In the week when Culture Secretary Maria Miller told arts organisations across the UK to show her the money, it seems inappropriate to begin this review by commenting on the length of concert intervals – they are, after all, vital for venues to make a few pounds selling drinks to a culture-thirsty clientele. Nonetheless, the period separating the two halves of Angela Hewitt’s Art of Fugue performance was considerably longer than St George’s Bristol’s customary 25-minute break. Six months had passed since Hewitt began her journey through Bach’s fugal masterpiece, which I was fortunate enough to witness last October. The memory of that occasion was enough for me to secure my seat in the concert hall: and, of course, my half-time orange juice, too.

After such a long delay, the audience members was doubtless quite happy for their expectations to be prolonged just a little more by Hewitt’s first-half programme of Bach and Beethoven. My own enthusiasms were dampened somewhat, however, by a rather uninspiring (though technically impressive) Chromatic Fantasia and Fugue, BWV903. Throughout the colourful whirlpools of pianistic sound, I could not stop myself from imagining the sound of an organ piping away in a cathedral-style acoustic. In complete opposition to Hewitt’s Art of Fugue, this Fantasia really argued against piano performance of Bach’s organ works: the clustering of notes merged all too easily into an indulgent mush, although the piano’s enhanced dynamic capacities were imaginatively exploited by Hewitt’s feather-light touch. The added forward momentum provided by the fugue proved far more engaging, and Hewitt’s brilliant control of voicing – to be a theme all night – was both wonderfully impressive and expressive.

Beethoven’s Sonata in A flat Op.110 provided the proverbial meat in the concert’s Bach sandwich, although the musical main course was certainly still to come. The Moderato first movement is a beautifully simple entrée, a singing movement with nursery-rhyme-like passages. The music features occasional cadences high in the piano’s register, and the attention that Hewitt gave to them – almost awkwardly over-investing in them physically – seemed to me a touch affected. (In hindsight, and after being reminded just how musically dedicated Hewitt is in her playing, I can safely say that I was misguided – she is utterly genuine in her total immersion in the music.) The Allegro molto is assertive from the off: belligerent “parent” passages quickly quash the more quietly inquisitive, “child”-like musical arguments. A brilliant melodic line sweeping over an unsettled offbeat accompaniment was virtuosically handled, as this feisty movement burnt itself out quickly and bullishly. What followed was Beethoven at his most intrinsically, passionately, intensely tragic. The painful lamentation of the Adagio molto cuts right to the core of matters, exposing the inner turmoil of a desperate musical subject. The music slips exhausted into the final cadence, before rousing itself to begin a seemingly playful Fugue, whose subject returns some of the confidence of the second movement. This soon escalates in anger, though, as the fortissimo bassline breaks the shackles of the subject, crashes up the scale and eventually knocks everything into shape for the final cadence, though not before some ingenious subject-inversion from the composer.

Ingenious subject inversion is only the beginning in Bach’s Art of Fugue. In eighteen movements of complete technical mastery, Bach explores seeming unending creative expanses in his compositional mind, weaving a tapestry of fugal sound unlike any other. As she had in October’s concert, Hewitt preceded her performance (beginning with Contrapuntus XI) with a lengthy spoken exploration of the movements to be heard. This was again a fascinating and vital introduction, which provided the listeners with enough musical markers so as not to find themselves lost in a dense fugal forest. As she so rightly and insightfully stated, Bach’s music demands huge levels of concentration on the part of both performer and listener; indeed, as Hewitt guided us so expertly, so astoundingly, through the music, the concentration from the audience was practically tangible. As the music moved magically through mirror fugues, augmented canons, octave canons, canons in tenths, canons in twelfths, so the listener was transfixed in an auditory gaze that was as wholesome as it was intense.

Then came the anticlimax: the petering out of the final fugue that leaves off where the composer could not go. It is a bizarre and powerful moment. The long silence that followed the last haunting unfinished phrase had something gravely spiritual about it, and Hewitt’s request that applause be held until after her rendition of the chorale prelude &;ldquo;Vor deinen Thron tret ich hiermit”, BWV668 – allegedly dictated on the composer’s deathbed – was never likely to be transgressed.

It was a startlingly moving musical moment: one whose power was not diminished, despite the lengthy interval.