Sustainability metrics, based on material efficiency, energy input, land use and costs, of three processes for the manufacture of methionine are compared. The petrochemical process affords DL-methionine while the two biomass-based routes afford the L-enantiomer. From the point of view of the major application, in animal feed, either can be used. The first bio-based route, developed by CJ Cheil-Jedang, involves the production of an L-methionine precursor, O-succinyl homoserine by fermentation followed by enzymatic reaction of the latter with methyl mercaptan. The second bio-based route involves the isolation of L-methionine from grass protein. Based on this concise evaluation of the sustainability metrics we conclude that both bio-based processe are potentially attractive sustainable routes for the manufacture of methionine. (C) 2014 Elsevier B.V. All rights reserved.