This paper presents a linear mixed integer modeling approach for basic components in a biomass supply chain including supply, processing, storage and demand of different types of biomass.The main focus in the biomass models lies on the representation of the relationship between moisture and energy content in a discretized framework and on handling of long term processes like storage with passive drying effects in the optimization. The biomass models are formulated consistently with current models for gas, electricity and heat infrastructures in the optimization model 'eTransport', which is designed for planning of energy systems with multiple energy carriers. To keep track of the varying moisture content in the models and its impact on other biomass properties, the current node structure in eTransport has been expanded with a special set of biomass nodes. The Node, Supply, Dryer and Storage models are presented in detail as examples of the approach. A sample case study is included to illustrate the functionality implemented in the models.