U Marketing and

Regulatory

Programs

Agricultural

Marketing

Service

Specialty 

Crops

Program

Specialty 

Crops 

Inspection

Division

Frozen Onions

Inspection Instructions

September 2017
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.
These instructions contain information and guidelines to help personnel of the 

U.S. Department of Agriculture’s (USDA) Specialty Crops Inspection (SCI) Division 

uniformly apply and interpret U.S. grade standards, other similar specifications, and 

special procedures.

These guidelines do not supersede the Federal Food, Drug, and Cosmetic Act or any 

other applicable Federal or State laws or regulations. Compliance with these statutes is

mandatory. This publication supersedes any previously issued inspection instructions.

The citation of any data, criteria, techniques, illustrations, copyrighted material, or 

pictorial representations accredited to private authorship is used with the permission of 

the individual(s) or source(s) cited. Unless a specific reference is cited, the information 

in this manual has been derived from sources available to the public or from the 

technical knowledge of USDA personnel.

Except for official USDA inspection aids or devices and color guides (or standards) 

produced under license of the Department of Agriculture, the mention of any supplier, 

patented device, product, brand name, or equipment does not imply endorsement by 

USDA over any other similar or equally effective material.

Inspection instructions are issued by USDA after careful consideration of all data and 

views submitted. The Department welcomes suggestions for improving the inspection 

instructions in future revisions. 

Comments may be submitted to: 

Director, Specialty Crops Inspection Division

Specialty Crops Program

USDA, Agricultural Marketing Service

1400 Independence Avenue, SW, STOP 0240 

Washington, DC 20250
THIS PAGE INTENTIONALLY LEFT BLANK
i

INSPECTION INSTRUCTIONS FOR FROZEN ONIONS

SECTION PAGE NO.

GENERAL.......................................................................................................................... 1

PRODUCT DESCRIPTION ..................................................................................................... 1

PRODUCTION FLOW ........................................................................................................... 1

INSPECTION AND GRADING ................................................................................................. 2

EQUIPMENT, INSPECTION AIDS, AND INSTRUCTIONS.............................................................. 2

SAMPLING ......................................................................................................................... 2

SAMPLE UNIT SIZE ....................................................................................................... 3

TEMPERATURE .................................................................................................................. 3

NON-QUALITY FACTORS .................................................................................................... 4

NET WEIGHT ..................................................................................................................... 4

STYLE............................................................................................................................... 4

ENZYME ACTIVITY (IF APPLICABLE)...................................................................................... 5

PREREQUISITE QUALITY FACTORS...................................................................................... 5

VARIETAL CHARACTERISTICS.............................................................................................. 5

COLOR ............................................................................................................................. 6

FLAVOR AND ODOR............................................................................................................ 6

APPEARANCE .................................................................................................................... 6

ABSENCE OF GRIT OR DIRT ................................................................................................ 7

CLASSIFIED QUALITY FACTORS .......................................................................................... 7

TABLE I ACCEPTANCE NUMBERS FOR SPECIFIED DEFECTS, WHOLE STYLE FROZEN ONION..... 8

TABLE II ACCEPTANCE NUMBERS FOR SPECIFIED DEFECTS, STRIPS, DICED OR OTHER STYLES 

FROZEN ONION ................................................................................................................. 9

DARK GREEN UNITS ........................................................................................................ 10

POOR COLORED UNITS .................................................................................................... 10

BLEMISH ......................................................................................................................... 10

MECHANICAL DAMAGE (WHOLE STYLE ONLY)...................................................................... 10

CORE MATERIAL.............................................................................................................. 10

PEEL .............................................................................................................................. 11

CHARACTER .................................................................................................................... 11

EXTRANEOUS VEGETABLE MATERIAL (EVM)...................................................................... 12
Inspection Instructions for Frozen Onions (September 2017)

1

GENERAL

The United States Standards for Grades of Frozen Onions is an Attributes standard. 

