Inside this Issue

Page

Grain Moisture Air‐Oven Reference

Methods in the United States 1

This Month in History 1

Calendar 2

This Month in 

History

November 1, 1848 ‐ Samuel Gregory

founded the first medical school for women,

Boston Female Medical School. The first class

was 12 students. In 1874, it merged with the

Boston University School of Medicine and be‐

came the first co‐ed medical school. 

November 2, 1734 ‐ Daniel Boone (1734‐

1820) was born in Berks County, Pennsylva‐

nia.

November 6, 1860 ‐ President Abraham Lin‐

coln, the first Republican president, was

voted into office. 

November 10, 1775 ‐ The U.S. Marine Corps

was created. It was orginially part of the

Navy but became its own service branch on

July 11, 1789.

November 26, 1832 ‐ Marks the date of the

first horse‐drawn streetcar in New York City. 

November 29, 1929 ‐ American explorer

Richard Byrd completed the first airplane

flight to the South Pole.

November 29, 1832 ‐ Author Lousia May Al‐

cott (1832‐1888) was born in Philadelphia,

Pennsylvania.

1

Volume 3 Issue 6

November 19, 2012

Grain Moisture Air-Oven

Reference Methods in the

United States

Byline: G. Diane Lee

Grain moisture air‐oven reference methods are used by many stakeholders

in the United States and these reference methods play an important role in

measurement accuracy and uniformity of commercial grain moisture meter

measurements in the country. This article will provide a basic description of

the air‐oven reference methods and their use; discuss the importance of grain

moisture measurements in legal‐for‐trade applications; identify the key users

of the air‐oven reference methods for commercial use; review the origins of

these air‐oven reference methods; and outline the specific air‐oven reference

methods used for the major U.S. grains.

What are the grain moisture air-oven reference methods in the

United States and how are they used?

The grain moisture air‐oven reference methods are procedures used to de‐

termine the percent moisture content in grain. Basically, a small sample of

grain (ground or unground) that represents a larger sample set of that grain

is placed in a small metal dish and the weight of the sample is recorded. The

sample is then placed in an oven at a specific temperature and heated for a

specific amount of time. The sample is removed from the oven and cooled

in a container that prevents loss or gain of moisture during the cooling

process. Then the sample is reweighed. The loss in the sample mass is cal‐

culated as the percent moisture content of the grain. 

Commercial grain moisture meters are devices that provide a rapid prediction

of moisture in grain and are used to test the moisture of grains that are

bought and sold in the U.S. Calibrations for commercial grain moisture meters

are developed by comparing the grain moisture meter reading to grain mois‐

ture air‐oven reference values. Also, air‐oven reference methods determine

the reference moisture values of grain samples that verify the accuracy and

operation of commercial grain moisture meters. 

Why are grain moisture measurements important in commercial

(legal-for-trade) applications?

Moisture is a critical commercial measurement in grain because “discounts”

to the price per bushel of grain are made at the time of sale, based on the
Calendar 2012

Registration for training in the NIST Office of

Weights and Measures is handled by Yvonne

Branden at yvonne.branden@nist.gov.

Course descriptions can be viewed on the Office of

Weights and Measures website by clicking on the

name of the course. 

http://www.nist.gov/pml/wmd/calendar.cfm

December 3 ‐ 7 (5 days)

Administrator Workshop

Class No. 5230

NIST/Gaithersburg, MD

December 3 ‐ 7 (5 days)

Intermediate Metrology

Class No. 5164

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December 10 ‐ 14 (5 days ‐ FULL)

Handbook 133 ‐ “Checking the Net Contents of

Packaged Goods”

Class No. 5227

Raleigh, NC

2013

January 27 ‐ 30 (4 days)

NCWM Interim Meeting

Charleston, SC

Contact: info@ncwm.net

January 28 ‐ February 1 (5 days)

Volume Metrology Seminar

Class No. 5193

NIST/Gaithersburg, MD

February 25 ‐ March 1 (TENTATIVE)

Lab Administration

NIST/Gaithersburg, MD

March 4 ‐ 15 (2 weeks)

Mass Metrology Seminar

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April 4 

Webinar ‐ PT Follow‐up and RCA

April 8 ‐ 11 (4 days)

