What The Tests Mean
Wheat Grade Tests
Wheat Grade Tests reflect the physical quality and condition of a sample and thus may indicate the general suitability for milling. The U.S. grade for a sample is determined by measurement of such factors as test weight, damaged kernels, foreign material, shrunken and broken kernels and wheat of contrasting classes. All numeric factors other than test weight are reported as a percentage by weight of the sample. Grade determining factors include:
- Total Defects is the sum of damaged kernels, foreign material and shrunken and broken kernels.
- Test Weight is a measure of the density of the sample and may be an indicator of milling yield and the general condition of the sample, as problems during growing season or at harvest often reduce test weight.
- Damaged Kernels are kernels which may be undesirable for milling because of disease, insect activity, frost or sprout damage, etc.
- Foreign Material is any material other than wheat that remains after dockage is removed. Because foreign material may not be removed by normal cleaning equipment, it may have an adverse effect on milling and flour quality.
- Shrunken and Broken Kernels are kernels that were insufficiently filled during growing and have a shrunken or shriveled appearance or were broken in handling. Such kernels may reduce milling yield.
- Vitreous Kernels in hard red spring wheat are kernels that are uniformly dark and have no spots that appear chalky or soft. In durum, vitreous kernels have a glassy and translucent appearance without any spots that appear chalky.
Wheat Non-Grade Tests
Dockage is the percentage by weight of any material easily removed from a wheat sample using the Carter Dockage Tester. Dockage, because it can be removed, should not have any affect on milling quality but may have other economic effects for buyers. Grade factors are determined only after dockage is removed.
Moisture content is the percentage of water by weight of a sample and is an important indicator of profitability in milling. Flour millers add water to adjust wheat moisture to a standard level before milling. Lower wheat moisture allows more water to be added, increasing the weight of grain to be milled at virtually no cost. Moisture content is also an indicator of grain storability as wheat and flour with low moisture are more stable during storage. Because moisture can be readily added to or physically removed from a sample, other analysis results are often mathematically converted to a standard moisture basis (mb), such as 14%, 12% or dry matter, so results can be compared.
Protein content is the percentage of protein by weight in a sample. Protein can be quickly and easily measured and therefore is an important factor in determining the value of wheat since it relates to many processing properties, such as water absorption and gluten strength. Low protein is desired for products such as snacks or cakes. High protein is desired for products such as pan breads, pasta, buns and frozen yeast-raised products.
Ash content is the percentage of minerals by weight in wheat or flour. In wheat, ash is primarily concentrated in the bran and is an indication of the flour yield that can be expected during milling. In flour, ash content indicates milling performance by indirectly revealing the amount of bran contamination in flour. Ash in flour can impart a darker color to finished products. Products requiring white flour call for low ash content, while whole wheat flour has higher ash content.
1000 Kernel Weight is the weight in grams of one thousand kernels of wheat and may indicate grain size and expected milling yield.
Kernel Size is a measure of the percentage by weight of large, medium and small kernels in a sample. Large kernels or a more uniform kernel size may help improve milling yield.
Single Kernel Characterization System (SKCS) measures 300 individual kernels from a sample for size (diameter), weight, hardness (based on the force needed to crush) and moisture. Detailed SKCS results (not reported in this booklet) include the distribution of these factors, which may be an indicator of the uniformity of the sample and help millers experienced with the system optimize flour milling yields. Kernel characteristics are related to milling properties such as tempering, roll gap settings and flour starch damage content.
Sedimentation value is a measure of the sediment that results when lactic acid is added to a sifted ground wheat sample and can be used as an indicator of gluten quality and thus the baking quality of wheat flour.
Falling Number indirectly indicates alpha-amylase activity, which results from sprout damage. High falling number values indicate low alpha-amylase activity. Sufficient alpha-amylase activity is required in flour for some products such as yeast-raised bread. However, excessive alpha-amylase in wheat cannot be removed and it is difficult to blend to a lower alpha-amylase content. The resulting flour produces a sticky dough that can cause problems during processing and products with poor color and weak texture. Falling number usually correlates closely with amylograph.
