Micro-spectral analysis and fluorescence decay experiments of beech and oak chips as well as their main constituents lignin and cellulose are reported. While the lignin spectrum shows two fluorescence bands of almost identical intensity around 500 nm and 560 nm, the cellulose spectrum is dominated by a band around 500 with a less pronounced shoulder at 560 nm, whose intensity increases with the amount of residual lignin. Fluorescence decay kinetics are bi-exponential with lifetimes around 0.5 ns and 2.5 ns and an increasing contribution of the short-lived component with an increasing amount of lignin. Both data sets indicate that a quantification of residual lignin in cellulose samples obtained after decomposition of beech wood appears possible in a concentration range of 2-10 %. This may provide a non-destructive and label-free test of the quality of decomposition.