This paper reports the implementation of the "mean age of air" (MAA) concept into the computational fluid dynamics (CFD) code Fluent through user-defined functions to assess ventilation efficiency inside forced-ventilation food plants. Two transient methods and a steady-state method based on the resolution of an additional scalar transport equation were implemented and compared with experimental and numerical data obtained by Bartak et al. [Bartak, M., Cermak, M., Clarke, J.A.. Denev, J., Drkal, F., Lain, M., Macdonald, I.A., Majer, M., Stankov, P., 2001. Experimental and numerical study of local mean age of air. In: Proceedings of the 7th International Building Performance Simulation Association (IBPSA) Conference, Rio de janeiro, Brazil; Bartak, M., Beausoleil-Morrison, I., Clarke,J.A.. Denev, J. Drkal, F., Lain, M., Macdonald, I.A., Melikov, A., Popiolek, Z., Stankov, P., 2002. Integrating CFD and building simulation. Building and Environment, 37. 865-871] for a 45 m(3) test room. As the steady-state method led to the best compromise between accuracy of results and computation time. this method was then used to characterize ventilation efficiency inside a pilot cheese ripening room and two modern sausage dryers of large height. In light of the results presented, local MAA is a better and a more sensitive parameter than mean air velocity for highlighting areas with inadequate ventilation, and thus for assessing ventilation efficiency in industrial food plants. (c) 2008 Elsevier Ltd. All rights reserved.