Closing the Loop in Vitiviniculture and Spirit Production: From Grape Processing Waste to the Multifunctional Biochar

Viticulture, winemaking, and distillation industries produce substantial quantities of organic by-products (grape prunings, stems, marc-pomace, spent yeast, wine lees, distillation heads and tails, stillage), presenting both environmental challenges and promising opportunities for sustainable valorization. This narrative review offers a comprehensive analysis of the viticulture, winemaking, and distillation processes, along with the characterization of their solid and liquid by-products. Furthermore, it examines the chemical composition and mentions main valorization strategies for these residues, emphasizing their potential both as feedstocks for biochar production and as sources of valuable solvents. Additionally, various applications of biochars are explored, with particular focus on biochar derived from grape pruning and grape pomace-marc biomass, highlighting its effectiveness as a sorbent for environmental contaminants. Moreover, a broad range of biochar activation and modification methods that enhance physicochemical properties and expand functional applications is reviewed. Solvent-based biochar modification is also examined in order to introduce a novel concept: employing grape distillation liquid by-products (heads and tails fractions) to activate biochars made from grape prunings and pomace, creating a high-value sorbent while simultaneously valorizing two major waste streams. This dual-use strategy offers a new pathway for circular resource management within the viticulture and winemaking sectors.