What mattered to Koester was to "paint the sunlight [..]. Animal and environment […] appear as a unity, as a pictorial impression immersed in light and color. [Koester‘s charming animal scenes] show that the animals‘ individual physical aspect does not miss out in such a bath of reflections […]. It is all rendered with a broad and juicy brushstroke that shows the pure joy in sun and color. What a pleasure it is to see the flock of squatting ducks with their snow-white plumage and their lemon- and reddish yellow beaks in the play of light and shade. Every brushstroke proves the artist ‘s spirit and sense for color." (Dr. Paul Kühn, review of the exhibition at Kunstverein Leipzig , 1904, quote after Stein 1988, pp. 51f.).