘a chorus of last beings’, who are arranged into a terrifying high-renaissance tableau of writhing limbs and flesh – everyone featureless and on all fours – then sucked up into the beyond. Currentzis, meanwhile, had more chance to show off his talent for making stuff sound incredible in the Bartok, bringing the whole internal drama of Duke Bluebeard’s Castle to iridescent life within the pit with the extraordinary Gustav Mahler Jugendorchester, while Castellucci flashed fire upon an obsidian stage flooded with water and an eclipsed sun blazed across the backcloth.

Currentzis’s presence was controversial. The press were up in arms that he hadn’t distanced himself more from Putin (Russia funds his ensemble MusicAeterna). There were calls for his cancellation, for a termination of the production. Never mind that the composer of the opera he was conducting had dedicated a work to Hitler in 1944 and, in 1939, had taken up the Nazi’s call to rewrite Mendelssohn’s Midsummer Night’s Dream to remove the Jewish elements.

That makes it sound very much like Orff was a Nazi. He wasn’t. As you’ll learn from Tony Palmer’s gripping documentary O Fortuna (available on YouTube), he was merely an opportunist with unfortunate interests. It wasn’t a great time to be into Bavarian folk songs, primordialism, pedagogy and musical archaeology (check out his lush 1925 adaptation of Monteverdi’s Lamento d’Arianna). Orff’s crime then was to do far too well – suspiciously well – during the Third Reich, rising to be the third most important composer after Richard Strauss and Hans Pfitzner.

You can see why the philosophy of Origen that ends De Temporum, in which even Lucifer himself is finally reconciled and forgiven by God, was so attractive to someone as compromised as Orff. A hushed polyphonic viol music, which Orff had written when he was a student, swaddles this one rather moving final scene.

There was a time when Mahler was considered almost as vulgar as Orff. I see no reason why we ever aesthetically uncancelled the Second ‘Resurrection’ Symphony. I came away from an astonishingly vivid performance of the work by Simon Rattle at the Proms last week feeling quite dirty. But then I caught up with Castellucci’s mind-boggling realisation for Aix Festival online on Arte.TV in which the symphony, conducted by Esa-Pekka Salonen, soundtracks the cool, calm, exhaustively detailed exhumation of a colossal mass grave. The quiet, alarming realism cuts right through the bombast and sentimentality. Stripped of its need and ability to play-act, the music begins to emit a much subtler and more ghostly energy, transforming from garish melodrama into something approaching the quality of memory. Scandalously Castellucci has still never directed an opera in this country.