Grain quality
In agriculture, grain quality judgement depends on the intended use of the grain. In ethanol production, aspects of the chemical composition of grain–and specific aspects such as starch content–are considered important. In food processing and feed manufacturing, properties such as protein, oil, and sugar are significant. In the milling industry, soundness is the most important factor. For grain farmers, high germination percentage and seed dormancy are the main features to consider. For consumers, sensory properties such as color and flavor are most important.
Properties
Overall quality of grain is affected by multiple factors, including growing practices, time and type of harvesting, post-harvest handling, storage methods, and transportation practices.The properties of grain quality can be summarized into ten main factors:
Uniform moisture content
High test weight
No foreign material
Low percentage of discolored, broken, and damaged kernels
Low breakability
High milling quality
High protein and oil content
High viability
No aflatoxin
No presence of insects and molds.
Characteristics
Grain quality is characterized according to two main types of factors: extrinsic, and intrinsic.Extrinsic factors of grain grading include age, broken grain, immature grain, foreign matter, infected grain, and moisture content.
Intrinsic factors of grain include: color, composition, bulk density, odor, size, and shape.
Color is an important primary factor for the characterization, grading, trade, and processing of grain, and is a common criterion used in the wheat trade.
Grain composition plays a significant role in the grading and marketing of grains. The main constituents of grain are: carbohydrates, protein, lipids, minerals, fiber, phytic acid, and tannins. The exact composition can vary significantly depending on the species of grain, genetics, varieties, agricultural practice, and handling of the grain.
Bulk density is defined as the ratio of the mass to a given volume of a grain sample, including the interstitial voids between the particles.
Size and shape are important factors in grain quality and grading; they vary between grain species and even between varieties of the same species. They are commonly factored into rice grading and are key factors in the milling industry.
Grade and specification
Grain grading and specification systems assure that a particular lot of grain meets the standards required by food regulation authorities, such as the Food and Drug Administration in the United States and the Food Standards Agency in the United Kingdom.In many countries, grading of grain depends on four main properties: bushel weight, moisture content, broken foreign material or the percentage fragments example broken corn foreign materials, and damaged kernels.
Test weight
Test weight, also known as volumetric weight, is one of the simplest and traditional criteria used to determine quality of grain and measure of grain bulk density. It is an indicator of general grain quality and primary grain specification; normally, a higher the test weight corresponds to higher quality, and lower test weight corresponds to lower quality, as grain quality decreases dramatically as grain deteriorates. Test weight of grain is affected by many factors, including moisture contents, frost damage, maturity, growing and harvesting conditions, drying conditions, fine material, amount of kernel damage, and grain variety.Moisture content
is defined as the quantity of water per unit mass of grain, expressed on a percentage basis. Moisture content does not directly affect grain quality, but can indirectly affect quality since grain will spoil if the moisture content is above that of the content recommended for storage.Foreign material
Broken foreign material is an important factor in grading and classification of grains. It is described as foreign material other than grains, such as sand, pieces of rock, microplastics, metals, and pieces of glass, contaminating a particular lot of grain. In the grain trade, presence of more than a set percentage of FM results in either low grades, price discount, or lot rejection, because the higher the FM the more the cost to clean before use.Damaged kernel
Damaged kernels are an important grading factor and negatively affect grain value. DK are considered those that have evident visual damage. It is usually quantified by removing damaged kernels by hand from portions free of impurities. The criteria for each grain of grade include an upper limit for the ampount of damaged kernels: for instance, for wheat to qualify as Grade 1, DK must constitute no more than 0.4% of the total weight. The majority of damage of kernels is caused by insects, heat, mold, weathering, sprouting, frost, diseases, non-uniform maturity, and/or lack of/partial grain filling.In grading systems or specification, damaged kernels are divided into two main parts: heat damaged and total damaged.
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Non-grain-standard properties
Important non-grain standards in U.S. grain standards include: breakage susceptibility, milling quality, seed viability, nutritive value, mold count and carcinogen content, and insect infestation and damage.Best example of grain quality can be described into two common grains.
Discoloration
Grain color is an important characteristic in grain grading. One common form of color deterioration is milled rice discoloration. Rice changes to different classes of milled rice discoloration if stored improperly. Rice discoloration has been shown to largely be due to microbial and chemical reactions depending on storage temperature, moisture content, and duration. Based on U.S. standard, rice will be downgraded if there is one discolored kernel per 500 gr of rice samples.Wheat
Wheat grain is the world's leading agricultural source of energy, protein and fiber; it belongs to family Gramineae and genus Triticum. Wheat grain can be categorized into three main classes: hard, soft and durum. Wheat quality can best be described in terms of end-user, nutritional quality, milling, and baking and rheology quality. In general, wheat needs to be sound, clean, well matured, and free from foreign material and damage.In general, criteria for wheat quality can be divided into three main groups: botanical, physical, and chemical characteristics.
Botanical criteria
There are two main botanical criteria: species and varieties.Physical criteria
The main physical properties that influence wheat quality are grain weight, hardness, grain size and shape, vitreousness, and color. Physical properties of grain such as wheat play a very important role in the quality of the grain, and in final products such as flour.Test weight
Test weight of wheat is considered the easiest and most common way to qualify wheat. It is an important quality factor in wheat grading as it gives rough estimates of flour yields. The basic factors that affect the test weight of wheat are kernel size and shape, kernel density, maturity of wheat, anseases and actual wheat variety.Hardness
The hardness of wheat endosperm is critical in determining the suitability of wheat for various end products and influences the processing and milling of wheat. It is the common characteristic used by millers and traders to classify wheat. In terms of hardness, wheat can be classified as either hard or soft.Color
In terms of color, wheat is classified into two classes: red wheat and white wheat. Hard red winter wheat is considered superior and commonly used for bread flour production, while white wheat is usually used for cakes, chapattis, and certain pasta noodles. Each type of wheat has different properties such as taste, baking quality and milling yields.Vitreousness
Wheat vitreousness is an optical property used by many countries to grade or quantify durum wheat quality. Based on this, wheat can be placed into three main classes: vitreous, mealy and piebald. Vitreous durum differs from non-vitreous by kernel appearance and is considered to be of better quality than non-vitreous kernels because of higher output of semolina during milling, good color and uniform coarse granulation.Chemical (quality) properties of wheat
Moisture content
Wheat grain, when harvested, typically has a moisture content of 10–12%. In most countries, moisture content is not part of the grading system, but it is the most important factor affecting the quality of wheat grain, hence is inversely related to dry matter loss. Moisture content is important in wheat quality because:- too little moisture will cause the wheat grains to break during storage and handling;
- too much moisture will facilitate the growth of mold, which results in deterioration.
Protein content
Other important qualities of wheat are milling and baking quality.
Milling quality
Most wheat is commercially sold as milled flour or semolina, hence milling quality is a crucial factor in the wheat trade. Milling depends on three main factors:- size and evenness of kernels: there is a close correlation with the weight of grain, determined by thousand-kernel weight.
- texture of the endosperm, characterized by glassiness or pearling index and hardness. They influence the utilization of energy required for milling as well as the amount of semolina obtained.
- percentage ratio of the seed-coat: the larger the kernel the lower the ratio of seed-coat, and if the layers are not thicker, then the percentage of the seed-coat will decrease too, and the color of the endosperm and seed-coat.