A method and apparatus for estimating a heating value of a biological material. The method includes irradiating of the biological material with X-ray radiation of at least two different energy levels, measuring of an amount of radiation transmitted through the biological material at these energy levels, and measuring fluorescent radiation emitted by the biological material when irradiated at these energy levels. A final estimate of the heating value is then determined based on a preliminary estimate of the heating value of the biological material based on the measured transmitted radiation and a correction value based on the fluorescent radiation.