Attributes standards assign grades based on samples taken on-line (generally). No 

grade is assigned to an individual sample unit. The grade is assigned at the end of the 

production period. Attributes standards describe requirements for quality of products 

using Acceptable Quality Levels (AQLs) for lists of defects characteristic of the product. 

The defects described in the grade standard are accompanied by AQLs. Acceptance 

numbers at the AQLs given in the attributes standard would be found in sampling plan 

tables in the regulations 7 CFR 52.38b and 38c. Grading using attributes standards 

may be conducted on line while the product is being produced. As an alternative, 

samples for attributes inspection can be drawn from a lot in a storage facility or from a 

rail car, truck, or other conveyance. The minimum sample sizes are 6, 13, 21, and 29 

sample units, for attributes standards.

PRODUCT DESCRIPTION

Frozen onions are the individually quick frozen product prepared from fresh, clean, 

sound, firm bulbs of the Grano, Sweet Spanish type, or other common commercial 

varieties of (Allium cepa) that have been properly prepared, washed, blanched or 

unblanched, and then frozen in accordance with good commercial practice and 

maintained at temperatures necessary to preserve the product.

PRODUCTION FLOW

Onion Harvest

Transport

Remove Foreign Material

Wash

Sort

Blanch/Cool

Cut

Freeze
Inspection Instructions for Frozen Onions (September 2017)

2

Package

Inspect

Ship

INSPECTION AND GRADING

EQUIPMENT, INSPECTION AIDS, AND INSTRUCTIONS

• U.S. Standards for Grades of Frozen Onions

• Inspection Aid #30 series for standard and metric grids and circles

• AIM Inspection Series Manuals

o Certification Manual

o Condition of Food Container Manual

o Foreign Material Manual

o General Procedures Manual

o Safety Manual

o Sampling Manual

o Sanitation Manual

o Technical Procedures Manual

• Cumulative Sum Sampling Plan (CuSum) Attribute Standards Only

• 7 CFR 52.38b

• 7 CFR 52.38c

• SC 364-91Tally Sheet for Frozen Onions (intranet link)

• Scale

• Thermometer

• Grading tray

SAMPLING

Uniformity in the preparation and performance of sampling procedures are a 

fundamental part of Division services. Statistical sampling procedures for on-line 

inspection by attributes of processed fruits and vegetables is found in 7 CFR 52.38b. 

The Cumulative Sum Sampling Plan, referred to as ‘‘CuSum,’’ is used as the online

sampling plan for attributes standards under the following conditions.

• The producer has designated the intended grade for the basic inspection period 

prior to the start of production. 
Inspection Instructions for Frozen Onions (September 2017)

3

• Inspection of the product is be made during the basic inspection period at a point 

after which all product characteristics, subject to inspection, are fixed and will not 

be subject to change during final packaging. 

• A shift to CuSum sampling plans from lot sampling plans during a basic

inspection period is not permitted (or vice versa).

Tables VI through X contain the CuSum sampling plans for each of five different 

standard sample unit sizes. The plans within each table are listed according to 

increasing values of Acceptable Quality Levels (AQLs).

The AIM Sampling Manual section on Segregation - Attribute Type Standards provides

guidance on the procedures used when a lot of frozen onions fails during production.

Statistical sampling procedures for lot inspection of processed fruits and vegetables by 

attributes is found in 7 CFR 52.38c. Single sampling plans must be used as the lot 

sampling plan for attributes standards under either of the following conditions: 

• Sampling of the product will be made during the production period. No grade will 

be assigned to individual sample units. One grade determination only will be 

made at the end of the production period for the inspection lot. 

• Sampling of the product will be made when the inspection lot is located in a 

warehouse, truck, railroad car, or other similar conveyance.

Sample size. Samples must be randomly selected from each inspection lot in the exact 

number of sample units indicated for the lot size in tables as applicable.

