Food surplus management requires strategies that reduce environmental impacts while maintaining economic viability and efficient resource use. The purpose of this study is to assess whether freeze-drying can serve as a food-grade upcycling pathway that retains surplus food within the food system (waste prevention), compared with anaerobic digestion (AD) as a downcycling pathway to the waste sector for energy and nutrient recovery. A prospective attributional Life Cycle Assessment (LCA), combined with an discounted cash-flow (DCF) investment appraisal, was applied to three high-volume surplus products, eggplants, mushrooms, and grapes, currently diverted to biogas production in Denmark, using the functional unit “treatment of 1 ton of food surplus”. Under the current Danish energy mix, freeze-drying exhibits higher environmental impacts than AD, with global warming impacts ranging from 289 to 333 kg CO 2 -eq. per ton of surplus treated, compared to 125 kg CO 2 -eq. per ton for AD. This difference is primarily driven by the high electricity demand of freeze-drying. When modelled under a low-carbon electricity scenario dominated by wind power, the climate footprint of freeze-drying decreases to 31–36 kg CO 2 -eq. per ton (approximately 90% reduction), whereas AD remains comparatively stable at approximately 112 kg CO 2 -eq per ton... Dry matter content is identified as a key determinant of environmental efficiency, as products with lower dry matter require more energy input for moisture removal. From an economic perspective, freeze-drying requires substantial upfront capital investment, ranging from approximately €5–8 million depending on scale, but can generate positive long-term returns through the production of shelf-stable, food-grade ingredients. At a 6% discount rate and a baseline selling price equal to 2× production cost, Net Present Values (NPVs) range from strongly positive (approximately €8–19 million) under integrated surplus ownership and large-scale operation to negative values (approximately –€3 to –€6 million) in mid-scale configurations requiring external feedstock procurement. Sensitivity analysis shows that higher selling prices substantially improve financial viability across scales. Overall, the results show that while AD currently represents a lower-impact option for surplus food treatment under fossil-intensive electricity systems, the relative performance of freeze-drying improves markedly in low-carbon energy contexts. These findings indicate that the environmental competitiveness of electricity-intensive food-grade upcycling pathways is strongly coupled to energy system decarbonisation. Retaining surplus food within the food system through upcycling may therefore represent a context-dependent complementary strategy, warranting consideration alongside biological treatment pathways in future sustainable food system strategies. • Freeze-drying represents a food-grade upcycling pathway for surplus food. • Anaerobic digestion is environmentally preferable under current electricity systems. • Freeze-drying becomes competitive as electricity systems decarbonise. • Dry matter content strongly influences environmental efficiency in surplus upcycling. • Illustrative meal examples link surplus upcycling, energy transition, and food provision.
Thomsen et al. (Sun,) studied this question.