Evaluation Process – Non Grade Factors


In addition to grading standards identified by governmental regulators there are often other quality measures imposed on the grain trade and millers. Tab. 11 presents a listing of non-grade evaluation criteria used for the various wheat classes. Additional flour, dough and baked or process product measurements are presented in Tab. 12 to Tab. 14. These additional factors should be considered when making wheat purchase decisions, and factors of most significance should be included in a purchase contract along with the class and grade criteria. North American milling companies conduct annual crop surveys internally or utilize outside services to evaluate the crop during the harvest. This allows their wheat buyers to identify the growing locations most closely meeting the customer's requirement. Each year's harvest produces a wheat crop with different characteristics that must be accommodated. The nature of wheat production and the commodity business often causes the wheat flour specifications used by bakers to change, depending on the crop year. Another point to consider is that a wide array of tests must be used to make an accurate evaluation. No single test has the ability to predict milling, flour, semolina or finished-product characteristics. Finally, there is the issue of the "sweat". Sweat is that period of time following harvest during which wheat milling and baking properties are less than desirable. Since wheat is a living, respiring biological material the concept of the "sweat" should be no more of a surprise than the concept of ageing beef, wine or cheese to improve flavour, aroma or texture. Once this time has passed, milling, baking and processing roperties appear more "normal". As the transition from old crop to new crop carries some economic incentive (new crop grain generally costs less), most millers and their customers agree to a managed introduction of the new crop into the mill mix to minimize any negative effect of this biological change.
Tab. 11: Wheat non-grade characteristics from 2004 a, 6
Note :
6 2004 U.S. Wheat Associates Crop Report: HRW 5-year average midwestern harvest data composite, HRS 5-year average harvest data composite, HWW harvest data pacific northwest medium protein, SRW 5-year average harvest composite, SW 5-year average pacific northwest harvest data, Durum 5-year great plains average harvest data.

Tab. 12: Wheat flour and semolina characteristics from 2004 a, 6
Tab. 13: Wheat flour and semolina dough characteristics from 2004 a, 6
Tab. 14: Wheat flour baking or semolina processing characteristics from 2004 a, 6

1. Moisture
The Grain Analysis Computer Model 2100 (GAC, 2100), manufactured by Dickey-John Corporation, Auburn, Illinois, is the official moisture meter for the national inspection and weighing system. The GAC 2100 is calibrated to the USDA air-oven method (1 h at 130 °C).

2. Protein
The standard Kjeldahl procedure for nitrogen determination used to measure protein employs a nitrogen conversion factor of N × 5.7 for wheat and flour. The exception is for feed wheat, which is determined using an N × 6.25 factor. Protein is expressed as a percentage of the sample on a 12.0% m.b. for wheat and 14.0% m.b. for flour. Protein content is a very important consideration when assessing the suitability of wheat for different end products. FGIS uses near-infrared transmittance (NIRT) spectroscopy to determine protein for official inspections. FGIS adopted the Combustion Nitrogen Analyzer in 1994 as the standard reference method for determining wheat protein because it provides accurate and consistent results with less chemical exposure to the inspectors and uses no hazardous chemicals, and the analysis time for the Combustion Nitrogen Analyzer is shorter. FGIS' wheat protein laboratory is certified ISO 9002 compliant by the International Standards Organization. All field NIRTs are calibrated to the standard protein reference method, the Combustion Nitrogen Analyzer, to ensure the accuracy of the results. Each NIRT instrument is checked for accuracy daily using a set of five standard reference samples for each class of wheat. If the daily average of the results on the standard reference samples differs by more than +/- 0.10%, the instrument is adjusted and rechecked before use. The goal is to have a daily tolerance within +/- 0.05% difference. The same set of standard reference samples is used throughout the FGIS national system for checking official NIR instruments. The Combustion Nitrogen Analyzer consists of a computer-controlled, closed system, combustion process, and a thermal conductivity detector. Protein is usually reported on the 12.0% m.b. Upon request in the sales contract, FGIS will report protein on an alternate moisture basis, in addition to the 12.0% m.b. The buyer can specify protein in the following ways:
1. Ordinary protein: any protein level can be loaded,
2. Average protein: a weighted or mathematical average of the sublots with no limit on sublot variability,
3.Minimum or maximum protein with a weighted or mathematical average of sublots where Cu-Sum7 applies with limits on sublot variability, or
4. Modified minimum or maximum protein: sublots are weighted or mathematically averaged with a reduced Cu-Sum breakpoint. For example, a request for Northern Spring wheat, minimum 14.0% protein, with no sublot below 13.8%; or Soft White wheat, maximum 9.0% protein, with no sublot above 9.2%.

