Complex sentence: He said that by the time of his death, Rilke had turned into "a delicate, well-matured liqueur suitable for grown-up ladies", but that his work is "too demanding" to be "considered relaxing".
Split into simpler sentences: He said that by the time of his death, Rilke had turned into "a delicate, well-matured liqueur suitable for grown-up ladies". However, his work is "too demanding" to be "considered relaxing".