You started your Beethoven series in the 1980s with Liszt’s transcriptions of Beethoven’s symphonies. Why did you start with these rather than the sonatas?
When I was a child I used to play four-hand transcriptions of Beethoven's symphonies with my mother. Later I played by ear and made my own transcriptions, then in Nadia Boulanger's keyboard class [at the Paris Conservatoire] we used to sight-read Liszt transcriptions. When I was asked to make the recording of the Beethoven symphonies I had to be careful as I already had my own transcriptions in my mind. But I was absurdly fascinated by these pieces.

How do they compare to the sonatas?
What Liszt did with the transcriptions are like the continuation of Beethoven after the Hammerklavier Sonata. They sound exactly like later Beethoven piano writing. I didn’t even think once that it was a transcription – even though Liszt had been extremely careful to be faithful to the score – I had the feeling that it was directly for the piano. The only problem is the Ninth Symphony, where you should have three or four hands!

So Liszt did a good job…
I think we’re a little bit unjust to Liszt today because if you listen to his pupils like Arthur De Greef they didn't play in a virtuoso way. They played in a very big musical kind of way, with big lines. It’s not a virtuoso playing – the music is the first thing. With Liszt we have been a bit dazzled by his virtuoso side but his later works are not at all virtuosic. He had this of course, but what he did later was to become more and modest with virtuosity.

And in the last few years you've recorded Beethoven's sonatas for the first time. Do you have a favourite?
The 32 sonatas are like 32 planets, so different. The richness and the fantasy of Beethoven is a real joy for a pianist to record. I absurdly adore the Hammerklavier and it’s an incredible world by itself. I would tend to say that all the sonatas are gravitating around this one. It’s like a sun.

What are the challenges of recording all his music?
The main thing is to be very near the score, what Beethoven has written. And after the Waldstein, or Appassionata even, I think the conception of Beethoven exceeds the possibilities of the piano. When I think of the big expanses that exist between the two hands, one in the bass and the other in the very high reaches of the piano and nothing in between: this is sometimes very difficult to do well because it shouldn’t sound ugly. You have to imagine there is something in the middle – something that exists only in your mind. The later sonatas are extraordinary – but I wonder if it is really possible to play them well. It’s always a question mark for me.

Interview by Rebecca Franks

Audio clip: Beethoven/Liszt: Symphony No. 3 - Allegro con brio

CD: Beethoven/Liszt: Symphonies Vol. 4: Symphony No. 3 in E flat
Idil Biret (piano)
Naxos 8.571263

Related links:
Conductor Semyon Bychkov on Wagner's Lohengrin
Violinist Janine Jansen on her 2009 RPS win
Violinist Nikolaj Znaider discusses Schoenberg, Brahms and Korngold