Small size (<1 MW) thermochemical plants producing electricity and heat are a convenient option for biomass-to-energy scenarios. It is required to improve these systems in terms of efficiency and flexibility, extending the feedstock specification and plant reliability. In this work the experimental results of the recent campaigns in the CRIBE gasification plant with out-of-specification feedstocks (pellets, vine prunings, rice husks, corn cobs, miscanthus) are described and discussed. The biomass properties are investigated and related to the technological operations and plant performance for defining the suitable ranges of their characteristics. The morphological parameters (size/shape), density, thermal and mechanical consistency of the material are crucial for the safe operation in the downdraft gasifier. The pretreaments (drying, size reduction, pelletization, mixing of different feedstocks) are necessary for operability and should be optimized considering the overall plant efficiency and costs. This will be evaluated with a process study.