DON (deoxynivalenol) is a mycotoxin produced by fusarium fungi in grain.
Extraction is the percentage by weight of flour obtained from a wheat sample. In a commercial flour mill, the extraction rate is critically important to mill profitability. In a laboratory, milling with the Buhler Laboratory mill is mainly done to obtain flour for other tests. The Buhler Laboratory mill extraction rate is always significantly lower than the rate that can be obtained on a commercial mill, but may be useful for comparison between crop years.
Wet Gluten is a measure of the quantity of gluten in wheat or flour samples as determined using the Glutomatic system. Gluten forms when water is added to the protein in wheat and is responsible for the elasticity and extensibility characteristics of flour dough.
Gluten Index is also determined by the Glutomatic system and is a measure of gluten strength regardless of the quantity of gluten present. Gluten index is used commercially to select durum samples with strong gluten characteristics. In bread wheat, a variety of factors other than gluten quality can affect the results though very low gluten index may be an indication of protein damage from insect or disease activity.
Amylograph measures flour starch pasting properties that are important to end products such as sheeted Asian noodles. Amylograph also measures enzyme (alpha-amylase) activity which results from sprout damage. Amylograph results usually correlate closely with falling number results.
Starch damage is the percentage by weight of damaged starch in a flour sample, which is a measure of the physical damage done to starch granules during milling. Bread (hard) wheat flour typically has higher starch damage than soft wheat flour. Highly damaged starch readily absorbs more water, which affects dough mixing and other processing properties. Because starch damage depends on how the sample was milled, starch damage is important for interpreting other results reported.
Solvent Retention Capacity (SRC) is the weight of solvent held by flour after centrifugation, expressed as a percent of the flour weight on a 14% mb. The results can be useful for predicting commercial baking performance, especially for low protein soft wheat flours. The different solvents used relate to the functionality of specific flour components as follows:
- Water — Water absorption
- Sucrose — Pentosans
- Lactic Acid — Glutenins
- Sodium Carbonate — Damaged starch
- Gluten Performance Index (GPI) — is defined as a ratio of three of the SRC values, lactic acid/(sodium carbonate + sucrose), and is a good predictor of overall performance of flour glutenins, especially for bread wheat flour.
Color is a numerical system to measure a sample’s lightness (L*) on a scale of 0 to 100 and “chromaticity” or hue on two scales each running from -60 to +60 for green-red (a*) and blue-yellow (b*). High L* values indicate a bright color, and higher b* values indicate more yellow. Flour color is influenced by the wheat’s endosperm color particle size and the ash content of the flour and often affects the color of the finished product. Durum semolina color is heavily influenced by particle size.
Evaluation of end-products
- Baking Absorption is the water required for optimum dough mixing performance, expressed as a percent of flour weight on a 14% mb.
- Crumb Grain and texture is determined on a scale of 1 to 10 by visual comparison to a standard using a constant illumination source. Higher scores are preferred.
- Loaf Volume is the volume of the test loaf after baking. Higher loaf volumes indicate better baking performance for pan breads.
- Specks are small particles of bran or other material that escaped the wheat cleaning and semolina purifying process and thus depend on the milling process as well as the characteristics of the durum. Specks, which can detract from pasta appearance and desirability, are visually counted in a semolina sample and reported as the number in 10 square centimeters.
- Sugar Snap Cookie, Sponge Cake, Chinese Southern-Type Steamed Bread, Spaghetti, and hard white (HW) noodle and steamed bread tests all use standardized methods to prepare specific end products to evaluate the suitability of the sample for that product or similar products. Details on many of these tests can be found in the Analysis Methods section of this booklet.
Farinograph generates a curve that indicates the power used over time as flour and water are mixed into dough. The results describe the mixing properties of the dough and include:
- Peak Time is the time interval from the first addition of water to the maximum consistency immediately prior to the first indication of weakening. Long peak times indicate strong gluten and dough properties while short peak times may indicate weak gluten.
