What determines wheat quality?

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What does “quality” mean?

Wheat quality means different things to different people, depending on their perspective and their role in the wheat chain. For example, a wheat producer’s conception of what constitutes a good wheat may be radically different from the opinion of a baker working with flour. 

Quality attributes

The characteristics that impact wheat quality can be loosely categorized into two main groups. The first group of attributes is those that are inherent, i.e. under genetic control. The second group includes those characteristics influenced more by seasonal or site-specific factors. 

Inherent quality attributes

  • Protein type or quality (dough mixing tolerance, handling properties)
  • Starch properties (pasting viscosity, food texture)
  • Potential to produce grain with protein content in a specific range 
  • Grain hardness
  • Potential to produce grain with a high milling yield
  • Resistance to pre-harvest germination
  • Seed coat color

Seasonal quality attributes

  • Soundness and maturity
  • Plumpness and hence actual milling yield
  • Actual protein content
  • Weather damage
  • Content of broken, shriveled, dry green, or frosted grains
  • Contamination by foreign seeds
  • Presence of unmillable material (e.g. chaff, whiteheads)
  • Grain infestation (molds, insects)
  • Moisture content

Some of the traits listed as inherent can also be impacted by seasonal or site-specific conditions.  For instance, soil type or depth remain constant from season to season, but will still have an impact on yield or protein content.

The breeders have developed varieties tailored to specific growth environments. For the crop to demonstrate its inherent quality traits, farmers should ensure that they plant the varieties selected for their region and growing conditions.

Production factors influencing quality

Cereal quality can be impacted at a number of stages during the production process.

Seeding date – Delayed seeding may result in reduced kernel size; early seeding may result in undesirably low protein concentration and protein quality. These effects are more dramatic in areas facing water-stress.

Seeding rate – Extremely low seed rates can lead to larger grains and very high seed rates can lead to smaller grains and lower milling quality. These effects are intensified by drought, disease, and lodging.

Crop lodging – Early lodging can result in a small kernel, while later lodging will lead to kernel shriveling, and reduced test weight and milling quality. 

Nutrient supply – Whether as nutrients already in the soil or as additions of manure or fertilizer, nutrient availability and uptake will certainly impact wheat quality. 

Nitrogen application – Generally, earlier nitrogen application produces higher yields and lower protein concentration, whereas later application results in higher protein content and lower yields.
Moisture levels at time of harvest – High moisture can indicate low yields, as the maximum dry weight is not achieved. Low moisture during harvest can damage the crop through cracking and breaking.

Storage – Quality loss during storage is caused by grain deterioration, either through physical/chemical processes (i.e. high humidity) or through biological processes (i.e. pests).

Quality in terms of end-product

Because wheat differs so much from one class to the next, it is difficult to arrive at an overall definition. The quality of a wheat class is determined by its suitability for a specific final product. For instance, soft wheat is judged by its suitability for the production of cakes, cookies, or crackers. 

Hard endosperm (bread) wheats:

  • Characteristics that are important in determining the quality of a hard wheat include grain hardness, protein content, milling efficiency, and weight per volume. 
  • Even a genetically strong wheat does not necessarily indicate a good wheat by commercial bread-making standards unless it has a sufficient quantity of protein. 
  • Subnormal  bread-making properties can result from drought and heat stress (over 32°C) during the final 15 days prior to harvest.

Soft endosperm (bread) wheats:

  • With soft wheat milling, high flour yield and low protein content are considered more important than other quality traits. 
  • Grain that is closer in shape to a regular geometrical figure is more efficient than an irregularly shaped grain.
  • Soft wheat that is opaque is generally low in protein; at higher protein levels the grain can be translucent. However, the change in appearance does not affect the hardness of the kernel. 
  • Soft wheat produces a larger proportion of fine flour particles than hard wheat during milling.

Durum wheats:

  • With good quality durum wheat, the kernels are large, amber in color, translucent in appearance, with kernel size as the best indicator of potential semolina yield.
  • The test weight will generally exceed 60 lbs per bushel (or 80 kg/hl). Test weight and kernel size can vary, but will almost always exceed that of hard red spring or hard red winter wheat.
  • Semolina should be yellow in color and should be as free from specks as possible, especially when used for flat and large pasta such as lasagne, so diseased kernels are very undesirable.