Influence of Rolls on Damaged Starch during Milling and Roll Adjustments
09 September 20144 min reading
“Damaged starch content changes with different pressures and roll gaps. While damaged starch content increases in narrow roll gaps; this amount decreases with the wide roll gaps. Thus, it is an essential issue to keep roll gaps and pressures under control. Improper roll gaps and pressures both affect the physical structure and functionality of the product adversely and thus brings economic problems together.”
Breaking and reducing rolls used on industrial milling, comprises deformation of wheat properly and becoming flour. During this process, embryo must be separated from bran without damaging other contents and endosperm must be ground with proper particle size. Precision of this action is highly important to obtain the flour with good physical, chemical and rheological conditions according the end use purpose. 2 types of rolls are used during the flour production process as breaking and reduction. Geared breaking rolls open the wheat and separate embryo and endosperm. Smoothed reduction rolls grind the endosperm gradually and take it to the intended particle size.
During all of this operation, starch structure which composes the 70% of wheat becomes physically damaged and “damaged starch” particles occur. This damage is a desired structure with optimum level. Standard starch particle absorbs 40% of its weight but damaged starch absorbs twice of this amount. Anyhow damaged starch seems really good for production, if the optimum level increases more than intended, it causes functional and physical problems on end product. Therefore damaged starch content must be under control all the time.
The main factor constituting the amount of the damaged starch that is already in the biological structure of wheat is the milling roll gaps. When this gap decreases, compression ratio and damaged starch content increases. An example study graph is given below:
As it is seen, damaged starch content changes with different pressures and roll gaps. While damaged starch content increases in narrow roll gaps; this amount decreases with the wide roll gaps. Thus, it is an essential issue to keep roll gaps and pressures under control. Improper roll gaps and pressures both affect the physical structure and functionality of the product adversely and thus brings economic problems together.
We can specify the damages that can be seen when the roll gaps are not proper as (when the roll gaps are operated below the optimum level (high pressure) and when they give much damage):
• Increase in the need of energy (electricity)
• Paying higher prices for raw material because of that the selection the correct wheat type cannot be realized
• Increase in the manpower cost
• Lower roll robust life (increase in depreciation)
• Product rejecting and complaints from customers because of improper product
Practical studies free from the theory on the subject was performed and it was seen that 26.000 kW energy saving was provided with controlling damaged starch content and roll gaps in a flour mill being operated for 300 days in France in 2012. Economical profit is for this saving is 3.250 € when the energy prices in France are taken into consideration. In the opposite situation; in other words in a study in which low-damaged starch with pressure of the roll gaps lower than the required amount, yield decreased, end product quality was not at the desired level and economic losses occurred again . In this study, it was seen that flour was produced with 79% yield by assuming that the roll adjustments are not checked in a mill with 200 ton/day capacity and being operated with 80%. Daily 280 dollar-loss was seen. This amount caused approximately 4.000-dollar loss in 2 weeks.
As it is seen, roll adjustments are highly important and it is not enough to adjust it with the traditional methods. The most effective method is measuring the damaged starch content continuously and taking the roll gaps under control all the time. Measuring damaged starch is possible as colorimetric, enzymatic and amperometric. The most accurate, fastest and lowest consumption is amperometric method and it is used in Turkey and all around the world frequently widely for more than 10 years with the “SDmatic Damaged Starch” device found by Chopin Technologies SA.
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