AOCS Approved Method
Crude fiber is determined by removing protein, sugar, starch, lipids, and parts of the carbohydrates and lignin using the organic residue remaining after microwave digestion. Samples are ground, dried, and extracted of oil. Each sample is then placed into filter bags and put into a quartz vessel with 50 mL of 0.255N H2SO4. The samples are heated to 100ºC and held at that temperature for 40 minutes in the Novawave Microwave. After rinsing in 3× DI H2O, the digestion process is repeated in the microwave with 50 mL of 0.313N NaOH. Next, after another rinse, the filter bags are immersed in acetone for 3-5 minutes and allowed to air dry. The samples are then dried in an oven at 102ºC for 2-4 hours. When samples are cool, the filter bags are placed in crucibles, weighed, and dry ashed in an oven at 485ºC for 10-12 hours. Crucibles are then reweighed and the crude fiber is calculated.
(See Method References No. 68)