Pectin lyases, EC 4.2.2.10, are enzymes that catalyse the eliminative cleavage of methyl-esterified pectins, splitting the galacturonan chain by beta-elimination to yield unsaturated oligosaccharides. Unlike polygalacturonases they need no prior de-esterification, so they attack native pectin directly, and unlike pectate lyases they prefer the esterified substrate. Produced by many fruit-rotting fungi, they contribute to post-harvest softening and decay. In juice processing they are used to reduce viscosity and aid clarification without the methanol release that pectinesterases cause, an advantage in products where methanol levels matter. Their specificity for esterified regions makes them precise tools for modifying pectin functionality.