SAMPLE UNIT SIZE

For varietal characteristics, color, flavor and odor, and appearance, the sample size is 

the entire container. For blemishes, character, specified defects, and mechanical 

damage, the sample size is 50 units by count for whole style, and 450 grams by weight 

for strips, diced, and other styles.

TEMPERATURE

Accurately recording the packing temperature of frozen commodities is a critical part of 

inspection. In-depth instructions on various techniques for inspecting and reporting 

temperatures may be found in the Frozen and Refrigerated Product section of the AIM 

Technical Procedures Manual.
Inspection Instructions for Frozen Onions (September 2017)

4

NON-QUALITY FACTORS

Evaluate and grade Non-quality factors on a container-by-container basis. Non-quality 

factors are not associated with the quality and condition of the commodity inspected. 

These factors speak to good commercial practices (net weight), and define the sample 

identity (style) for inspection purposes. Non-quality factors may also include technical 

procedures such as enzyme inactivation testing if requested by an applicant, or 

mandated by specification.

NET WEIGHT

Processed foods are commonly packed to meet a prescribed net weight or content, and 

are labeled accordingly. This net weight or content may be specified in a purchase 

specification or contract. In-depth instructions on performing net weights may be found 

in the Net Weight section of the AIM Technical Procedures Manual.

STYLE

The U.S. Standards for Grades of Frozen Onions cover the following styles:

• Whole style: Whole stemmed, peeled bulbs of the sizes listed below:

o Type I. 7/8 inch (22 mm) to 1-7/8 inches (48 mm) in diameter at the 

greatest dimension of the onion at right angles to a line running from stem 

to root.

o Type II (Pearl). 3/8 inch (10 mm) to 7/8 inch (22 mm) in diameter in the 

greatest dimension of the onion at right angles to a line running from stem 

to root.

• Strips: Stemmed, peeled bulbs that have been cut lengthwise into narrow 

pieces ranging from 3/4 inch (19 mm) to 2 inches (51 mm) in length. The width 

may vary from 1/4 inch (6 mm) to 3/4 inch (19 mm).

• Diced: Peeled bulbs which have been cut into approximately square pieces with 

a designated width ranging from 1/4 inch (6 mm) to 1 inch (25 mm) in width as 

determined by the width of the unit in the greatest cut dimension.

• Other: Any style designated as other, by style, description of size, shape, or 

other characteristic that differentiates it from the styles listed above.
Inspection Instructions for Frozen Onions (September 2017)

5

The requirements for style are determined by count or weight as follows:

• Whole Style

o Type I. The units are well shaped. By count, approximately 10 percent of 

the units (lot average) may be less than 7/8 inch (22 mm); 5 percent may 

be greater than 1-7/8 inches (48 mm) at the widest portion of the unit.

o Type II (Pearl). The units are well shaped. By count, approximately 10 

percent of the units (lot average) may be less than 3/8 inch (10 mm); 5 

percent may be greater than 7/8 inch (22 mm) in the greatest portion of 

the unit.

• Strips style. A maximum of 25 percent of units, by weight, may be less than the 

minimum style requirement of 3/4 inch (19 mm) in length.

• Diced style. The units that are practically uniform in size. Less than 30 percent 

of the units, by weight, are noticeably smaller than one-half the area of an 

average sized unit (or the designated size). Less than 30 percent of all units are 

large or irregularly shaped units greater than 1-1/2 times the area of an average 

sized unit (or the designated size).

• Other. Units do not fall into any of the styles listed above, are reasonably 

uniform in size and shape, and overall appearance is not materially affected by 

other shapes and sizes.

ENZYME ACTIVITY (IF APPLICABLE)

Frozen onions are not routinely tested for enzyme inactivation by inspection staff. If 

required by a specification, or requested by the applicant, enzyme inactivation 

inspection will be performed using the guidance found in the Enzyme Inactivation 

section of the AIM Technical Procedures Manual.

