"Referring to the compositional draft for "Sour Milk Sea", musicologist Walter Everett states that together the various chords suggest "a pentatonic minor scale on A, allowing B as a tritone-related ornament to E7".The song makes limited use of the expected A major chord, however, instead centring on E over the verses and D in the choruses, with the latter representing what Everett terms "the Mixolydian VII area".