encapsulating process biomass production Biomass production, often represented 'R_BIOMASS_', is usually the optimization target reaction of constraint-based models, and can consume multiple reactants to produce multiple products. It is also assumed that parts of the reactants are also consumed in unrepresented processes and hence products do not have to reflect all the atom composition of the reactants. Formulation of a biomass production process entails definition of the macromolecular content (eg. cellular protein fraction), metabolic constitution of each fraction (eg. amino acids), and subsequently the atomic composition (eg. nitrogen atoms). More complex biomass functions can additionally incorporate details of essential vitamins and cofactors required for growth.