- Stability is the interval between the point where the top of the curve first intersects the 500-BU line (called the “arrival time”) and the point where the top of the curve departs the 500-BU line (“departure time”). Long stability times also indicate strong gluten and dough properties, useful in products such as yeast-raised breads while short stability times indicate weaker gluten useful in many confectionary products.
- Absorption is the amount of water (as a percent by weight of 14% moisture wheat flour) required to center the curve peak on the 500-BU line. High water absorption in hard wheat flour provides economic advantages for producing more dough pieces than flour with lower water absorption. Lower water absorption is preferred for cookie and cracker products with soft wheat flour.
Extensograph generates a force-time curve for a piece of dough stretched until it breaks. Results include:
- Maximum Resistance, measured at the maximum curve height in Brabender units (BU), reflects the maximum force applied and indicates the resistance of the dough to extension.
- Extensibility, measured as the total length of the curve at the base line in centimeters, reflects how far the dough was stretched until it breaks.
- Area is the area under the curve reported in square centimeters.
These factors help describe the gluten strength and dough extensibility characteristics of flour for a wide range of end products. The extensograph can also evaluate the effects of fermentation time and additives on dough performance.
Mixograph generates a graph that records the force needed to mix flour or semolina and water into dough. The mixograph is similar to the farinograph but is quicker and uses a pin mixer and a smaller flour sample. Peak height and peak time are common mixing parameters that are determined from mixogram.
- Classification indicates dough characteristics for durum milled fractions on a scale of 1 to 8 with higher values indicating stronger dough properties.
- Peak Time is the interval from the first addition of water to when the curve peaks and is considered an indicator of both the rate of dough development and hydration rate. Short peak time indicates a quick hydration rate and long peak time a slow hydration rate.
- Peak Height is the height of the curve at peak time measured from the bottom of the mixogram paper to the middle of the band width at the curve peak. Peak height is primarily a function of protein content, but is affected by water absorption and dough strength. Peak height increases with protein content and dough strength, decreases with water absorption and is measured in “Mixograph units (MU)”. An MU is one rectangle on the mixogram.
Alveograph generates a curve indicating the air pressure necessary to inflate a piece of dough like a bubble to the point of rupture and indicates the gluten strength and extensibility of dough. Values reported include:
- P (“overpressure” or resistance), measured in millimeters to the maximum height of the curve, reflects the maximum pressure while blowing the bubble of dough and indicates dough resistance to extension.
- L (length), the length of the curve measured in millimeters, reflects the size of the bubble and indicates dough extensibility.
- W (the area under the curve) reflects the amount of energy needed to inflate the dough to the point of rupture and indicates dough strength.
The alveograph is well suited for measuring the dough characteristics of weaker gluten wheat and, with adaptive hydration and mix time, of stronger wheats including durum. Requirements differ depending on intended flour use. A low P value (indicating weak gluten) and long L value (high extensibility) are preferred for cakes and confectionery products; P/L close to 1 and high W values (strong gluten) are preferred for pan breads; and low P and long L values are favored for durum for pasta semolina.
The harvest and cargo samples for each class are evaluated using the following methods. Flour or semolina produced as described in “Laboratory Milling Extraction” is analyzed to provide flour, semolina and end-use product data.
Wheat and Grade Data
GRADE: Official U.S. Standards for Grain.
DOCKAGE: Official USDA procedure using the Carter Dockage Tester.
MOISTURE: HRW, HRS, SW, HW – Official USDA NIR method; Durum – AACC 44-11.01 (Motomco Moisture Meter) and AACC 44-15.02 (air oven method); SRW – AACC 44-15.02.
TEST WEIGHT: AACC 55-10.01; test weight is converted to hectoliter weight: for durum – kg/hl = lb/bu x 1.292 + 0.630, for other classes – kg/hl = lb/bu x 1.292 + 1.419.
