This review examines the role of wood ash as an amendment in enhancing humus formation during the aerobic composting of food waste. Humus, a stable organic material derived from decomposed plant and microbial matter, is critical for soil health, carbon sequestration, and sustainable agriculture. However, optimizing humus production during composting remains a challenge due to variable feedstock quality and inefficient decomposition processes. Wood ash, a byproduct of biomass combustion, offers a promising solution by improving microbial activity, regulating pH, and supplying essential nutrients such as calcium, potassium, and phosphorus. The review synthesizes current research on the mechanisms by which wood ash influences composting efficiency, including its effects on microbial communities, carbon-to-nitrogen (C:N) ratio balance, lignin decomposition, and humic substance stability. Key findings indicate that moderate wood ash application (4–8% by weight) accelerates organic matter breakdown, enhances compost maturity, and increases nutrient retention without significant heavy metal accumulation. However, excessive use can lead to alkaline conditions, microbial imbalance, and potential environmental risks. A case study highlights the practical benefits of wood ash in composting, demonstrating improved temperature dynamics, pH stability, and nutrient enrichment at optimal dosages. Challenges such as heavy metal contamination, over-application risks, and long-term soil impacts are discussed, alongside recommendations for sustainable use. Future research directions include microbial community dynamics, feedstock-specific interactions, and standardized guidelines for ash application. This review underscores the potential of wood ash as a sustainable composting additive, offering insights for waste management, soil fertility enhancement, and climate change mitigation through improved humus formation.