SEMAP*

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April 9 ‐ 11 (3 days)

Packaging and Labeling Seminar

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(continued on page 3)

W&M Connection 2 Volume 3 Issue 6

moisture content of the grain. “Discounts” are reductions to the price per

bushel of grain. Two examples of discounts are drying and shrinkage dis‐

counts. A grain buyer must dry grain that is too high in moisture to prevent

molding during storage. The cost associated with drying the grain or a “drying

discount” is determined based on the grain moisture measurement at the

time of sale. This discount reduces the amount of money the seller receives

for the grain. For example, a buyer may be purchasing corn from a seller at

$4.00 per bushel of corn at a target or desired 15 % moisture content. If the

seller’s corn is higher in moisture content at the time of sale than is targeted

or desired, the buyer will reduce the unit price per bushel he will give the

seller for the grain. Grains that are too high in moisture may be placed into

storage with aeration causing shrinkage. The cost associated with shrinkage

or a “shrinkage discount” is also based on the moisture of the grain at the

time of sale. Errors in the moisture measurements may result in large losses

to either the seller or buyer of grain. See article number C‐006, March 2007

“The Economic Impact of Errors in Moisture Measurements, Part 2, Grain

Moisture Meter Series,” located at:

http://www.nist.gov/pml/wmd/pubs/archives‐grain‐moisture.cfm, for addi‐

tional information on discounts. 

Who uses air-oven reference methods?

Stakeholders in the United States that use air‐oven reference methods as the

basis for commercial measurements of moisture in grain include:

• The U.S. Department of Agriculture, Grain Inspection, Packers, and

Stockyards Administration (USDA, GIPSA);

• The National Type Evaluation Program (NTEP) Laboratory for Grain

Moisture Meters;

• Grain Moisture Meter (GMM) Manufacturers; and

• State Weights and Measures and other state officials. 

These organizations work together to ensure equity in the commercial grain

market as illustrated in Figure 1, the system of commercial grain moisture

measurements in the United States and Figure 2, the movement of grain in

the United States and inspection points.

The USDA, GIPSA uses air‐oven reference methods to develop the calibrations

for the official grain moisture meter(s). These official grain moisture meters

are used to measure the moisture of grains at export locations and upon re‐

quest at interior grain facilities in the United States. 

The National Type Evaluation Program (NTEP) Laboratory at the

USDA, GIPSA uses these air‐oven reference methods when analyzing a na‐

tional grain sample set and providing manufacturers with data to develop

the calibrations for all grain moisture meters used in commercial service in

the United States. These reference methods are also used to evaluate com‐

mercial (i.e., legal for trade) grain moisture meters in the NTEP laboratory to

determine if prototypes of the device meet the requirements of the National

Institute of Standards and Technology (NIST) Handbook (HB) 44 “Specifica‐

tions, Tolerances, and Other Technical Requirements for Weighing and Meas‐

uring Devices,” prior to being used commercially in the United States. See

Figure 1, the system of commercial grain moisture measurements in the
April 15 ‐ 19 (5 days)

Fundamentals of Metrology

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NIST/Gaithersburg, MD

April 22

Webinar ‐ Management Review

April 29 ‐ May 2

Webinar ‐ Internal Auditing Best Practices (4 days)

May 6 ‐ 9

WRAP*

Class No. 5216 

Helena, MT

(continued on page 6)

W&M Connection 3 Volume 3 Issue 6

United States. 

State Weights and Measures Officials and other State Officials use

these reference methods to determine the moisture in grain samples that

are used to test commercial grain moisture meters. Typically, the grain mois‐

ture meters tested by State Weights and Measures or other state officials are

at local elevators that purchase grain from farmers in their jurisdictions. See

Figure 1, the system of commercial grain moisture measurements in the

United States and Figure 2, the movement of grain in the United States and

inspection points. 

Manufacturers of grain moisture meters use these reference air‐oven mois‐

ture methods when developing the calibrations for grain moisture meters

that they sell for use in legal‐for‐trade applications. (See Figure 1, The system

of commercial grain moisture measurements in the United States.)