PROTEIN: HRW, HRS, SW, HW – AACC 39-25.01 (NIR method); all other classes – AACC 46-30.01 (Dumas combustion nitrogen analysis or CNA method).
SINGLE KERNEL CHARACTERIZATION: AACC 54-31.01 using Perten SKCS 4100 for wheat kernel hardness.
SEDIMENTATION: HRS, HRW (Midwestern), SRW, SW, HW – AACC 56-61.02; Durum – AACC 56-70.01; HRW California (CA) – AACC 56-63.01.
1000 KERNEL WEIGHT: HRS, Durum, SRW – based on a 10 gram (g) clean wheat sample counted by an electronic counter; SW, HW – based on the average weight of three 100-kernel samples expressed on a 14% moisture basis (mb); HRW – average of SKCS kernel weight times 1000.
ASH: AACC 08-01.01 expressed on a 14% mb.
FALLING NUMBER: AACC 56-81.03; average value is a simple mean of sample results.
DON: All analysis is on ground wheat. HRS, Durum – gas chromatograph with electron capture detector as described in the Journal of the Association of Official Analytical Chemists 79,472 (1996). SRW, HRW (CA) – Neogen ELISA; HRW (Midwestern) – Charm ROSA DonQ2 Quantitative Test.
VITREOUS KERNELS: HRS and Durum – percentage by vitreous kernels weight handpicked from a 15 g clean wheat sample.
KERNEL SIZE DISTRIBUTION: HRS, Durum (Northern) – Cereal Foods World (Cereal Science Today) 5:(3), 71 (1960). HRW (Midwestern), SW, HW, SRW – Wheat is sifted with a RoTap sifter using Tyler No. 7 (2.82 mm) and No. 9 (2.00 mm) screens. HRW (CA), Durum (Pacific Southwest) – uses U.S. Standard Sieves No. 7 (2.80 mm) and No. 10 (2.00 mm). Kernels remaining on the No. 7 screen are “Large,” passing through the No. 7 screen but not the No. 9 or No. 10 (HRW (CA), Pacific Southwest Durum) are “Medium,” and passing through the No. 9 or No. 10 screen are “Small.”
LABORATORY MILLING EXTRACTION: Samples are cleaned and tempered according to AACC 26-10.02. All samples other than HRW (CA) are milled with standardized mill settings on a Buhler laboratory mill using these methods: SW – AACC 26-31.01; HRW (Midwestern), SRW, HRS and HW – AACC 26-21.02. HRW (CA) is milled on a Brabender® Quadrumat Senior mill using the Brabender® procedure. All extraction rates are calculated against total products on an “as is” moisture basis.
ASH: AACC 08-01.01, reported on 14% mb.
COLOR: HRW (Midwestern) – Minolta method using Minolta Chroma Meter CR-110 with Granular-Materials Attachment; HRW (CA) – CR-210; HRS, SW, SRW, HW – CR-410 with Granular-Materials Attachment CR-A50. CIE 1976 L*a*b* color system: L* indicates white-black, a* – red-green and b* – yellow-blue.
PROTEIN: HRW, HRS – AACC 39-10.01 (NIR method); all other classes – AACC 46-30.01 (Dumas CNA method).
WET GLUTEN AND GLUTEN INDEX: HRW, HRS, SRW, HW – AACC 38-12.02; SW – AACC 38-12.02 (water reduced from 4.8 to 4.2 ml).
FALLING NUMBER: AACC 56-81.03; average value is a simple mean of sample results.
FARINOGRAPH: AACC 54-21.02 (Constant Flour Method) with 50 g bowl. Absorption is reported on 14% mb.
ALVEOGRAPH: AACC 54-30.02. SW, HW – Alveolab.
AMYLOGRAPH: AACC 22-10.01 modified to use 65 g flour (14% mb) and 450 ml distilled water with paddle (HRS) or pins (other classes).
