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United States Standards

for Grades of

Mushrooms for Processing

Effective April 1, 1964

(Reprinted - January 1997)
 These standards apply only to the cultivated mushroom Agaricus Campestris. 1

 NOTE: Packing of the product in conformity with the requirements 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.

1

United States Standards for Grades of Mushrooms for Processing 1

Grades

51.3435 U.S. No. 1.

51.3436 U.S. No. 2.

Culls

51.3437 Culls.

Cull Material

51.3438 Cull material.

Definitions

51.3439 Similar varietal characteristics.

51.3440 Fairly well shaped.

51.3441 Tender.

51.3442 Soft.

51.3443 Mushroom cap.

51.3444 Whole mushroom. 

51.3445 Usable piece. 

51.3446 Usable portion of stem. 

51.3447 Damage. 

51.3448 Serious damage. 

51.3449 Diameter. 

Grades 

§51.3435 U.S. No. 1. 

"U.S. No. 1" consists of fresh mushroom caps or, when so specified, whole mushrooms of similar

varietal characteristics which are not soft, which are at least fairly well shaped, tender, and are

free from decay, disease spots and insects and free from damage caused by insects, bruising,

discoloration, feathering or other means. 

(a) Size: Unless otherwise specified, each mushroom cap is not less than one-half inch in diameter. 

§51.3436 U.S. No. 2. 

"U.S. No. 2" consists of fresh mushroom caps, whole mushrooms, usable pieces, and the usable

portions of the stems of mushrooms of similar varietal characteristics which are tender, are free

from decay and insects and free from damage caused by insects and free from serious damage

caused by disease spots, bruising, discoloration, feathering or other means. 

(a) Size: Unless otherwise specified, each mushroom cap is not less than one-half inch in diameter. 
2

Culls 

§51.3437 Culls. 

"Culls" consist of fresh whole mushrooms, mushroom caps, pieces and stems of mushrooms

which fail to meet the requirements of the U.S. No. 2 grade. 

Cull Material 

§51.3438 Cull material. 

"Cull material" means the root end of the stem with or without adhering caked dirt, loose dirt and

other foreign material or extraneous material. 

Definitions 

§51.3439 Similar varietal characteristics. 

"Similar varietal characteristics" means that the mushrooms are of the same general color. Those

of white color shall not be mixed in the same container with cream or brown mushrooms. 

§51.3440 Fairly well shaped. 

"Fairly well shaped" means that the mushroom cap is not flattened, scalloped, indented or

otherwise deformed to an extent that materially detracts from the appearance or the processing

quality. 

§51.3441 Tender. 

"Tender" means the flesh of the cap and stem is not fibrous, rubbery or stringy. 

§51.3442 Soft. 

"Soft" means that the mushroom cap is more than slightly indented or concave; or the veil is

stretched or open and has a cottony appearance. 

§51.3443 Mushroom cap. 

"Mushroom cap" means the round crown or top part of the mushroom, which may include a

relatively short portion of the stem. 

§51.3444 Whole mushroom. 

"Whole mushroom" means the mushroom cap with the usable portion of the stem attached. 

§51.3445 Usable piece. 

"Usable piece" means a piece of cap or stem which is not seriously damaged. 

§51.3446 Usable portion of stem. 

"Usable portion of stem" consists of that portion of the stem remaining after the cap and root end

have been removed. 

§51.3447 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 edible or processing quality of the mushrooms. The following specific defects

shall be considered damage: 

(a) Bruising, when more than 5 percent of the surface of the mushroom cap is materially flattened,

ragged or skinned; 

(b) Discoloration, when more than 5 percent of the aggregate surface of the mushroom cap is

affected by discoloration which distinctly contrasts with the normal color of the mushroom; 

(c) Mushrooms showing evidence of insect feeding; and, 

(d) Feathering, when materially affecting the appearance of white mushroom caps and when raised

and affecting more than 5 percent of the surface of cream or brown mushroom caps. 
3

§51.3448 Serious damage. 

"Serious 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

renders the mushroom cap, whole mushroom or detached stem unsuitable for processing. The

following specific defects shall be considered as serious damage: 

(a) Bruising, when more than 20 percent of the surface of the mushroom cap is distinctly

flattened, ragged or skinned; 

(b) Discoloration, when more than 20 percent of the aggregate surface of the mushroom cap is

badly discolored; 

(c) Disease spots, when affecting more than 10 percent of the cap surface; and, 

(d) Feathering, when hard, rough separations of the flesh affect more than 20 percent of the

surface of cream or brown mushroom caps. 

§51.3449 Diameter. 

"Diameter" means the greatest dimension of the cap measured at right angles to the stem.