Reduction of production losses and increasing resource efficiency is needed to improve sustainability of the food supply chain. One approach to reach more resource-efficient, circular food systems is blending and processing side streams, especially when blending increases their value through compositional, nutritional or functional synergies. In this perspective we present a case study for valorizing sunflower oil press cake and whey. As the need for specialty products grows, small and medium-sized seed oil producers will be challenged with by-products. Similarly, small and geographically scattered dairy companies are faced with inadequate supply chains not allowing handling and downstream processing of whey. By combining two side streams, and applying simple processing steps and novel fermentation approaches, it would be possible not only to improve circularity of the value chain, but also to develop innovative ingredient platforms. A series of solutions appealing to various end users, from beverage producers to bakeries and snack applications, can be developed from fermented side stream blends when specific demands to ensure food safety and appropriate sensory quality are met.