It is, of course, perverse to write a novel about one of the greatest musicians who has ever lived. Johann Sebastian Bach is the voice of God in music, the father-figure for all the composers that followed. This Easter there are performances of his St Matthew Passion in Birmingham, Cardiff, Edinburgh, London and Sheffield; in Amsterdam, Berlin, Budapest, Montreal, Vienna and in Leipzig, where he worked as the choir-master, or Cantor, from 1727-1750. 

Bach is one of the top three most requested artists on Desert Island Discs (along with Mozart and Beethoven), with guests often asking for The Brandenburg Concertos, the Cello suites or The Goldberg Variations. His image is on ties, tote-bags and T-shirts; beer mugs, baseball caps and bumper stickers (“BACH OFF!”). You can buy his figurine in three different types of chocolate and a badge with him in dark glasses impersonating the Terminator (“I’LL BE BACH”). 

But what was he like as a living, breathing human being?

The statue outside St Thomas’s Church shows an old, pious, austere and respectable pillar of the community. But who was this man before he became the great “Bach”?  Could one get behind the religious reputation to imagine a working musician, as earthy as he was sublime, with a rambunctious family around him? This was the starting point for my new novel, The Great Passion, a project which has obsessed me for the last five years. 

It’s clear that, as well as being a devout Lutheran, Bach was a man of appetite. The two things are not mutually exclusive.  A surviving bar bill from 1713 shows that he drank 32 quarts of beer in two weeks. That’s four and a half pints a day. Then there was sex. He had 20 children. Over the 13-year period from 1722 to 1735 his second wife, Anna Magdalena, gave birth 11 times. There was hardly a time when she was not pregnant. One wonders whether Bach ever left his wife alone.

Johan Forkel, his first biographer, talks of how the extended family would meet for a musical evening, start off with a chorale and then the mood would change with improvisation, drolleries and popular songs, some of them positively risqué. There’s an early wedding Quodlibet, for example, that’s full of double entendre:

Große Hochzeit, große Freude…
(Great big wedding, great joy)
Große Degen, große Scheide
(Large dagger, large scabbard)

Scheide is the standard German term for vagina. The whole song consists of improbably big items – enormous arrows, accommodating quivers, full-size donkeys with huge “tails” and large maidens holding open “wreaths”. You get the idea.

And it’s not just a male thing. Anna Magdalena Bach enters another wedding doggerel into her musical album of 1725. This argues that however well you protect a henhouse from intrusion it still needs to have its holes bored – a stanza considered so dubious that no English translation of it was published until 1990.

Bach’s passion extended to his temper. When he was 20, he got into a sword fight with a fellow musician, calling his colleague “a prick of a bassoonist”. There are accounts of him taking off his wig in the middle of rehearsals and throwing it on the floor in a rage; and he couldn’t understand why some pupils were so slow to improve, telling one keyboard player: “IT’S NOT DIFFICULT. Just hit the right notes at the right time and the instrument will play itself.”