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United States Standards

for Grades of 

Mushrooms

Effective September 6, 2016
This issue of the United States Standards for Grades of Mushrooms (81 FR 51297) 

supersedes the previous issue which has been in effect since July 15, 1966.

Voluntary U.S. grade standards are issued under the authority of the Agricultural 

Marketing Act of 1946, which provides for the development of official U.S. grades to 

designate different levels of quality. These grade standards are available for use by 

producers, suppliers, buyers, and consumers. As in the case of other standards for 

grades of fresh and processed fruits, vegetables, and specialty crops these 

standards are designed to facilitate orderly marketing by providing a convenient 

basis for buying and selling, for establishing quality control programs, and for 

determining loan values.

The U.S. grade standards and inspection instructions for all fresh and processed fruits,

vegetables, and specialty crops are available on the internet and upon request at the 

address below. These documents provide detailed interpretations of the grade standards 

and provide step-by-step procedures for grading the product.

Grade standards are issued by the U.S. Department of Agriculture (USDA) after careful 

consideration of all data and views submitted during rulemaking. The Department 

welcomes suggestions for improving the standards in future revisions. Comments may be 

submitted to, and copies of standards and inspection instructions obtained from:

Director, Specialty Crops Inspection Division

Specialty Crops Program,

USDA, Agricultural Marketing Service

1400 Independence Avenue, SW, STOP 0240

Washington, D.C. 20250

__________________________________________________________________________

Authority: 7 U.S.C. 1621-1627.

Note: Compliance with the provisions of these standards shall not excuse failure to 

comply with the provisions of the Federal Food, Drug, and Cosmetic Act, or 

with applicable State laws and regulations.

Non-Discrimination Policy: In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights 

regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in or administering USDA 

programs are prohibited from discriminating based on race, color, national origin, religion, sex, gender identity (including gender 

expression), sexual orientation, disability, age, marital status, family/parental status, income derived from a public assistance program, 

political beliefs, or reprisal or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not all 

bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident. 

Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, 

American Sign Language, etc.) should contact the responsible Agency or USDA’s TARGET Center at (202) 720-2600 (voice and TTY) 

or contact USDA through the Federal Relay Service at (800) 877-8339. Additionally, program information may be made available in 

languages other than English. 

To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at 

http://www.ascr.usda.gov/complaint_filing_cust.html and at any USDA office or write a letter addressed to USDA and provide in the letter 

all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form 

or letter to USDA by: (1) mail: U.S. Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence 

Avenue, SW, Washington, D.C. 20250-9410; (2) fax: (202) 690-7442; or (3) email: program.intake@usda.gov. USDA is an equal 

opportunity provider, employer, and lender.
United States Standards for Grades of Mushrooms (September 6, 2016)

1

United States Standards for Grades of Mushrooms

Section Page No.

Grades............................................................................................................................ 2

§51.3385 U.S. No. 1.................................................................................................... 2

§51.3386 U.S. No. 2.................................................................................................... 2

Reserved........................................................................................................................ 3

§51.3387 Reserved. .................................................................................................... 3

Application of Tolerances ............................................................................................ 3

§51.3388 Application of tolerances.............................................................................. 3

Definitions...................................................................................................................... 3

§51.3389 Similar varietal characteristics. .................................................................... 3

§51.3390 Mature. ........................................................................................................ 3

§51.3391 Fairly well shaped........................................................................................ 4

§51.3392 Well trimmed................................................................................................ 4

§51.3393 Open veils.................................................................................................... 4

§51.3394 Spots. .......................................................................................................... 4

§51.3395 Damage....................................................................................................... 4

§51.3396 Length of stem............................................................................................. 4

§51.3397 Diameter...................................................................................................... 4

Metric Conversion Table............................................................................................... 5

§51.3398 Metric conversion table................................................................................ 5
United States Standards for Grades of Mushrooms (September 6, 2016)

2

Grades

§51.3385 U.S. No. 1.

“U.S. No. 1” consists of fresh mushrooms of similar varietal characteristics which are 

mature, at least fairly well shaped, well trimmed, free from open veils, disease, spots, 

insect injury, and decay, and from damage by any cause.

(a) Size. Size is specified in terms of diameter and unless otherwise specified 

meets the requirements of one of the following size classifications:

(1) Small to medium -- up to 1-5/8 inches in diameter;

(2) Large -- over 1-5/8 inches in diameter.

(b) Tolerances. In order to allow for variations incident to proper grading and 

handling the following tolerances, by weight, are provided as specified:

(1) At shipping point1. 5 percent for mushrooms in any lot which fail to meet 

the requirements of this grade, but not more than one-fifth of this amount 

or 1 percent shall be allowed for mushrooms affected by disease, spots, or 

decay. 