Figure 1

The system of commercial grain moisture measurements in the United States.
W&M Connection 4 Volume 3 Issue 6

History of Air-oven Reference Methods in the United States

The most widely recognized reference methods for determining moisture content in grain are based on drying known

weights of grain in various types of ovens and calculating moisture content from the weight lost in the drying operation.1

The USDA, GIPSA, identifies the “air‐oven methods” as its official reference methods for determining moisture in grain and

oil seeds. According to the history of changes to USDA, GIPSA grain standards, these air‐oven reference methods have

been in use since July 1, 1935. The USDA, GIPSA air‐oven reference methods were accepted by the American Association

of Cereal Chemists (AACC, currently known as AACC International), Method 44‐15A. Although oven methods are subject

to error due to the loss of substances other than water during the drying process, Hart and Neustadt adapted the use of

Karl Fisher (KF) Titration in 1957 to test the accuracy of the USDA air‐oven moisture methods.2 The USDA air‐oven methods

were designed to give results which agree with those obtained by KF Titration. KF Titration provides moisture values by

extracting water from grain with the use of a solvent, such as methanol, and is more specific for grain moisture. Historical

records have noted that KF Titration required more time for testing than was practical and, due to the test process at that

time, there were repeatability issues from operator to operator due to portions of the test that were not automated. Frank

E. Jones and Carroll S. Brickenkamp, National Bureau of Standards (NBS, now known as the National Institute of Standards

and Technology), National Engineering Laboratory, noted that techniques were developed to automate KF Titration to ad‐

dress some of the earlier disadvantages of this method. Jones and Brickenkamp also noted that, although the KF Titration

is more specific for moisture, additional tests are needed to determine if other substances react with the solvent used to

extract water.3 The air‐oven reference methods remains the reference methods for moisture in the United States; this is

likely because these methods have been compared to KF Titration and/or other more definitive tests and have proven to

provide very repeatable measurements.

Figure 2

The movement of grain in the United States and Inspection points.
W&M Connection 5 Volume 3 Issue 6

Air-oven Reference Methods for Major U.S. Grains

There are currently eight air‐oven moisture reference methods used to determine moisture in the major U.S. grains and

these methods are recognized internationally. These reference methods vary per grain type, moisture, and commodity

and are maintained at the USDA, GIPSA in the Technology and Science Division’s Laboratory Work Instructions. These work

instructions include specific procedures, guidance on test sample size, equipment and material, and acceptance criteria

needed for each test. Because these air‐oven reference methods vary per grain type, the following tables are provided to

summarize the different air‐oven reference methods used in the United States. 

AO 1 

Single‐Stage Air‐Oven Reference Method for Moisture in Grains, Oilseeds, and Commodities is the

difference in weight after drying an ground sample of grain for one hour at 130 0C ± 1 0C (drying

time is two hours for soybean meal). The following grains and commodities are tested using this

Grains and Oilseeds Commodities

Description

Moisture

Restriction Description

Barley ≤ 16 % Barley, submitted

Lentils ≤ 16 % Bulgur

Oats ≤ 16 % Corn Soy Blend

Peas ≤ 16 % Corn Soya Flour

Rice, brown ≤ 16 % Corn Soy Milk

Rice, milled ≤ 16 % Corn, submitted

Rice, rough ≤ 16 % Corn Meal

Rye ≤ 16 % Dessert Powder

Sorghum ≤ 16 % Egg Noodles

Soybeans ≤ 10 % Hominy Grits

Sunflower ground 50/50

with celite

None (for moisture cor‐

rection of crude oil results Icing Mix Powder

Triticale ≤ 16 % Lasagna

Wheat ≤ 16 % Macaroni

Macaroni and Cheese

Rotini

Rolled Wheat

Sorghum Grits

Soybean Meal

Spaghetti

Wheat Flour

Wheat Soy Blend

Wheat Soy Milk

Wheat ‐ submitted

Cited References: AOCS Method Ba 2a-38; AACC Method 44-15A; AOAC Method 925.10; ASTM; NIST; Kenyon,

A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.
W&M Connection 6 Volume 3 Issue 6

May 6 ‐ 9

Northeatern Weights and Measures Association

(NEWMA)