Note :
7 A method of tracking variability across a large lot of grain – see Anon., 1990.

3. Wheat Ash
The ash content of wheat and flour is the mineral residue remaining after incineration of the sample. Ash is determined according to standard AACC methods and is expressed as a percentage of the sample on an 11.0% m.b. for wheat and a 14.0% m.b. for flour. Flour ash is related to the milling extraction and is used
both as a measure of flour grade and as an indication of milling efficiency.

4. Thousand Kernel Weight
Thousand-kernel weight is the weight in grams of 1,000 kernels of grain and provides a measure of grain size and density. The thousand kernel weight is independent of some factors which influence the measurement of bulk density, so it is sometimes preferred to test weight as a measure of grain quality.

5. Grain Hardness
Grain hardness is determined by measuring wheat meal granularity, expressed as the Particle Size Index (PSI). In this test, 10 g of wheat are ground in a Falling Number KT30 mill set at its finest setting. The PSI is expressed as the percentage of flour produced after 5 min sieving over a Number 15 nylon screen using a Simon Rotary sifter. Grain hardness can also be measured with a new system offered by Perten Instruments called a Single Kernel Characterization System (SKCS). The Perten Single Kernel Characterization System 4100 (SKCS 4100) provides rapid (3 min) and objective measurement of hardness classification and determin-ation of uniformity in grain. Using measurements made on 300 individual kernels in a sample, the SKCS 4100 determines individual kernel hardness, weight, diameter and moisture. Results are obtained as mean values and standard deviations for each of the four parameters. Distributions of kernel data are illustrated in histograms. Further the SKCS 4100 classifies the wheat according to the Hardness Index. Additional characteristics, such as tempering status and milling performance, can optionally be predicted.

The visual and internal quality characteristics of individual kernels of grain differ, for example between different varieties, soil types and weather conditions; the variations show, for example, in kernel hardness, moisture content, diameter and kernel weight. Within a specific load of wheat the miller wants the grain to be as uniform as possible to obtain the optimal milling result. To accomplish this, the individual
kernels need to be as uniform as possible in terms of weight, diameter, hardness, moisture etc.

6. Falling Number
The Falling Number System measures the effected α-amylase enzyme activity in grain meal to detect sprout damage and guarantee the soundness of traded grain. The principle of the Falling Number method is to use the starch contained in the sample as a substrate. The starch is rapidly gelatinized when the test tube with the sample suspended in water is inserted into a boiling water bath. Subsequently the α-amylase enzyme in the sample starts to liquefy the starch, and the speed of liquefaction is dependant on the α-amylase activity. A high level of activity causes faster liquefaction, which results in a lower Falling Number result and vice versa. The Falling Number method is used at grain intake for segregation and classification of the grain and in the flour mill for monitoring incoming grain and control of blended grain. It is also used as a basic quality parameter when grain is traded. The Falling Number system offers a rapid (approx. 10 min) way to determine the quality of the starch and α-amylase interaction. When a Falling Number test is to be performed on whole grain a hammer type laboratory mill is used to grind the grain.

7. Screenings
The wheat sample is sieved over a 2 mm slotted screen using 40 shakes of the sieve. "Screenings" is the total material passing through the screen and is expressed as a percentage by weight of the total sample.

8. Experimental Milling Evaluation
Wheat is conditioned for 24 h following the addition of an appropriate amount of water, as determined by the natural grain moisture and the PSI value. Test milling is then conducted on a Bühler laboratory mill using appropriate roller mill settings and sieve covers. The flour is usually obtained by combining all flour streams and the "straight run" flour extraction is reported. For noodle quality assessment, excluding a calculated quantity of reduction flour from the final product produces 60% extraction flour. Flour extractions are calculated on a total milled products basis.

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