(2) En route or at destination. 10 percent for mushrooms in any lot which 

have open veils. 5 percent for mushrooms in any lot which fail to meet the 

remaining requirements of this grade, but not more than one-fifth of this 

latter amount or 1 percent shall be allowed for mushrooms affected by 

disease, spots, or decay.

(3) For off-size. Ten percent for mushrooms in any lot which fail to meet the 

specified size requirements.

§51.3386 U.S. No. 2.

“U.S. No. 2”. The requirements for this grade are the same as for U.S. No. 1 except for 

a greater tolerance for open veils and a larger tolerance for defects.

(a) Size. Size is specified in terms of diameter and unless otherwise specified 

meets the requirements of one of the following size classifications:

(1) Small to medium -- up to 1-5/8 inches in diameter;

(2) Large -- over 1-5/8 inches in diameter.

 

1 Shipping point, as used in these standards, means the point of origin of the shipment in the producing area or at port of loading for 

ship stores or overseas shipment or, in the case of shipments from outside the continental United States, the port of entry into the 

United States.
United States Standards for Grades of Mushrooms (September 6, 2016)

3

(b) Tolerances. In order to allow for variations incident to proper grading and 

handling the following tolerances, by weight, are provided as specified:

(1) At shipping point. Ten percent for mushrooms in any lot which have 

open veils. Ten percent for mushrooms in any lot which fail to meet the 

remaining requirements of this grade, but not more than one-tenth of this 

latter amount or 1 percent shall be allowed for mushrooms affected by 

disease, spots, or decay.

(2) En route or at destination. 25 percent for mushrooms in any lot which 

have open veils. 10 percent for mushrooms in any lot which fail to meet 

the remaining requirements of this grade, but not more than one-tenth of 

this latter amount or 1 percent shall be allowed for mushrooms affected by 

disease, spots, or decay.

(3) For off-size. 10 percent for mushrooms in any lot which fail to meet the 

specified size requirements.

Reserved

§51.3387 Reserved.

Application of Tolerances

§51.3388 Application of tolerances.

The contents of individual packages in the lot, based on sample inspection, are subject 

to the following limitations:

(a) For a tolerance of 10 percent or more, individual packages in any lot shall have 

not more than one and one-half times the tolerance specified: Provided, That the 

average for the entire lot is within the tolerance specified for the grade.

(b) For a tolerance of less than 10 percent, individual packages in any lot shall have 

not more than double the tolerance specified, except that at least one defective 

and one off-size specimen may be permitted in any package: Provided, That the 

average for the entire lot is within the tolerance specified for the grade.

Definitions

§51.3389 Similar varietal characteristics.

“Similar varietal characteristics” means that the mushrooms are of the same general 

color. For example, white and brown mushrooms shall not be mixed in the same 

container.

§51.3390 Mature.

“Mature” means that the mushroom is firm and well developed; the veil area may be 
United States Standards for Grades of Mushrooms (September 6, 2016)

4

stretched but not broken.

§51.3391 Fairly well shaped.

“Fairly well shaped” means that the mushroom cap is not flattened, scalloped, 

indented or otherwise deformed to an extent which materially detracts from the 

appearance or marketing quality.

§51.3392 Well trimmed.

“Well trimmed” means that the stems are smoothly cut, free from rough fleshy butts, 

the flared portion of the butt is removed and the remaining portion of the stem does not 

exceed the depth of the cap.

§51.3393 Open veils.

“Open veils” means that the cap has expanded to the extent that the protective 

covering or “veils” joining the margin of the cap to the stem have broken and exposed 

the gills or underside of the cap.

§51.3394 Spots.

“Spots” means pitted or discolored areas.

§51.3395 Damage.

“Damage” means any specific defect described in this section; or an equally 

objectionable variation of any one of these defects, any other defect, or any combination 

of defects which materially detracts from the appearance, or the edible or marketing 

quality of the individual mushroom or of the mushrooms in the lot. The following specific 

defects shall be considered as damage:

(a) Discoloration when the color of the cap or stem materially affects the appearance 

or marketing quality of the mushrooms.

(b) Dirt when any amount is embedded in the cap or stem.

§51.3396 Length of stem.

“Length of stem” means the greatest distance as measured from the point of 

attachment of the “veils” on the stem to the butt.

§51.3397 Diameter.

“Diameter” means the greatest dimension of the cap measured at right angles to the 

stem.
United States Standards for Grades of Mushrooms (September 6, 2016)

5

Metric Conversion Table

§51.3398 Metric conversion table

 

Inches Millimeters

(mm)

1/8 equals 3.2

1/4 equals 6.4

3/8 equals 9.5

1/2 equals 12.7

5/8 equals 15.9

3/4 equals 19.1

7/8 equals 22.2

1 equals 25.4

1-1/4 equals 31.8

1-1/2 equals 38.1

1-3/4 equals 44.5

2 equals 50.8

3 equals 76.2

4 equals 101.6