Grading Corn
By Jim Lowe, Regional Director, Industry Services Division, Canadian Grain Commission, Chatham

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The process of grading corn can best be explained by breaking down the process into its component parts. Each component is important in the proper assessment of quality, and the ability to combine each of the components into an overall picture is the basis of good grading.

Sampling

This is an area where often too little time and attention are devoted, yet sampling is without doubt the most important step in the process of determining quality in a load of grain. Analysis of the sample taken will determine not only the future of that particular load of corn, but will also form the basis on which financial settlement is made or a dispute is resolved.

Good sampling techniques can be achieved in a variety of ways depending on the equipment being used. It is important to note however, that the objective of sampling, regardless of the method chosen, is to obtain a portion of the load that accurately reflects the quality of the entire package.

There are a number of sampling methods that, when performed properly, will result in a representative sample being obtained.

1. Pneumatic Probe
This hydraulic device is operator controlled and delivers the sample via a pneumatic delivery tube to a collection box, usually within the grading area. The probe is capable of reaching to the bottom of a loaded truck or wagon. Once inserted into the grain mass, the slots on the probe are opened to allow grain to fall into the probe. The grain within the probe is then transported to the collection box. Using this method, the load should be probed a number of times at various locations from front to back of the conveyance. Each probe should achieve a complete cross-section of grain from the top to bottom. The probe should not allow the sample chamber to be exposed to the vacuum airflow during the time that the probe is opened allowing grain to enter, as this may draw dockage and fine broken material into the probe and alter the representative value of the sample.

2. Hand Probe
The same methods as above are employed for manual probing.

3. Dipping
This method employs the use of a hand scoop which is used to sample grain as it is discharged from the truck or wagon. When this method is used, the entire width of the grain flow should be sampled. The process should continue until the entire load has been discharged, in order to obtain a sample reflective of the entire load.

Sample Mixing and Dividing

In all instances, a sample of a size larger than will be required should be taken. The entire sample should be thoroughly mixed and reduced to a working size (between 500 and 1000 grams) using some form of grain divider. Adjusting the working sample size by adding or removing portions by hand can alter the concentrations of fine materials in the sample and should be avoided.

Determining Dockage

The first step in the grading process is the removal and determination of the dockage content. Dockage is defined as material that can and must be removed from the sample before a final grade can be determined. In corn, the dockage procedure entails sieving the working sample over a 12/64" or 14/64" round hole sieve and then handpicking from the sieved portion, all material which is not corn (e.g. pieces of cob, other grains and large weed seeds). The sieve used for cleaning is dependent on the moisture content of the corn. The 12/64" round hole sieve is used for corn samples with a moisture of 25.0% or below. The 14/64" sieve is used for corn samples with a moisture above 25.0%. When sieving and handpicking are complete, the removed materials are weighed and expressed as a percent of the total weight of the working sample (e.g. 3.1%). This amount is deducted from the gross weight of the grain delivered. The dockage material, once removed, plays no part in the determination of the grade.

Determining Moisture Content

The Canadian Grain Commission determines moisture content in corn using the Model 919/3.5 moisture meter in conjunction with the current Grain Research Laboratory conversion charts for corn. For corn samples containing moisture up to 20.0% GRL Chart No. 6 (July 2000) is used. The test procedure is as follows:

• ensure the meter is properly calibrated;
• accurately weigh 250 grams of cleaned sample;
• determine the temperature of the grain sample using a Celsius thermometer;
• drop the sample from the load cell into the test cell ensuring no bridging occurs in the test cell. Re-drop the sample into test cell if necessary;
• determine 919/3.5 meter reading;
• locate the intersect point of temperature and meter reading from Chart #6. The intersect value is the moisture content of the sample;
• retest 2 to 3 times when moisture exceeds dry level and average results.

For corn samples above 20.0% up to 35.0%, moisture is determined using the GRL Moisture Tables 11A and 11B Quly 2000) in combination. The procedure is the same as above, with the following exceptions:

• 175 grams of cleaned sample are tested;
• a preliminary moisture value is determined from the temperature and meter reading intersect point on Table #11 A;
• the test weight in grams per 1/2 litre is determined on the cleaned sample (see determination of test weight);
• a moisture adjustment for test weight is made from Table #11B by locating the value at the intersect point of the preliminary moisture (from Table #11A) and the grams/.5 litre figure.

Test Weight Determination

Test weight is the weight of dry product in a standard unit of volume. For grains in Canada, this measurement is expressed as the number of kilograms of product contained within one hectolitre of volume (100 litres). The measurement provides an indicator of the amount of product that is available to the end-user. When combined with other factors, it can be an indicator of quality. To determine accurate test weight in corn delivered to country elevators, the following equipment is required:

• a clean sample;
• a Cox Funnel (3.81cm opening and 4.41cm drop);
• 0.5 litre measure (diameter 9cm, height 7.75cm) calibrated to hold 500ml ± 1ml of water at 20 degrees Celsius;
• a round hardwood striker (e.g. part of a broom handle);
• a grams scale.

The 0.5 L measure is filled to overflowing by hand. This grain is poured into the Cox Funnel and a single handful of additional corn is added. The Cox Funnel is placed on top of the 0.5 L pot and the flow control slide on the funnel is removed. When the funnel has emptied, it is removed without disturbing the grain in the measure. The grain is levelled with the wooden striker, using three equal zig-zag movements at a 45 degree angle. The levelled grain is poured from the measure into the scale pan and a weight in grams is determined. Test weight in corn samples containing high percentages of moisture will normally increase as the corn is dried. A table which estimates the increase in weight after drying is available from the Commission's office in Chatham. Samples where the test weight remains a factor after the increase is applied, or where a decrease in weight is suspected, should be allowed to dry before final testing.

The minimum test weight requirements are:
No. 1 C.E. 344 grams/0.5 L
No. 2 C.E. 333 grams/0.5 L
No. 3 C.E. 322 grams/0.5 L
No. 4 C.E. 311 grams/0.5 L
No. 5 C.E. 290 grams/0.5 L

Application of Grading Factors

It is impossible in an article such as this to cover adequately or describe each of the factors involved in the grading of corn. A copy of the grade schedules for corn has been included as a reference. It lists the requirements for the five quality levels in corn.

In addition, there are a number of points that relate to grading and grading procedures that producers should be aware of when delivering their grain.
- It is unlawful to deliver into commercial channels grain which has been treated with a seed treatment. The suspected presence of treated kernels is sufficient cause for rejecting a load of corn at any elevator and may result in segregation and disposal of the grain.
- Unnatural or objectionable odours in the corn will cause down-grading.
- With the exception of a few factors (e.g. stones, odour, test weight) all factors affecting quality in corn are expressed as a percentage by weight. They should not be determined on the basis of kernel counts (e.g. 1 kernel in 100 kernels = 1.0%).
- Moisture content of the corn is not a grading factor.
- There is no tolerance for insects in Canadian grains and oilseeds. The staff at the Regional Office of the Canadian Grain Commission in Chatham are available to answer your questions regarding the methods and procedures for grading corn.

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