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LABORATORY ASSESSMENT OF THE MILLING PERFORMANCE INDEX (MPI) OF STANDARD WHEAT
Laboratory milling is a very important part of wheat quality control procedures. There is a need to laboratory mill wheat, in a repeatable and reproducible manner in order to obtain flour for further analysis. However, the only parameters
operators routinely consider are flour extraction and ash content. Although these parameters are valuable, they are quite limiting in the information that can be obtained regarding wheat behavior during milling.
Experience shows that flour extraction and wheat behavior during milling are two different things. It makes sense for millers to select wheats with the highest extraction potential but also wheats performing consistently in their production
MATERIALS AND METHODS
150 wheats from 14 countries have been analyzed using the CHOPIN Experimental mill (LabMill-Standard setting picture 1). Wheat tempering was performed at 16% moisture, 24h resting time according to ISO 27971.
The milling diagram for the LabMill (Scheme 1) consists of 2 breaks (equipped with corrugated rolls), 1 sizing (smooth rolls) and 3 reductions (Smooth rolls). After each pass, products are separated through a centrifugal sieving system. A total of 20 different fractions consisting of flours, middlings, brans and shorts give a complete break down
of how wheat are performing in a standard milling process.
In order to simplify the use of this very detailed information, we created a Milling Performance Index consisting of 3 indices ranging from 1 to 7.
• Resistance Index: calculates the ratio of fine products/coarse products during 1st break. If the ratio is low, meaning more coarse products, wheat will be considered "resistant" and will be attributed a "7".
• Dissociation Index: calculates the ratio of fine middlings/coarse middlings during 1st and 2nd breaks. If the ratio is low, meaning more coarse middlings production, wheat will be considered "hard to dissociate" and will be attributed a "7".
• Reduction Index: Calculates the amount of reduction flour obtained from the fine middlings quantity sent to reduction. The lower the amount, the more difficult it will be to produce flour and wheat will be attributed a "7".
Results were analyzed and projected to a "virtual" LabMill diagram (Scheme 2) with a 10t/hour wheat input at 1st break. Table 1 shows the results obtained with 5 samples having the same extraction rate but different MPI and another set of 5 samples having same MPI but different extraction rates.
Results clearly show that grouping samples by their MPI allows millers to have much better control of the wheat behavior during the milling process and thus to get the most benefit of it. This makes sense as it is possible to obtain the same final extraction with wheat having quite different behavior, for example one giving less flour during break
and more during reduction.
The proposal of the new Milling Performance Index brings a new perspective to experimental milling through a description of wheat behavior during milling. Data shows that, thanks to the complete information obtained from the different streams, the LabMill has a potential to establish a link between the laboratory and the production plant, selecting or blending wheats not only based on extraction rate but rather on their real grinding behavior during milling.