JC Bach's symphonies aren't just important because of their influence on the young Mozart. They're signature works of the 18th century – and his G minor symphony, Op 6 no 6, is arguably the darkest and most dramatic he composed

We think of the symphony in the 20th and 21st centuries as the apogee of radicalism and experimentation in the form, as composers strove to create new kinds of thinking and feeling after it was thought to have exhausted itself (not true! – as you’ll know if you’ve been following this series so far). But to experience a true sense of adventure, novelty and symphonic discovery, you have to cast yourself back to the mid-18th century, and an era in which this self-sustaining species of public instrumental music was still forming itself in the minds of composers and the ears of listeners.

And that’s where this week’s symphony, Johann Christian Bach’s G minor work, Op 6 No 6, comes in. Composed in the 1760s (definitely before 1769), it was almost certainly on the programmes of the concerts that Bach and fellow composer and impresario Carl Friedrich Abel put on in their series of prophetic and fashionable concerts at Carlisle House in London’s Soho, then St James, and finally at the bespoke concert room they had built at Hanover Square. JC Bach – the “London” Bach: Johann Christian had moved to Britain in 1762, initially to write operas for the King’s theatre, and was music master to Queen Charlotte, but subsequently focused on concertos and symphonies – arguably did more to cultivate an appetite and an audience for instrumental music than anyone else of his time. Consisting mostly of Bach’s own music, the performances became essential events in Georgian London’s social and cultural calendar, even inspiring this paean from a contemporary:

Where Carlisle house attracts the light and gay And countless tapers emulate the day, There youth and beauty chase the hours along, And aid time’s flight by revelry and song; …… Then worn with pleasure, forth the revellers stray, And hail with languid looks the new-born day: – They seek their homes; – there, weary with ennui, Joyless and dull, is all they hear and see; Spiritless and void, of every charm bereft, Unlike that scene of magic they have left, They childe the lingering hours that move so slow, Till the night comes, when they again can go And mingle in the enchantments of Soho.

Plus ça change … but in the 18th century, alchemical delight was reached through symphonies rather than through anything more – well, chemical. And one of the pieces that would certainly have conjured a “scene of magic”, albeit a turbulent sorcery rather than anything more comforting, was the G minor symphony, Op 6 No 6. In three minor-key movements – including, in its central Andante, piu tosto adagio, one of the longest symphonic movements JC Bach ever wrote – this work reveals Bach’s major symphonic innovations as well as creating an explosive burst of the sturm und drang (“storm and stress”) passions that were the dark side of the 18th century’s sense and sensibility.

Bach’s music was designed to appeal to its audiences. His tunes, his simple harmonies and his innovative use of orchestral colour were all supposed to enliven, entertain and elevate his listeners when they first heard his new pieces. But that deliberate attempt to make instrumental music an embodiment of instantaneous feeling and passion instead of the intellectual rigour and contrapuntal complexity of an earlier era – above all, that of Bach’s father, Johann Sebastian, and in London the imposing legacy of Handel – was much more sophisticated than posterity would give him credit for. After his death, Bach’s music was scarcely heard in the 19th century, yet in his day JC was among the most famous composers in Europe. But somebody who did realise how Johann Christian was opening up new possibilities for the expressive potential of instrumental music was Mozart, who heard Bach’s music when he came to London in 1764 at the age of 8. Mozart arranged Bach’s music, he played at the keyboard with him – and the young man's own music was transformed by the encounter. Mozart later memorialised JC Bach in the slow movement of his A major piano concerto, K414, produced just after he had heard the news of Bach's death in 1782, basing the piece on one of the elder composer's overtures. “What a loss to the musical world!” he wrote. It was JC Bach, much more than Haydn, who was the most important influence on the young Mozart’s style and ideas about the form.

In JC Bach’s G minor symphony, there are moments when you feel you’re hearing premonitions of Mozart – most clearly in the atmosphere of headlong intensity in the first movement, which Mozart seems to recreate and remember in his own G minor symphony, K183, from 1773; there’s a specific musical connection between the way one of Bach’s melodic ideas emerges (a rocking semitone in the strings) and what he does with it in the central and most stormy section of the movement, and what Mozart does with a similar idea in his visionary C major symphony, K338. There’s even a connection between the slow movement’s opening C minor tune and Wolfgang’s C minor piano concerto, K491, whose first three notes are exactly the same.

But better to forget what you know – or what you think you know – and instead try to experience JC Bach’s symphony as those listeners in Soho must have done. Brace yourselves for the compressed edge-of-the-seat drama of its first movement, the unsettlingly emotional slow movement (with a final appoggiatura, a harmonic sigh that wounds its final cadence, mimicking the very end of the St Matthew Passion by JC’s father), and the minor-key rocket of the finale, propelled by horn-calls and explosions in the upper strings. The whole piece ends with a disturbing musical question-mark, a dramatic and sudden descrescendo from forte to piano. Bach doesn’t resolve the tensions in this G minor symphony, as later composers might have felt they had to; instead, he leaves the tempest he has just unleashed fizzing electrically in the air and in your imagination.

Best of all, you can hear this symphony in two differently but equally exciting performances by the Akademie für Alte Musik Berlin and Concerto Köln – interpretations that thrust JC Bach’s music thrillingly into the present tense.