Bach's Orgelbüchlein, Spitalfields Festival, review The Orgelbüchlein (Little Organ Book) of the great JS Bach lay unfinished when he died. The aim of the Spitalfields Festival's Orgelbüchlein Project is to finish it. That's no small task. Bach planned to compose 164 pieces, each based on a hymn tune or "chorale" of the Lutheran church, but completed only 46. By 2017 the Festival hopes to have 118 newly written pieces to fill those gaps. At this concert, in the St Peter ad Vincula chapel in the Tower of London, we heard five of the latest attempts. Complementing the meditative tone was a selection of sacred songs by Purcell and his contemporaries. Counter-tenor Tim Travers-Brown sang them with grace, without exaggerating the metaphysical conceits of the poetry. He was deftly accompanied by lutenist David Miller, an old hand who knows just where to amplify Purcell's harmonic spice with his own. That was the straightforward bit of the evening. The new pieces were more puzzling - inevitably, because completing Bach's cycle is a different sort of project to finishing, say, the Art of Fugue. Bach's cycle is an expression of belief as much as a musical statement, and his listeners would have known the raw material off by heart. Yet Bach was careful to make sure the old tunes were audible - as we were reminded at this concert, where we also heard five of those originals. These little masterpieces had a tremendous variety of mood, in line with the message of the text: joyous and ringing for In Dir ist Freude, penitential and tortuous for Christ lag in Todesbanden. In the hands of organist Christian Wilson they emerged with lovely rhythmic springiness and an enticing array of colours - as did Bach's tremendous E flat Prelude and Fugue, which bookended the concert. A contemporary composer is hard put to match that confidence, and the two contributions from Guy-Olivier Ferla and Vincent Paulet didn't try. They buried the melodies under existentialist meditations, which seemed absolutely contrary to the spirit of the enterprise. Roxanna Panufnik's somewhat bluesy setting was closer, but best of the bunch were Francis Pott's touchingly modest setting of Schmucke Dich and David Coonan's Jesus Christus unser Herr. Coonan's piece had a cleverly dramatic shape in the way it aimed for a glowing affirmation, failed and then succeeded, before returning to its questing, unquiet opening. It reimagined the musical symbolism of Bach's pieces, but in terms a sceptic could understand. The Spitalfields Festival runs until Dec 17. Tickets: 020 7377 1362; spitalfieldsmusic.org.uk