Saratoga Springs, NY

Contact: James Cassidy at 

jcassidy@cambridgema.gov

May 13 ‐ 24 (2 weeks)

Mass Metrology Seminar 

NIST/Gaithersburg, MD

May 20 ‐ 23

Central Weights and Measures Association (CWMA)

Overland Park, KS

Contact: Maureen Henzler at 

maureen.henzler@kda.ks.gov

June 17

Webinar Week ‐ SOP 8, Part I 

June 17

Webinar Week ‐ Uncertainty Budgets for SOP 4

June 18

Webinar Week ‐ Management Reviews

June 18

Webinar Week ‐ SOP 8, Part II

June 19

Webinar Week ‐ SOP 18, Part I

June 19

Webinar Week ‐ Uncertainty Budgets for SOP 5

June 20

Webinar Week ‐ SOP 18, Part II

June 20

Webinar Week ‐ Undertainty Budgets for SOP 19

June 21

Webinar Week ‐ Calibration Report Evaluation

June 21

Webinar Week ‐ Uncertainty Budgets for SOP 14

July 14 ‐ 18

NCSL International

Nashville, TN ‐ Contact: info@ncsli.org

July 14 ‐ 18

NCWM Annual Conference

Louisville, KY

Contact: info@ncwm.net

July 29 ‐ August 1

Webinar ‐ Calibration Report Evaluation

(continued on page 7)

AO 2 

Two‐Stage Air‐Oven Reference Method for Moisture in Grains and Oilseeds

is the difference in weight after air‐drying a unground sample of grain until

its moisture content is 16 % ( 10 % for soybeans and 13 % for rough rice),

then drying the ground, air‐dried sample for one hour at 130 0C ± 1 0C (two

hours for soybean meal). The following grains are tested using this method:

Grains and Oilseeds

Description Moisture Restriction

Barley ≤ 16 %

Lentils ≤ 16 %

Oats ≤ 16 %

Peas ≤ 16 %

Rice, brown ≤ 16 %

Rice, milled ≤ 16 %

Rice, rough ≤ 16 %

Rye ≤ 16 %

Sorghum ≤ 16 %

Soybeans ≤ 16 %

Triticale ≤ 16 %

Wheat ≤ 16 %

Cited References: AACC Method 44-15A;, ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff,

T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO 3

Air‐Oven Reference Method for Moisture in Corn and Beans is the differ‐

ence in weight after drying an unground sample of grain for 72 hours at

103 0C ± 1 0C . The following grains are tested using this method:

Grains

Description Moisture

Corn Any

Beans Any

Cited References: AACC Method 44-15A; ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff,

T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

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g{tÇ~áz|ä|Çz
W&M Connection 7 Volume 1 Issue 1

August 5 ‐ 8

Webinar ‐ Contract Review

August 12 ‐ 15

Webinar ‐ Document Control and Recordkeeping

August 19 ‐ 23 (5 days)

Fundamentals of Metrology

NIST/Gaithersburg, MD

September 9 ‐ 12

NEMAP*

Class No. 5218

Harrisburg, PA

September 16 ‐ 19

MidMAP*

Class No. 5219

Springfield, IL

September 22 ‐ 25

Western Weights and Measures Association

(WWMA)

Kalispell, MT

Contact: Doug Deiman at 

doug.deiman@alaska.gov

September 23 ‐ 26

SWAP*

Class No. 5220

Phoenix, AZ

October 7 ‐ 9

Southern Weights and Measures Association

(SWMA)

Charleston, WV

Contact: Steve Benjamin at 

steve.benjamin@ncagr.gov

October 7 ‐ 10

Webinar ‐ Annual Submission Process*

October 21 ‐ November 1 (2 weeks)

Mass Metrology Seminar

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October 28 ‐ 31 (4 days)

Webinar ‐ Internal Auditing Best Practices

November 18 ‐ 22 (5 days)

Volume Metrology Seminar

NIST/Gaithersburg, MD

*Invitation Only

**Limited to State Laboratory Program Participants

AO 4

Air‐Oven Reference Method for Moisture in Mustard, Canola and Rape‐

seed is the difference in weight after drying an unground sample of grain

for one hour at 103 0C ± 1 0C (two hours for soybean meal), repeat the

drying and if the difference between the 1st and 2nd weight after each

drying is greater than 0.01 g the sample is dried for an additional hour.

