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Endosperm Separation Index (ESI)
ESI was calculated as described by Yamazaki and Andrews (1982). ESI is the estimated endosperm adhering to bran and bran pieces after the third through fifth break passes and first reduction pass, expressed as a percentage based on the weight of milled grain divided into the flour recovered in the break rolls after the second break stream and the reduction rolls after the first break. Lower ESI values indicate better bran separation from endosperm and better milling quality than higher ESI values.
The quantities of final bran plus four other bran-rich fractions obtained at an intermediate stage of milling are recorded and essentially represent all of the bran. The bran (14.5%) and the germ (2.5%) are subtracted to yield endosperm remaining attached to the bran. The lower that value is, the better the separation was between endosperm and bran. Thus, a lower ESI value indicates better wheat for milling since less energy is required to produce straight-grade flour.
Friability
Gaines et al., 20001, estimated the ease with which mill stock is reduced to flour. Friability is calculated by dividing the weight of flour recovered during milling by the summed weight of mill stock passed through all roll stands, break and reduction, after the first break. The earlier in the break and reduction process that flour is recovered, the lower the weight of mill stock that passes to the later break and reduction rolls. Higher values of friability indicate better milling efficiency and reduced energy requirements to recover flour.
Friability is the tendency of the wheat endosperm conglomerates to reduce to flour as a result of corrugated and smooth roll action. The cumulative quantity of stock entering the rolls (usually 20 streams) and the percent of flour extracted from the stock relate to the total energy consumed by the milling process. A higher percentage of friability means that less energy is required per unit of flour extraction.
Friabilities above 30.5% are rare and only exceptionally good milling wheats fall into this category. Those cultivars displaying friabilities below 27% usually reflect very poor reduction of middling stock on the smooth rolls.
Poor milling-quality cultivars produce middling stocks which do not release flour well after being crushed on the smooth rolls, resulting in higher quantities of carry-over to subsequent reduction rolls. Cultivars that have reduced milling properties due to "weathering" do not reduce well on the smooth rolls and the endosperm and bran do not separate well on the corrugated rolls.
Milling a cultivar with a friability of 25% compared to one of 30% would produce about a 15% increase in the amount of stock entering the corrugated and smooth rolls of the SWQL Allis-Chalmers mill. When milling 60,000 # (1000 bu) of wheat per hour, the quantity passing thru the SWQL mill (not including 1st break) would be 179,000 # of stock for the cultivar with lower friability compared to 156,000 # for the cultivar with higher friability. The cultivar with friability of 25% would also yield about 3.5% less flour.
Flour Yield
Flour yield "as is" is calculated as the bran weight (over 40 weight) subtracted from the grain weight, divided by grain weight and times 100 to equal "as is" flour yield. Flour yield is calculated to a 15% grain moisture basis as follows: flour moisture is regressed to predict the grain moisture of the wheat when it went into the Quad Mill using the formula
Initial grain moisture = 1.3429 * (flour moisture) - 4.
The flour yields are corrected back to 15% grain moisture after estimating the initial grain moisture using the formula
Flour Yield(15%) = Flour Yield(as is) - 1.61% *
(15% - Actual flour moisture)
Softness Equivalent
Softness Equivalent "as is" is calculated from the fraction of mill product that is in the mids, with smaller amounts of mids correlating to smaller particle size, greater break flour yield, and greater softness equivalent. The mids weight (over 94) is subtracted from the unadjusted flour yield to calculate the quantity of fine flour that passed through the 94 mesh, which is divided by the unadjusted flour yield and multiplied by 100%. Softness Equivalent at 15% grain moisture is calculated using the estimated grain moisture prior to milling (see milling formulas). The softness equivalents are adjusted to 15% grain moisture with the formula
Softness Equivalent(15%) = Softness Equivalent(as is) - 1.08%
* (15% - Actual flour moisture)
Flour Yield Adjustment
Flour yield adjustment2 based on flour particle size 52% is subtracted from the actual softness equivalent. That difference is multiplied times 0.17% which is the change in flour yield per percentage point change in softness equivalent. Therefore3,
Adjusted Flour Yield = Flour Yield(15%)
+ (Softness Equivalent(15%) - 52%)
Mill Score
Mill score represents a standard adjustment based on flour yield by comparing the test cultivar to a check. The check cultivar produces a score that can be used as a handicap against its traditional expected yield, and the test cultivar mill score is adjusted to the same degree as the check. This method relates test cultivars providing a score that is independent of the environmental influences. The mill score standard deviation will be about 1.43 when evaluating cultivars and test lines that have been grown and harvested together.
- Gaines, C.S., P.L. Finney, and L.C. Andrews. 2000. Developing agreement between very short flow and longer flow test wheat mills. Cereal Sci. 77:187-192.
- On the small Quad Mill, coarser type soft wheats will appear to mill better than they should and conversely, softer type soft wheats will have suppressed "as is" flour yields.
- Micro milling adjustments were developed by Lonnie Andrews with Patrick Finney and Charles Gaines. Additional details are included in the Standard Operating Procedures for the Soft Wheat Quality Laboratory.