PREREQUISITE QUALITY FACTORS

Evaluate and grade prerequisite quality factors on a container-by-container basis. 

Prerequisite quality factors are typically inspected using subjective analysis of specific 

quality factors. 

VARIETAL CHARACTERISTICS

• Similar should be assigned to samples containing frozen onions of similar 

varietal characteristics.
Inspection Instructions for Frozen Onions (September 2017)

6

• SSTD should be assigned to samples containing frozen onions of dissimilar 

varietal characteristics. See the Alien Vegetables section of the AIM General 

Procedures manual for additional guidance and allowances.

COLOR

Color is evaluated immediately upon thawing as frozen products tend to oxidize rapidly 

after thawing, and may effect this determination.

Color refers to the predominant and characteristic color of the exterior surface of the 

frozen onions.

• Good color: The frozen onions have a good characteristic bright color typical of 

the variety.

• Reasonably good color: The frozen onions have a reasonably good color 

typical of the variety. The units individually or collectively may vary slightly from 

bright to slightly dull.

• Poor color: The frozen onions fail to meet the requirements of reasonably good 

color.

Any poor colored units found during this analysis are counted or weighed (depending on 

style), and recorded under Poor Colored Units as part of the classified quality factor 

evaluation.

FLAVOR AND ODOR

Flavor and odor are determined before and after cooking. Cooking procedures are 

found in the Frozen and Refrigerated Product section, Cooking Procedures subsection 

of the AIM Technical Procedures manual. All frozen sample units must be cooked for 

flavor and odor evaluation.

• Normal flavor and odor: The frozen onions, before and after cooking, have a 

flavor and odor that is normal and typical for the variety and is free from 

objectionable flavors and odors.

• Off flavor and odor: The frozen onions do not meet the requirements for 

normal flavor and odor listed above.

APPEARANCE

Appearance of frozen onions is based on the overall appearance before thawing (free 

flowing), and immediately after thawing (brightness, uniformity of appearance). The 

factors for appearance include:
Inspection Instructions for Frozen Onions (September 2017)

7

• Free flowing: The individual units in the frozen state are not stuck to one 

another, stuck together in blocks, to an extent that they cannot easily be 

separated in a frozen state.

• Brightness: The onions are bright in color and not affected by dullness. 

Brightness is evaluated immediately after thawing. 

• Uniformity of size: The variation in size of the whole onion, or uniformity of cut 

size for strips, diced, or other.

Record appearance as follows:

• Good appearance: The product is practically free flowing, bright, and with 

practically uniform units. Markedly variable units, small specks, or other factors, 

do not significantly affect the overall appearance or edibility of frozen onions.

• Reasonably good appearance: The product is reasonably free flowing, 

reasonably bright, and has reasonably uniform units. The overall appearance or 

edibility of the frozen onions is slightly but not seriously affected by markedly 

variable units, small specks, or other factors.

• Poor appearance: The product fails to meet the requirements of reasonably 

good appearance.

ABSENCE OF GRIT OR DIRT

Evaluation for grit or dirt is performed during organoleptic evaluation for flavor and 

during all visual inspection performed, including a visual analysis of the water remaining 

after cooking the frozen onions for flavor and odor.

There is no allowance for grit or dirt. The presence of grit or dirt during organoleptic 

evaluation, or any visual observance would render the sample SSTD.

Record absence of grit or dirt as None. 