The following grains are tested using this method:

Grains

Description Moisture

Mustard Any

Canola Any

Rapeseed Any

Cited References: ISO 665; ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995);

J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO 5 

Air‐Oven Reference Method for Moisture in Flaxseed is the difference

in weight after drying an unground sample of seed for four hours at

103 0C ± 1 0C. The following grains are tested using this method:

Grain

Description Moisture

Flaxseed Any

Cited References: AACC Method 44-15A; ASAE Method S352.2; ASTM; NIST; Kenyon,

A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111. 

AO 6 

Air‐Oven Reference Method for Moisture in Safflower seeds is the dif‐

ference in weight after drying an unground sample of seed for one hour

at 130 0C ± 1 0C. The following grain is tested using this method:

Grain

Description Moisture

Safflower Seeds Any

Cited References: ASAE Method S352.2; ASTM; NIST; Kenyon, A.S., Black, J.C., &

Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

NATIONAL CONFERENCE ON WEIGHT AND MEASURES

INTERIM MEETING

January 27 ‐ 30, 2013

Charleston, South Carolina

Addtional Information at: 

http://www.ncwm.net/content/2013‐ncwm‐interim‐meeting
W&M Connection 8 Volume 3 Issue 6

AO 7 

Air‐Oven Reference Method for Moisture in Sunflower seeds is the dif‐

ference in weight after drying an unground sample of seed for three hours

at 130 0C ± 1 0C. The following grain is tested using this method:

Grain

Description Moisture

Sunflower Seeds Any

Cited References: AOAC Method Ac 2-41; AOAC Method Ai 2-75; ASTM; NIST; Kenyon,

A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO 8 

Air‐Oven Reference Method for Moisture in Corn Gluten Feed is the dif‐

ference in weight after drying a ground sample for four hours at 103 0C

± 1 0C. The following sample is tested using this method:

Grain

Description Moisture

Corn Gluten Feed Any

Cited References: Method of the Corn Refiners Association; ASTM; NIST; Kenyon, A.S.,

Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111.

AO 10 Through AO 15 are reference methods for other commodities and

processes for laboratory check samples and equipment maintenance:

AO 10 100 0C Vacuum Oven Reference Method for moisture in Com‐

modity Samples

AO 11 Processing the Air‐Oven Laboratory Wheat Check Sample

AO 12 Processing the Air‐Oven Laboratory Corn Check Sample

AO 13 Air‐Oven Uniformity Check

AO 14 Calibrating the Thermometers Used in the Air‐Oven Laboratory 

AO 15 Moisture Dish Maintenance and Tare Weight Check Schedule

Many studies of air‐oven reference meth‐

ods have been conducted over the years

since the first use of these reference meth‐

ods. These studies resulted in changes to

the air‐oven reference methods that im‐

proved the accuracy of grain moisture

meter measurements. The air‐oven refer‐

ence methods are well established in the

U.S. Stakeholders use these reference

methods to develop the calibrations for all

commercial grain moisture meters and to

test these devices to provide uniformity in

the market place. 

NIST, OWM greatly appreciates the review

and comments of Dr. Richard Pierce, USDA,

GIPSA during the development of this arti‐

cle. 

For additional information concerning this

article, please contact Diane Lee by e‐mail

at diane.lee@nist.gov.

ENDNOTES

1, 2 Storage of Cereal Grains and Their Products,

Chapter 1: Moisture ‐ Its Significance, Behavior,

and Measurement, Haward Hunt and S.W. Pixton.

3 Journal of AOAC, Volume 64, Number 6, 1981,

Frank E. Jones and Carroll S. Brickenkamp. 

NEW PUBLICATIONS RELEASED

• Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices

(2013)

• Handbook 130, Uniform Laws and Regulations in the Areas of Legal Metrology and Engine Fuel Quality (2013)

• Handbook 133, Checking the Net Contents of Packaged Goods (2013)

Links to these publications can be found at: 

http://www.nist.gov/pml/wmd/pubs/index.cfm