Category: Post Harvest Technology

Grading is defined as segregation of heterogeneous material into series of grades reflecting different quality characteristics of significance to the users [1].  Grain right after produced and harvested in the field, is heterogeneous mixture of   Grains are graded on different basis to make good money in the market. Because it affect the price that the end users or consumers are always willing to pay. Grading system simplify trade in market by meeting the requirement of buyers and at the same time motivates producers to produce desired quality in reasonable amount.  The requirement of users widely depends on end use of the grain. For instance, low protein wheat flour is required for making cakes and muffins whereas high protein wheat flour is required for crusty bread and pizzas.

Heterogeneity of grain in a harvested lot may be due to environment conditions. For instance, the grain may be ready to harvest in some part of farm whereas in may still be immature in other part of farm. Besides, moisture content, fungal infection, discoloration, pest and insect damage mars the quality of sound grain.

Grading system:

Generally there are two type of grading system; fair and average quality system and numeric system.

Fair Average Quality System: In this system, samples are graded in such a way that it represents average quality of the grain. The consignment are distributed to purchasers with the quality near the average.

Numeric system: In this system of grading, grains are separated into divisions of quality that are defined by grading factors. Each division is identified by grade name or number. Grains are traded on the basis of these grades. This system allows buyers to obtain specific quality as desired by selecting the grade. Such grading system is practiced in United States, Canada and Australia.

Grading Factors:

Grading factors are those factors, which on failure to meet the requisite quality level will result in lower grade. There are some of the common grading factors that are applicable for cereal crops. However not all grading factors are applicable for all types of cereal grains. Examining the whole consignment for grading is impossible thing. Therefore, adequate sample is withdrawn from the parcel and grading test of grain is perform in laboratory. The collected sample is passed through seed grader to obtain homogeneous sample and to scale down our sample quantity for ease of grading.    Below are some of the commonly used grading factors [2].

1. Test weight: This is the bulk density of grain expressed in kilogram per hectoliter (Kg/hL). It is determined by specific procedures using specified equipment.
2. Varietal purity: It is the percentage of purity of variety of grains. To determine varietal purity, percentage of inferior quality grain is measured. Grain with high varietal purity is considered high quality grain without contamination of any other unintended varieties or objectionable varieties of the same grain.

3. Vitreousness: Vitreousness is the glossy or shiny appearance that indicates hardness. More vitreous the kernel, more is the protein content. The kernels that are broken, damaged, severely bleached or shows sign of starchiness fall in the category of non-vitreous kernel.

4. Soundness: Sound kernel refers to the well-developed, mature and physically undamaged grain. Soundness of kernel is determined by evaluating the extent of overall physical damage of the grain.

5. Maximum limit of foreign material: Foreign material refers to that material other than specified grain after dockage has been removed. Example of foreign material includes other cereal grains, inseparable seeds, thistle heads, heated kernels, pieces of stems, moldy grain, insect wings, rodent droppings etc. Foreign matter can be further classified as organic foreign material (OFM) and inorganic foreign material (IFM).

Factors affecting grading:

Besides the grading factors, more other things need to be considered during grading. Proper grading also requires to take account on following factors that affect grading. Sometimes they these factors are also included in grading factors as well.

1. Dockage: It is any material other than kernel of grain of standard quality that is mixed with parcel grain. Dockage must be and can be separated from the parcel of grain before that grade can be traded.

2. Moisture content: The moisture content of cleaned grain must lie within specified limit to quality to fall under certain grade. Moisture content of damp grain can be reduced either by mixing with dry grain or by drying grain again. Moisture content is important factor in grain trading as, even a small increment in moisture increases the likelihood of grain being infected by mold, insects, pests and favor germination.

3. Protein content: Globally there is high value for quality protein. Therefore, cereal grains (especially wheat) having high protein content is much valued. However, it is also matter of fact that grain with different protein content are required for different end purpose. Example; hard wheat (high protein content) is required for making bread whereas soft wheat (low protein content) is required for making biscuits and cakes.

Advantage of grading system:

1. Producer is assure for reasonable grain price relative to its quality. This also motivates farmers to produce, harvest and store grain of high quality.
2. It is easier for costumer to select their product according to their intended use.
3. Grading helps to get maximum net return from the grain for the buyers.
4. Grading facilitates trading. For globalization of trade, trade without barriers and to comply with trade agreement and treaties, grading is a must do thing.

Disadvantage of grading system:

1. The number of grades provided for each type of grain is not agreeable throughout the world.
2. Grading reduces the throughput capacity of handling and transporting system.
3. Grading requires physical separation, binning mechanism, separate storage and containment that represents overall cost to the system.
4. Sometimes, grading requires additional handling and operating cost. For instance; grain that has become damp during storage needs to be properly dried to reduce moisture content to specified level before shipping.

References:

1. Canada Grains Council (CGC). 1982. Philosophy of grading. In: Grain Grading for Efficiency and

Profit. Winnipeg, MB: Canada Grain Council, 6 p.

2. Chakraverty, A., Mujumdar, A. S., & Ramaswamy, H. S. (2003). Handbook of postharvest technology: cereals, fruits, vegetables, tea, and spices (Vol. 93). CRC press.

About Author

Name : Pratiksha Shrestha

pratiksha.shrestha2001@gmail.com

Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.