Playing the opera at the piano is a practice that requires specific skills: in particular it is a matter of rendering the idea of the original version for orchestra, limiting itself to the piano only. Obviously, it is not a question of "imitating" the sound of the orchestra, but rather to "evoking" it through choices of piano instrumentation and instrumental timbre appropriate to the effect we intend to simulate.
Mascagni's "Cavalleria Rusticana" (1890) and specifically the orchestral introduction to the choir "Gli aranci olezzano".
The piano reduction that is usually used is the classical one, made by Leopoldo Mugnone for the original Sonzogno edition of 1891. We note that already in the first exposition of the main theme the melody doubled in octave, while the left hand performs an accompaniment which requires continuous jumps between the bass and the internal parts.
Subsequently, in correspondence with the first entry of the choir, the writing is even more massive, especially in the left hand.
It is not possible to make excessive simplifications to "facilitate" the piano part, because this would preclude the effect of evoking the orchestral sound: it is not possible, for example, to play the melody with single keys, avoiding the doubling of octave and the filling in agreements in some moments of support. In fact, if we look the orchestral score, we note that initially the theme is given to all the strings, with doubling of octave between violins (first and second in unison, plus the oboe 1) and violas and cellos. The effect is already vigorous and well sustained in sound, as can it easily seen when listening.
In the following ripresa, at the entry of the choir, the orchestral writing becomes even more massive, with the entry of all the winds (including the blaring trumpets), arranged even on three octaves, while the accompaniment is marked by percussion and tuba (in addition to the basses of the strings and winds) and in particular with the heavy chords of the trombones.
All this cannot be achieved with a light and chamber sound, but with a powerful and massive sound, although always soft and never strained. The suggestion of orchestral sound must accompany the sonorous idea of the pianist, ready to accompany even a large choir, in this festive and luminous page that does not yet predict the imminent tragedy what will be told in the opera.
We can hear a beautiful orchestral performance, conducted by the author himself in 1940 at the Teatro alla Scala in Milan, at this link.