NOVELTY - A solid and fibrous product is extracted from embedding natural matrices of plant based raw materials by removing the aqueous liquor containing soluble extracts of the embedding matrices; passing the aqueous liquor through an anaerobic reactor where the soluble extracts are gasified and removed as a methane rich gas at biological conditions of 10-50 degrees C and pH of 4-8; and returning the liquor for contacting with the raw materials and repeating the process until product is detached from the embedding matrices.    USE - Process of extracting a solid and fibrous product from embedding natural matrices of plant based raw materials (claimed) for making white pepper.    ADVANTAGE - The process provides a clean extraction of plant materials, removes pollutants generated in the biological extraction of plant materials, generates biogas as a fuel from the pollutants in the extraction water, shortens the time required for the extraction of plant materials, reuses water for the extraction plant materials, and provides fast removal of skins of dried black or fresh pepper berries for making white pepper while the pollutants are converted into gases and removed.    DETAILED DESCRIPTION - A solid and fibrous product is extracted from embedding natural matrices of plant based raw materials by:    (A) soft crushing the plant materials for easy liquid passage for extraction of fiber;    (B) contacting the crushed raw material with an aqueous liquor from an anaerobic system containing microbial sludge as well as anaerobic sludge capable of depolymerization and solubilization of the embedding matrices;    (C) removing the aqueous liquor containing soluble extracts of the embedding matrices;    (D) passing the aqueous liquor through an anaerobic reactor where the soluble extracts are gasified and removed as a methane rich gas at biological conditions of 10-50 degrees C and pH of 4-8; and    (E) returning the liquor for contacting with the raw materials and repeating the process until product is detached from the embedding matrices.