Decarbonisation of tunnel ovens for baking purposes: Review and future prospects

Abstract

Industrial tunnel ovens are among the most energy-intensive equipment in large-scale bakeries and a significant contributor to greenhouse gas emissions. This review synthesises experimental, computational, and industrial evidence on tunnel-oven performance and decarbonisation options, focusing on gas-fired, electric, and emerging heating technologies relevant to continuous baking. Studies were assessed with respect to thermal performance and product-quality outcomes. To enable consistent comparison across studies, thermal performance is interpreted using defined system boundaries. Supplied heat is taken as burner fuel input on a lower heating value basis for gas and hydrogen systems, or electrical power delivered to heating elements for electric systems. Useful heat absorbed by the product includes sensible heating of the dough and latent heat associated with moisture evaporation. Under these boundaries, reported product heat utilisation varies widely and can fall to around 16% in high-temperature direct-fired tunnel operation, indicating substantial losses through exhaust gases and heat transfer to the oven structure and surroundings. Electrification through resistance heating improves controllability and avoids combustion losses, although reduced radiative heat transfer can affect crust development. Hybrid concepts combining resistance heating with infrared or convection show potential to maintain surface quality while reducing energy use. Advanced electrothermal approaches, including induction, microwave, and ohmic heating, remain constrained by scale-up and control challenges and lack full-scale validation. Hydrogen combustion represents a possible longer-term pathway, but direct evidence for hydrogen-fired tunnel ovens in baking remains absent. Overall feasibility depends on grid carbon intensity, energy prices, and retrofit constraints.