This work demonstrates that the biosurfactant produced by Lactobacillus pentosus from grape marc hydrolysates can be successfully employed in reducing the water repellence of hydrophobic substrates, rather than chemical surfactants, as it can be produced from low-cost residual materials and it is less toxic than chemical surfactants. The method employed to measure the water repellence of the 11 plant substrates, consisting of pine bark, peat, and composts from various origins (biodegradable fraction of municipal solid waste, green waste, sewage sludge, manure, pine bark, and grape marc), was the molarity of ethanol droplet method (MED). Peat, pine bark, and the composts obtained from grape marc and pine bark were severely hydrophobic, having contact angles over 104 degrees , whereas the composts from municipal solid waste were less hydrophobic, with contact angles under 101 degrees . When hydrophobic substrates were treated with the biosurfactant from L. pentosus, the water repellence of the plant substrates was reduced in all but two cases (the least hydrophobic composts), achieving in most of the cases results better than those obtained using chemical surfactants.