CLASSIFIED QUALITY FACTORS

Classified quality factors are quantified by count and weight with allowances specified in 

the U.S Standards for Grades of Frozen Onions, §52.4078, Requirements for classified 

quality factors and defects, Tables I and II.
Inspection Instructions for Frozen Onions (September 2017)

8

TABLE I ACCEPTANCE NUMBERS FOR SPECIFIED DEFECTS, WHOLE STYLE 

FROZEN ONION 

GRADE A (50 Plan)

GRADE B (50 Plan)

 1 Unofficial Samples

2 AQL calculated from tolerance (TOL) at 650 units

Sample Units X Sample Unit Size 1 x 50 6 x 50 13 x 50 21 x 50 29 x 50

Units of Product 50 1 300 650 1050 1450

DEFECTS TOL AQL2 ACCEPTANCE NUMBERS

Dark Green Units 1 0.612 1 4 7 10 14

Poor Color Units 5 3.8 4 17 33 50 67

Major Blemish 2 1.3 2 7 13 20 26

Total Blemish (Major + Minor) 5 3.8 4 17 33 50 67

Mechanical Damage 2 1.3 2 7 13 20 26

Major Core Material 1 0.612 1 4 7 10 14

Total Core Material (Major + Minor) 2 1.3 2 7 13 20 26

Peel 2 1.3 2 7 13 20 26

Character “Reasonably Good” 2 1.3 2 7 13 20 26

Character “Poor” 1 0.612 1 4 7 10 14

EVM 1 0.612 1 4 7 10 14

Sample Units X Sample Unit Size 1 x 50 6 x 50 13 x 50 21 x 50 29 x 50

Units of Product 50 1 300 650 1050 1450

DEFECTS TOL AQL2 ACCEPTANCE NUMBERS

Dark Green Units 2 1.3 2 7 13 20 26

Poor Color Units 8 6.4 6 26 52 80 108

Major Blemish 3 2.9 3 13 26 39 53

Total Blemish (major + minor) 8 6.4 6 26 52 80 108

Mechanical Damage 3 2.9 3 13 26 39 53

Major Core Material 2 1.3 2 7 13 20 26

Total Core Material (major + minor) 3 2.9 3 13 26 39 53

Peel 3 2.9 3 13 26 39 53

Character “Poor” 2 1.3 2 7 13 20 26

EVM 2 1.3 2 7 13 20 26
Inspection Instructions for Frozen Onions (September 2017)

9

TABLE II ACCEPTANCE NUMBERS FOR SPECIFIED DEFECTS, STRIPS, DICED OR 

OTHER STYLES FROZEN ONION

GRADE A (450 Gram Plan)

 3 Unofficial Sample

4 AQL calculated from tolerance (TOL) at 5850 units

Sample Units X Sample Unit Size 1 x 450 6 x 450 13 x 450 21 x 450 29 x 450

Total Weight of Product (in grams) 450 3 2700 5850 9450 13050

DEFECTS TOL AQL4 ACCEPTANCE NUMBERS

Dark Green Units 0.11 0.056 1 3 6 9 12

Poor Color Units 0.88 0.696 6 26 51 79 106

Major Blemish 0.22 0.144 2 7 13 19 26

Total Blemish (major + minor) 0.88 0.696 6 26 51 79 106

Major Core Material 0.11 0.056 1 3 6 9 12

Total Core Material (major + minor) 0.44 0.325 3 13 26 40 53

Peel 0.22 0.144 2 7 13 19 26

Character “Reasonably Good” 1.0 0.9 7 32 64 100 135

Character “Poor” 0.5 0.4 4 16 31 48 64

EVM 0.11 0.056 1 3 6 9 12

GRADE B (450 Gram Plan)

Sample Units X Sample Unit Size 1 x 450 6 x 450 13 x 450 21 x 450 29 x 450

Total Weight of Product ( in grams) 450 3 2700 5850 9450 13050

DEFECTS TOL AQL 4 ACCEPTANCE NUMBERS

Dark Green Units 0.22 0.144 2 7 13 19 26

Poor Color Units 2.0 1.72 12 57 117 183 249

Major Blemish 0.67 1.72 5 20 39 60 81

Total Blemish (major + minor) 2.0 1.72 12 57 117 183 249

Major Core Material 0.22 0.144 2 7 13 19 26

Total Core Material (major + minor) 0.88 0.696 6 26 51 79 106

Peel 0.22 0.144 2 7 13 19 26

Character “Poor” 4.0 3.6 23 113 234 370 506

EVM 0.22 0.144 2 7 13 19 26
Inspection Instructions for Frozen Onions (September 2017)

10

DARK GREEN UNITS

Dark green units are units with dark green stripes across 50 percent or more of the 

onion unit. Any amount that reaches or exceeds 50 percent of the visible area is 

considered one unit. One unit is equivalent to one defect for all styles. 

