The U.S. Department of Agriculture's Agricultural Marketing Service (AMS) announced a pivotal update to the U.S. Standards for Grades of Mushrooms. This final notice, published on August 25, 2026, and effective September 24, 2026, marks a substantial overhaul designed to bring federal grading standards into alignment with current industry practices and evolving market demands. The revisions aim to foster greater uniformity and consistency in commercial operations, impacting growers, packers, and consumers of fresh mushrooms.
Background to the Revisions
The impetus for these changes originated on April 2, 2020, when the American Mushroom Institute (AMI), a key trade association representing U.S. mushroom growers, retailers, and shippers, formally petitioned AMS for a comprehensive review of the existing standards. AMI highlighted a critical gap: the existing USDA standards did not adequately address contemporary industry practices. A notable deficiency was the complete absence of specific grading criteria for portabella mushrooms, a variety that has grown significantly in market presence. AMI also called for new definitions to properly categorize defects not covered by the prior standards.
Over a four-year period, from 2020 to 2024, AMS collaborated closely with AMI, providing guidance and refining the proposed revisions. This collaborative effort ensured that the eventual changes would accurately reflect the realities of modern mushroom cultivation, harvesting, and distribution. A notice and request for public comments on the proposed revisions was issued on April 10, 2026. The public response was overwhelmingly positive, with all nine submitted comments expressing support for the proposed changes.
Key Modifications to Grading Standards
The revised standards introduce several significant structural and definitional changes. At the forefront is the inclusion of portabella mushrooms within the official grading system. A new section 51.3388 establishes a "U.S. No. 1 Portabella" grade, complete with associated tolerances, formally recognizing this popular variety within federal guidelines. Previously, portabellas lacked specific federal grade classification, creating ambiguity in commercial transactions.
Another crucial adjustment is the separation of size specifications from grade criteria. Under the updated regulations, size is no longer a factor in determining a mushroom's grade. Instead, new separate sections 51.3389 and 51.3391 now exclusively address tolerances and size, respectively. This modification provides greater flexibility for packers and allows grades to focus purely on quality attributes, while size can be marketed independently.
The revisions also extensively update terminology, definitions, and defect scoring guides. The new "General" section 51.3385 clarifies that the standards apply to the Agaricus bisporus species, encompassing white button, brown button (crimini or cremini, baby, baby bella), and portabella (portobello, ports, giant crimini) mushrooms. The definition of "Damage" has been expanded to include specific defects like "Bruising," "Cuts or mechanical defects," "Discoloration," "Extraneous material," "Feathering," "Open veils," and "Spots." The previous category for "Dirt" is now subsumed under "Extraneous Material."
A notable change addresses the interpretation of "Open veils" (section 51.3392(f)). The updated definition allows for a small degree of exposed gills before they are considered damage in mushrooms other than portabellas. Crucially, "open veils" are now explicitly recognized as a characteristic of portabella mushrooms and are not considered a defect for this variety, reflecting their natural growth pattern. Furthermore, a separate tolerance for "open veils at shipping point" has been added for U.S. No. 1 grade button mushrooms (section 51.3389(a)(1)(i)).
Defect tolerances themselves have been revised for both "at shipping point" and "en route or at destination" scenarios for U.S. No. 1 and U.S. No. 2 grades, found in section 51.3389(a)(1)-(2). These adjustments reflect modern handling capabilities and reduce food waste by establishing more practical thresholds for minor imperfections.
The "Application of Tolerances" section (now 51.3390(a)-(c)) has also been revised to establish different package tolerance limits based on package size. This acknowledges the practical challenges and commercial realities of grading mushrooms packaged in various configurations.
Finally, the updated standards now explicitly permit mixed specialty packs of white and brown mushrooms. Language in the grades provisions for "U.S. No. 1" (section 51.3386), "U.S. No. 1 Portabella" (section 51.3388), and the definition of "Similar varietal characteristics" (section 51.3398) recognizes this marketing trend. When lots are not intentionally mixed, a dissimilar colored mushroom remains a defect, ensuring clarity for standard packs.
Implications for the Mushroom Industry
These revisions represent a pragmatic adaptation of federal standards to a dynamic agricultural sector. By incorporating industry feedback and acknowledging changes in production technology and consumer preferences, the USDA aims to enhance the efficiency and fairness of mushroom marketing. The introduction of specific portabella standards will provide clearer guidelines for producers, buyers, and consumers, potentially leading to more consistent product quality and pricing. The modernization of defect tolerances and the separation of size criteria offer greater operational flexibility, potentially reducing discarded product and improving supply chain efficiency. The explicit recognition of mixed specialty packs also legitimizes a growing market trend, supporting innovative product offerings from growers and retailers. Overall, these updates are expected to provide the clarity and consistency the industry seeks, fostering a more robust and adaptable market for U.S. grown mushrooms.
