Polyphenolic epicatechin esters are potentially attractive targets for lignin bioengineering because their copolymerization with monolignols could reduce lignin hydrophobicity and cross-linking to polysaccharides, or facilitate delignification by biomass pretreatments. To test this hypothesis, we biomimetically lignified maize cell walls with normal monolignols (coniferyl and sinapyl alcohols) plus a series of epicatechin derivatives differing in phenolic ester substitution, each added as one-third of the precursor mixture. Cell walls were analyzed for Klason lignin and incubated in vitro with anaerobic rumen microflora to assess effects of various epicatechins on lignin formation and cell wall fermentability without pretreatment. Epicatechin or epicatechin gallate readily copolymerized with monolignols to yield cell walls with average Klason lignin concentrations of 178 mg/g, similar to lignified controls prepared with normal monolignols. By contrast, addition of epicatechin vanillate or epicatechin ferulate with monolignols depressed peroxidase activity and slightly reduced Klason lignin concentrations of cell walls to an average of 150 mg/g. Lignification with epicatechin derivatives increased the in vitro fermentability of cell walls by 4 to 27% compared to lignified controls. In ongoing work, we will assess whether incorporation of bi-phenolic epicatechin esters into lignin also facilitates the delignification and enzymatic saccharification of cell walls for fermentation into ethanol.