Once one is able to valorise residue streams, there will be a challenge to look for even better raw materials that contain a higher proportion of the previously called residue stream. Finally, one can try to optimise the culture on the field or even the genetic optimisation of the crop that contains more of that previously called residue component, and at the same time improve the crops processability by genetic means.

Good examples of genetic modification of primary crops have been obtained for the amino acid lysine in crops like potato (Voorst, 1999) and corn (Houmard, 2007). These improvements were initiated because of the application as animal feed ingredient. Recently, itaconic acid has been expressed in potato with the aim to use this as building block for the synthesis of methacrylate.

Primary residue streams such as wheat straw and other agricultural residues can be used for their cellulose content, but sometimes they still consist of other valuable components such as proteins as is the case for sugar beet or sugar cane leaves (trash), for the leaves of cassave, and other crops. Until now these plant components almost never had an economic application, but now have potentially become an interesting alternative for the fossil based resources.

DDGS and rapeseed meal are good examples of so-called secondary residue streams, i. e. residues that result from industrial processes (often in the food industry), and recently result from the biofuels industry. These fractions have similar compositions as primary residues with the logistic advantage that these streams are available from one point source. These streams therefore often have already some applications as e. g. compound feed components. It is not only that separation of components gives a higher value to each single component but also the removal of a component such as phosphate or potassium, that in too high concentrations have a negative value in actual compound feed applications, can help to increase the economic feasibility of biorefining primary and secondary residue streams.