As was the case with his former teacher Joseph Haydn, Ignaz Pleyel's output of keyboard trios peaked in the 1790s. The earliest trio on this release, the Trio in E minor Ben 435, was one of six works that appeared in 1788, the set quickly being brought out by no fewer than six major publishing houses in that year and often reprinted thereafter. But then the trios Ben 441 (C major) and 442 (F minor) formed part of a group published in two sets of three in 1790 and 1791, and the other piece on this disc, the Trio in A major Ben 448 (1794), is one of no fewer than eighteen trios that Pleyel wrote for George Thomson in that decade. Thomson is well known for his role in commissioning folksong arrangements from the likes of Kozeluch, Haydn and Beethoven. While Pleyel participated in this project, which eventually yielded several hundred arrangements, his eighteen trios for Thomson also included movements based on Scottish airs.

Indeed, the representative of this group of works, the Trio in A major, might be a good place for a listener to start with this CD. It is the middle movement, a ‘Rondo Ecossois’ in A minor, that features the local colour, and one can easily imagine the relish with which players across Europe would have tackled it, since it is not hard for present-day listeners to grasp its picturesque attraction. The tune is syntactically ‘lame’, unexpectedly sitting down at cadence points, and its unison presentation by the three players emphasizes the material's lack of tractability. Nor can there be any coda at the end – the tune simply stops, unable to extend itself. The episodes in between offer us the syntactical flexibility of the modern style, for instance through short-range dialogue between violin and piano, though the composer then takes great care to dissolve such eloquence in readiness for the return of the unpolished Scottish air. The brief finale is based around one of Pleyel's catchiest tunes, of nursery-rhyme simplicity. That it represents a manufactured ‘naturalness’, however, unlike the tune of the second movement, is made clear by the way its material can be manipulated in the long retransitions that are typical of rondo form. But a greater contrast is found in what precedes the exotic air, a gorgeously scored Allegro moderato. It features the sort of untidy profusion of riches that we find in Haydn's opening trio movements from this time. Inspirational playing by Trio 1790 brings out all its colours, from sinuous counterpoint to horn calls, even if at times they push the music rather hard.

The earliest work on the disc, the E minor trio, has none of this casual richness. Its first movement is utterly dominated by a motto sternly intoned by the piano at the start and soon becoming the subject of earnest discussion amongst all players. Agitated figuration and sigh figures add to the sense of weight, and only a hovering second subject seems to offer respite. A common critical gambit on the instrumental music of this time suggests that composers are more able to be themselves when writing in minor keys, that they achieve an authenticity of personal expression when not compromised by the need to wear a fixed major-key smile. This may not be entirely anachronistic, given the remarks of, say, a C. P. E. Bach, who clearly preferred pleasing himself in private to writing for mass consumption, and felt he lost something of himself in having to do the latter. Yet it is easy to overlook the fact that the range and type of expression found in minor keys is often narrower than what major-key movements can offer. Compared to the plenitude of the first movement of our Trio in A major, there is an obsessiveness about the musical behaviour here, for all the impressively sustained intensity. Comparable movements would include the opening Allegros of Mozart's Piano Quartet in G minor, k478, which also sets off with a stern motto figure, and Haydn's own Trio in E minor, hXV:12, published one year after Pleyel's work in 1789. In other words, such an idiom can be just as expressively ritualistic as a cheery rondo finale.

Another aspect of minor-key usage at this time that is not always understood involves its tendency to reach back into the past for technical means. The chains of suspensions and falling sequences in the current movement are typical, and the finale, which retains the minor mode, offers further examples. It too is built from a chiselled motto, which in fact seems to be extracted from the first movement's main figure. But this is lighter on its feet, and interacts with a bass line made up of sighing figures. Then as early as the first consequent phrase Pleyel treats the two lines in invertible counterpoint. Towards the end, the motto is played in stretto and then in a long chain of falling parallel chords which create a positively gothic sound. Altogether this minor-mode manner is more process-driven than the major-mode equivalent, less likely to consider matters from an alternative point of view, as it were. Trio 1790 on their lean-sounding period instruments are well equipped to emphasize such a driven quality, which includes some surprisingly full and aggressive writing for keyboard. Yet they also offer an affecting version of the central Andantino in the submediant major, even if occasionally the string players' swelling on longer notes may strike the less sympathetic listener as mannered. The proportions of this simple lyric movement seem perfectly judged as a respite from the surrounding storm and stress.

