‘Too highly seasoned’, ran an early review of Mozart’s six ‘Haydn’ Quartets. ‘And whose palate can endure this for long?’ No works contributed more to his reputation as a ‘difficult’ composer than these (by the standards of the day) densely composed masterpieces. In his dedication Mozart famously wrote that they were ‘the fruits of long and laborious endeavour’. And it’s my hunch that the A major, K464 – Beethoven’s favourite – cost him more effort than any. For all its surface nonchalance this is Mozart’s most cerebral and concentrated quartet, contrapuntally intricate (not least in the Minuet), often highly chromatic. With their lean, period-influenced sonorities, vital, fluid phrasing and care for the subtleties of Mozart’s complex part-writing, the Casals give one of the most satisfying performances I’ve heard of this often elusive work.

Other groups, including The Lindsays (ASV, 11/98) and, on period instruments, the Mosaïques (Naïve), bring a warmer, more relaxed style to the triple-time first movement of K464. Both here and in the Minuet the Casals are brisker, edgier. But their absolute textural clarity (never a hint of bland homogenisation) and careful weighting and colouring of each line, allied to an unusually wide dynamic range, bring rich rewards. From Mozart’s deceptively formal opening they think long, gliding and soaring over the bar line, always urging forwards. The Casals Quartet’s Mozart is never merely comfortable. The Minuet’s fierce harmonic clashes sting and scald as you’ll rarely hear, while the cello’s forceful ‘drum’ ostinato in the Andante creates an uncommonly disturbing disjunction with the serenely singing lines of the upper instruments.

The Casals bring the same questioning intelligence and imagination to the other quartets. The outer movements of the Hunt (K458) bristle with sinewy impetuosity, each phrase quivering with life, while the Adagio, unfolding in typically long eloquent spans, has a rarefied inwardness. In the first movement of the D minor, K421, moments in this performance that linger in the memory include the ominous pp mystery of the development and the fragility of the second theme when it returns, darkened in the minor, in the recapitulation. As ever, Mozart’s dynamics are scrupulously differentiated. Choosing a flowing tempo (many quartets get bogged down here), the Casals float the lines of the Andante naturally across the many rests. The Minuet is fierce, uncompromising, the serenading Trio, often a cue for winsomeness, touching in its sweet simplicity. And while the Casals bring an inventive variety of colour and character to the theme-and-variations finale, they characteristically emphasise continuity, with minimal gaps and contrasts of tempo between the individual variations.

Throughout the disc repeats are always rethought, sometimes enhanced by graceful touches of embellishment from leader Abel Tomàs Realp. The Casals rightly take both repeats in the tragic first movement of K421 though – perhaps for reasons of space – omit Mozart’s prescribed second repeats in the outer movements of the Hunt. The recorded sound is vibrant and immediate. It’s absurd, of course, to speak of a winner in such a competitive field. Enough to say that if you like your Mozart taut and urgent, with no concessions to Mozartian ‘charm’, you should find these brilliantly executed performances as riveting as I do.