EXTENSOGRAPH: AACC 54-10.01, modified 45-min and 135-min rest for HRS, HRW, HW; 45-min rest for SW and SRW.
STARCH DAMAGE: SRW – AACC 76-30.02; all other classes – AACC 76-33.01 (SDmatic method).
SOLVENT RETENTION CAPACITY (SRC): AACC 56-11.02.
LABORATORY MILLING EXTRACTION: Samples are milled using a modified Buhler lab mill with identical settings and equipped with Miag laboratory purifiers, as described by Vasiljevic and Banasik 1980: Quality Testing Methods for Durum Wheat and Its Products, pp. 64-72, Dept. of Cereal Chemistry and Technology, NDSU, Fargo, ND. Roll gaps are modified to (in mm): B1-0.762; B2-0.305; B3-0.254; R1-0.102; B4-0.076; B5-0.038. Extraction rates are calculated against total products on an “as is” moisture basis. Procedure is derived from AACC 26-41.02 based on research showing improved correlation between laboratory and commercially milled semolina quality.
ASH: AACC 08-01.01 on 14.0% mb.
COLOR: Minolta Method using Minolta Chroma Meter CR-410 (Northern) or CR-210 (Pacific Southwest) with Granular-Materials Attachment.
PROTEIN: AACC 46-30.01 (Dumas CNA method).
WET GLUTEN AND GLUTEN INDEX: AACC 38-12.02 (Glutomatic procedure).
SPECKS: Sample is pressed under a 3-inch x 4-inch glass plate and the specks within a one-inch square marked on the plate are counted. Average of three determinations is expressed as specks per 10 square centimeters.
MIXOGRAPH: 10 g of semolina are mixed in a 10 g (Northern) or 35 g (Pacific Southwest) bowl with 5.8 ml of distilled water to give maximum dough consistency. A classification incorporating peak height and general curve characteristics is assigned based on comparison with eight reference mixograms; the higher the classification number, the stronger the curve type.
End-Use Product Data
MIDWESTERN HRW: AACC 10-10.03 (pup loaf method). 100 g flour at 14% mb with optimized water absorption is mixed to optimum development with other ingredients (6% sugar, 3% shortening, 1.5% salt, 1.0% instant dry yeast, 50 ppm ascorbic acid and 0.25% malted barley flour) in a 100g pin mixer with head speed of 100 to 125 rpm. The dough is fermented for 60 min with two punches, then molded, panned and proofed for 60 min before baking at 425 F for 18 min. Loaf volume is measured immediately after baking by rapeseed displacement. Crumb grain and texture are evaluated on a 0 to 6 scale, which for this booklet is converted to a 1 to 10 scale.
CA HRW: AACC 10-10.03 producing two loaves per batch using 6% sugar, 3% shortening, 1.5% salt, 1.5% active dry yeast, 50 ppm ascorbic acid, 0.10% malted barley flour in a 200 g Swanson pin mixer with head speed of 100 to 120 rpm and 120-min fermentation. Loaf volume is measured 1 hour after baking. Grain and texture are scored on a scale of 1 to 10 with higher numbers indicating preferred quality.
SRW: AACC 10-10.03 producing two loaves per batch using dry yeast and ascorbic acid. After mixing, the dough is divided into two equal portions, fermented for 160 min, molded and panned in “pup loaf” pans before proofing and baking. Loaf volume is measured immediately after baking by rapeseed displacement. SRW Cookie Spread Ratio – AACC 10-50.05.
HRS: AACC 10-09.01 (long fermentation method) modified: 15 SKB units fungal amylase/100 g flour; 1% instant dry yeast; 10 ppm ammonium phosphate; 2% added shortening. Dough is mechanically punched, molded and baked in “Shogren-type” pans. Scoring is based on a 1 to 10 scale with higher numbers indicating preferred quality attributes.