Less obviously well judged is the fact that Pleyel sets the slow movement of the C major trio in the same key as the outer movements. Andreas Friesenhagen puzzles over this in his recording notes, which are of cpo's usual excellent standard, both informative and thought-provoking. This is also a much slower and longer movement than the Andantino of the E minor work, and, being set in variation form, features many affirmations of its tonic. The theme itself foregrounds harmony rather than expansive melody, being written in a noble chorale style. The first variation then takes this attribute in an unexpected direction: violin, cello and piano right hand break the long durations into pianissimo staccato triplets in an ethereal register, while piano left hand plays a steady bass line that provides the textural glue. The effect is enchanting, but it seems an odd decision to place this treatment so early. Variations 2 to 4 rotate melodic leadership (Variation 3 a minore in which the cello's prominence is rather muffled by the recording engineers), while Variations 5 and 6 are more figurative in style. Normally a treatment like that found in Variation 1, which ‘abstracts’ from the theme, would not arrive until later in the cycle. Also a little puzzling is the brevity of the Presto rondo that follows as finale.

On the other hand, the first movement of this work is as expansive as one would expect a C major opening movement to be. It even starts with a brief fortissimo introduction at Adagio tempo – though this is needed because the initial Allegro molto material is poised on the dominant, a trait that is shared by many subsequent passages. Its variety of material and gesture is, once more, just what we don't find in the first movement of the Trio in E minor. The development section is notable for the way in which it is taken over by a figure that had previously appeared an incidental part of the discourse; the single ‘theme’ that theorists like Koch assured their readers a movement would be built on is nowhere to be heard. From a social point of view, though, such unpredictability of thematic occurrence in a central section may be precisely the point: no one can know in advance which ideas or ‘voices’ will prevail in the heat of debate. The figure that dominates the section is short and cycles around in a repetitive loop. Such frenetic repetition of a brief motive is one of Pleyel's fingerprints, in fact. It is similar to the technique of which Boccherini was so fond, but whereas his loops often have a hypnotic, sensual effect, Pleyel's tend to energize the music.

Yet in the final work on the disc, the Trio in F minor, Ben 442, a broad violin cantilena that acts as second subject includes a loop that is much more hesitant. It takes its place in a heavy, brooding movement that is less tight thematically than the equivalent Allegro of the E minor trio but still often returns to its opening material, which is treated like a ritornello. Trio 1790 certainly cannot be accused of underplaying their hand – and it is quite understandable to want to be forceful advocates for such splendid and little-known music – yet I find their playing at louder dynamic levels rather undifferentiated. All forte passages tend to be attacked with the same force. This cannot be because they are clinging to an absolute respect for the score as the determining agent in every performing decision they make; they show impressive flexibility in articulation, sometimes taking their own route against the indications of the sources.

A remarkable feature of this movement is that it turns to major at the point of recapitulation, very unusually for the opening movement of a minor-key work. Again, we must avoid interpreting this according to the usual maudlin imperative of self-expression, as if moving to the major was simply pandering to the forces of the market. As Wye J. Allanbrook never tired of pointing out, favouring the major mode in the later eighteenth century was a ‘striking new trope’ (see ‘Mozart's Tunes and the Comedy of Closure’, in On Mozart, ed. James M. Morris (Cambridge: Cambridge University Press, in association with the Woodrow Wilson Center Press, 1994), 175). In fact, Pleyel's shifting to major is striking precisely because it comes ‘too soon’, forcing modal reinterpretation of the entire sequence of opening ideas. It is not surprising when this material later returns in the recapitulation first of all in D flat major and then indeed in F minor, as if absorbing the shock waves before the major mode can achieve its full resolving effect. Then in the coda the violin plays a broad tune that soothes the troubled breast, cadencing repeatedly in F major in a radical simplification of utterance.

The Tempo di Minuetto finale reverts to F minor, using chromatic falling tetrachords, an obsessive dotted-rhythmic anacrusis and further large-scale invertible counterpoint to underline once more the mode's affiliations with older techniques. The major-mode trio section offers a simpler, more ‘natural’ style centred on melodic eloquence, and after an ornamented return of the first section, the composer repeats his first-movement device. The opening is translated into major, and a touching simplification of means is soon felt: the final bars are written in pure pastoral texture, with two melodic lines playing in parallel intervals and an oscillating-octave pedal in the bass. This movement sums up well the attractions of this release: these are expressively satisfying and technically demanding trios, compellingly played by Trio 1790, even if they sometimes seem a little brisk, a little short on dolcezza.