POOR COLORED UNITS

Color in frozen onions is part of the prerequisite quality evaluation. Any poor colored 

units found during this analysis are counted or weighed (depending on style), and 

recorded as part of the classified quality factor evaluation.

BLEMISH

Any unit that is affected or damaged by pathological injury, insect injury, or any other 

injury that affects the overall appearance or eating quality of the unit.

To perform this analysis use inspection aid 30 series measurement guides with either 

metric or standard circles.

• Major blemish: Any unit with tan to dark blemish(es) that, in the aggregate, are 

larger than the area of a circle 1/4 inch (6 mm) in diameter.

• Minor blemish: Any unit with tan to brown blemish(es) that, in the aggregate, 

are larger than the area of a circle 1/8 inch (3 mm) in diameter but smaller than 

1/4 inch (6 mm) in diameter.

• Total blemish: The combined total of major and minor blemishes.

MECHANICAL DAMAGE (WHOLE STYLE ONLY)

Mechanical damage means that the appearance of the unit is affected by gouging, or 

the unit is crushed or broken by mechanical means to the extent that the appearance is 

materially affected. 

CORE MATERIAL

Core material is the portion of the onion bulb that is part of the internal or external onion 

flesh. This material should not be discolored, excessively tough, fibrous, soft, or mushy. 

Core material may also include sprouts, seed stems, root crown, and root material.

To perform this analysis use inspection aid 30 series measurement guides with either 

metric or standard grids.
Inspection Instructions for Frozen Onions (September 2017)

11

• Major Core Material

o In whole style: Major core material is a unit that is more than 3/8 inch 

(10mm) in diameter or length, whichever is applicable. Each unit is the 

equivalent of one major defect.

o In strips, diced, and other styles: Major core material exceeds 1/2 

square inch (3.2 square centimeters). Each unit is the equivalent of one 

major defect.

• Minor Core Material

o In whole style: Minor core material is a unit that is 3/8 inch (10mm) or 

less in diameter or length, whichever is applicable. Each unit is the 

equivalent of one minor defect.

o In strips, diced, and other styles: Minor core material is 1/2 square inch 

(3.2 square centimeters) or less. Each unit is the equivalent of one minor 

defect.

• Total core material: The combined total of major and minor core material.

PEEL

Peel is the thin outer skin of the bulb. Peel is usually creamy white to brown in color, 

tough, and tissue-like. Each equivalent of peel that is 1/2 square inch (3.2 square 

centimeters) is considered one defect.

To perform this analysis use inspection aid 30 series measurement guides with either 

metric or standard grids.

CHARACTER

The analysis for character is performed on thawed product. Character refers to the 

firmness and texture of the individual onion unit and the lack of tough, soft, or mushy 

units.

• Good character: The onions are uniformly firm and tender, and practically free 

of soft and spongy units.

• Reasonably good character: The onions are reasonably firm and tender, and 

are not soft or spongy.

• Poor character: The product fails to meet the requirements of reasonably good 

character.
Inspection Instructions for Frozen Onions (September 2017)

12

EXTRANEOUS VEGETABLE MATERIAL (EVM)

EVM is any plant material of onions or other harmless plants including, but not limited 

to, the leaves or roots. Each equivalent of EVM of 1 inch in length is considered one 

defect in any style of frozen onion.

To perform this analysis use inspection aid 30 series measurement guides with either 

metric or standard grids, or a ruler as applicable.