This test method is a procedure used to determine Acid Detergent Lignin (ADL) in feedstuffs, forages, and fibrous materials. This method measures the lignin content—a complex, indigestible component of plant cell walls—after removing other fibrous materials. Lignin is important because it negatively impacts digestibility and nutrient availability in ruminant diets. The sample is treated with an acid detergent solution using the ANKOM Fiber Analyzer to isolate ADF (cellulose, lignin, and ash). The ADF residue in ANKOM filter bags is then treated with 72% sulfuric acid, which solubilizes the cellulose, leaving lignin and ash behind. Bags are rinsed, dried, and weighed to determine the combined lignin + ash content. To isolate lignin, samples may be ashed in a muffle furnace at 550°C and reweighed. The difference gives the lignin content alone.