Agricultural Marketing Service (AMS) has proposed updated U.S. grading standards for mushrooms following a petition from the American Mushroom Institute. The proposal, open for a 60-day public comment period until June 9, 2026, aims to modernize standards to better reflect current retail products, including formal recognition of Portabellas and Baby Bellas, which were not clearly covered under older rules.
The revised standards expand coverage to all Agaricus bisporus varieties, including white button mushrooms, brown types (Crimini/Cremini, Baby Bellas, Giant Criminis), and Portabellas (including Portobello and Ports). While the core grades (U.S. No. 1 and U.S. No. 2) remain, grading criteria are being updated. Open veils (visible gills) will no longer automatically be treated as defects for Portabellas, and limited open space is allowed for other types. Mixed packs of white and brown mushrooms will be permitted without being classified as defective.
Defect definitions : such as bruising, feathering, and mechanical damage are also being refined to reflect modern handling practices.
Size requirements are being separated from grade criteria into a dedicated section. Mushrooms will be categorized as Small (1 inch), Medium (11 5/8 inches), Large (1 5/83 inches), and Jumbo (>3 inches). Portabella size standards are adjusted to account for their naturally larger diameter.
The proposal also revises defect tolerances based on package size and distinguishes between tolerances at shipping point and after transit, recognizing that minor bruising may occur during transport.
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