SW: Cookie diameter – AACC 10-52.02. Sponge cake volume* and score –- Japanese standard method described by Nagao in Cereal Chemistry 53:977-988, 1976. Sponge cake control flour is western white. SW High Protein – AACC 10-10.03 with 180-min fermentation for bread.*
DURUM: Pasta is made using the laboratory procedure described by Walsh, Ebeling and Dick, Cereal Foods World: 16: (11) 385 (1971). Water (Pacific Southwest – adjusted to optimum hydration based on P-value from Alveograph test; Northern – 32%) is added to semolina and mixed in a Hobart mixing bowl for 5 min. Semolina-water mixture is extruded using a DeMaco laboratory pasta extruder. Northern – Spaghetti is dried using modified Buhler high-temperature drying cycle as described by Debbouz, Pitz, Moore and D’Appolonia, Cereal Chemistry: 72 (1):128-131. Pacific Southwest – Spaghetti is dried using modified Buhler low-temperature drying cycle as described by P. Yue, P. Rayas-Duarte, and E. Elias, Cereal Chemistry 76(4):541–547. Color scores are determined by the procedure described by Walsh, Macaroni Journal 52: (4) 20 (1970), using a Minolta Color Difference Meter (Northern CR-410, Pacific Southwest CR-210). Higher values (scale 1 to 12) are preferred. Cooked weight, cooking loss and firmness are determined by AACC 16-50.01.
HW BAKING: AACC 10-10.03 with 180-min fermentation.*
HW NOODLE: Two noodle types are prepared from each HW flour: Chinese raw noodles and Chinese wet noodles. Raw noodle formula: flour 100%, salt 1.2% and distilled water 28%; wet noodle formula: flour 100%, salt 2%, K2CO3 0.45%, Na2CO3 0.45% and distilled water 32%. Noodle sheet color is measured twice on each side of a dough sheet that is resting atop a two other dough sheets to ensure color consistency. This is done for two dough sheets (eight readings total) using a Minolta CR-410 Chroma Meter; the mean value is reported.
For wet noodles, noodle sheet color is measured on both uncooked and parboiled (for 1.5 min) sheets. Cooking yield is percent of weight gain after cooking for 5 min for raw noodles and 1.5 min for wet noodles, rinsing in 26o-27o C water and draining. Sensory noodle color stability score is a total score of noodle color rated at 2 and 24 hours against a control sample (an assigned score of 7) and is reported based on a 1 to 10 scale; higher scores indicate better color stability. Noodle texture is determined on five strands of cooked noodles with a strand cross-cut dimension of 2.5 x 1.2 mm for raw noodles, W x T; 1.7 x 1.6 mm for wet noodles, W x T using a Stable Micro Systems TA.XT2 Texture Analyzer. Firmness indicates noodle bite; springiness indicates the degree of recovery after first bite; cohesiveness is a measure of noodle structure disruption during first bite; and chewiness is a product of firmness, cohesiveness and springiness (firmness x cohesiveness x springiness) and thus is a single parameter that incorporates the three textural parameters. Higher textural parameter values are generally more desirable for Chinese-style noodles.
CHINESE STEAMED BREAD: Two types of steamed breads are prepared: Chinese southern-type steamed breads from each of the SW and club wheat flours and Asian-type steamed breads from each of the HW flours. Chinese southern-type formula: flour 100%, sugar 15%, shortening 4%, baking powder 1.2%, instant yeast 0.8%, nonfat dry milk powder 3% and water 39 to 43%; Asian-type formula: flour 100%, instant yeast 1.5%, sugar 12%, shortening 2% and water 42.5 to 45%. Yeast is dissolved in water before use. All steamed breads are prepared using no-time dough methods (Wheat Marketing Center protocols). The total product score comprises volume*, external characteristics, internal characteristics, eating quality and flavor. Each property is rated compared with a control sample. The control flour is scored 70.
*Finished Product Volume for SW bread, sponge cake and steamed bread and HW bread and steamed bread: Laser light using a Tex Vol Instrument (BVM-L370).