“The fundamental need for wheat blending is the information. Mill manager must know about the amount of wheat in stocks, current supply, silo capacities, market and customers in order to manage the wheat supply to his mill. Millers have uses simple mathematics in order to determine the ratios of what mixtures but modern computer software also give them the opportunity to optimize blending. They also allow millers to add more variables in the mixing equation to determine the most advantageous mixture.”
Prof. Dr. Farhan Alfin
Head of Food Engineering Department
Flour consumers like bakeries and biscuit manufacturers demand from millers to supply them high consistent quality flour or that is within the standards tolerating production lines and does not negatively affect the end product (Tanase, 2014).
Quality characteristics of the wheat depend upon wheat variety, ecologic conditions and cultural processes. Shifting between wheat varieties also changes milling quality and flour quality. (Türker and Elgün, 1997; Fowler, 2012). A wide range of wheat varieties causes different types of flours. Storage conditions and milling technology also plays role on the quality of the flour. When we talk about the ‘quality’ of a specific flour, we mean the suitability of this flour for a particular end use. Therefore, the miller should first select the wheat of desired quality in order to have a quality flour for the end use. (Türker and Elgün, 1997).
Millers buy wheat varieties with different characteristics to obtain various types of flour. But it may be hard to continuously find the wheat of desired quality for consistent flour production. As a result, it is difficult to maintain the quality of flour with a single wheat variety (Dündar and Zerenler, 2011). In order to maintain the high quality product at the end of the grinding process, millers must use different types of wheat with different quality when performing blending process one of the significant step of grinding process. Thanks to the blending, it becomes possible to maintain the same degree of quality that consumers demand (Türker and Elgün, 1997; Fowler, 2012; Tanase, 2014).
The blending process is carefully mixing two or more wheat varieties with a given ratio in order to obtain a mixture with desired characteristics. (Elgün and Ertugay, 2002; Ünver, 2005; Tanase, 2014).
The purpose of blending should be predefined to give miller the opportunity to take the best blending decision. Reasons for blending wheat and/or flour in the flour milling process can be categorized into three areas (Fowler, 2009; Fowler, 2012).
Consistency. As stated before, blending is an inevitable process for the miller to consistently have the same flour quality. In addition to this, delivering a uniform blend of wheat to the mill is vital to maximizing yield and mill efficiencies. Variations in the moisture, protein and density of wheat delivered to the mill can negatively affect mill balance and result in lower extraction rates and lower mill capacity.
Uniqueness. The ability to differentiate your product from the competition is important in marketing it to customers.
Cost control: The most common reason to blend is cost control. This involves blending wheat to meet the minimum quality requirements of the customers at the least possible wheat cost. This usually means blending the maximum amount of low-cost wheat into a higher-valued mix or blending a minimum amount of high-cost wheat into a low-cost mix. The aim is to minimize raw material costs while meeting quality needs and expectations of customers in a sustainable way. (Hass, 2011; Fowler, 2009).
WHEAT BLENDING IN MILL DIAGRAM
Wheat of various types are transferred to daily-silos after rough cleaning. In the mills with old technology, following the cleaning process, wheat are tempered only by one process and conditioned in wet silos. But in modern milling systems, there is a two tempering process. Therefore, blending can be applied at four points. The first point is at the exit of daily silos before cleaning and first tempering process. The second is after first tempering process at the exit of first conditioning silos. The third is before the milling system at the exit of the second conditioning silos. The fourth is mixing the flour during transferring it to packaging system at the exit of flour silos.
When separate cleaning and tempering processes are unnecessary since types of wheat are very close to each other in terms of characteristics, blending can be applied just after rough cleaning and before tempering (Elgün and Etuğay, 2002; Özkaya and Özkaya, 2005; Annon, 2016).
Since extremely hard or soft types of wheat requires different tempering conditions, it will be better to perform blending on separately cleaned and tempered wheat during feeding for grinding (Elgün and Etuğay, 2002; Özkaya and Özkaya, 2005; Ünver, 2005; Posner, 2009; Annon, 2016). This can only be done in factories with many conditioning silos (wet silos) (Ünver, 2005). If blending is performed before tempering on wheat types with different characteristics, desired quality standards are not met, and the ground wheat will end up with low quality flour. On the other hand, it is possible to maintain the quality when blending is made after tempering and during feeding for grinding. Even certain values show deviation, blending ratios can be changed swiftly in order to prevent possible decrease in quality (Annon, 2016).
It is crucial to perform the blending after tempering. Because, in order to organize the time for water penetration to the center of the grain, the amount of water should be determined according to the hardness of the wheat structure. But if two different types of wheat are tempered together, humidity will not be homogeneous. As a result, one type of wheat can be extremely soft while the other type can remain dry (Posner and Hibbs, 2005; Annon, 2016).
On the other hand, mills with many silos and flour mixing facilities can blend various types of flour after grinding, rather than blending different types of wheat. Blending various types of flour ground separately or obtaining a mixture of flour is the latest step to ensure flour quality before packaging in order to prevent deviation from customer needs. As a result, quality standards are met and maintained, regulatory compliance is ensured easily. The most important point is that, wheat blending is not linear, but flour blending is linear and ensures exact results (Ünver, 2005; Posner, 2009).
When applying calculated wheat ratios, technical aspects of blending process should be efficient. Even if you have the best quality of information about blending, facilities with poor technical equipment can not benefit from those information. Wheat flow from silo affects certainty of blending process. Grain size or density differences might affect the ratio and quality of wheat blending. In order to be able to perform a homogeneous blending process, silos should be designed to enable a smooth flow of mass (Posner and Hibbs, 2005). All wheat silos in a mill should be equipped with multiple exits for regular flow or first in first out flow. The wheat flown through silos goes to mixing conveyor after passing through the system. The length of the mixing conveyor is equal to total length of all silos containing the wheat to be mixed and should enable free flow for wheat. Mixing conveyors should be screw-type in order to obtain better results (Sugden, 1996).
Wheat Blending Systems
The amount of flowing wheat can be determined in terms of weight or volume. Volumetric scales and automatic weighing machines or gravimetric dosing scales are used for this (Özkaya and Özkaya, 2005; Tanase, 2014). Accuracy of scaling the wheat amount depends on working principle of the scale, amount and ratio of foreign materials within wheat and uniformity of the flow. (Posner, 2009).
Volumetric scales are cheaper and simpler than weighing machines. Furthermore, they require a minimum area and space. But as it is difficult to convert the volume of wheat into a weight unit so stock calculations may not be accurate (Sugden, 1996).
Weight based mixture systems have different levels of precision and high-accuracy scales are more expensive. Small and high-precision scales are the most expensive ones. Another popular type is the gravimetric feeder which is more expensive than volumetric tools but cheaper than regular weighing machines. It also requires less space (Sugden, 1996).
Although blending can be done using volumetric scales for different types of wheat with the same or similar intensity, synchronized automatic gravimetric machines are preferred to get a more prices measurement (Özkaya and Özkaya, 2005).
Automatic Weighing Scales
This is a tool to automatically weigh flowing wheat in batches and count and save the number of batches (Özkaya and Özkaya).
Volumetric Dosing (Volumetric Scales)
Volumetric dosing is also a reliable method despite giving less precis results than weighing tools. Volumetric dosing machines should be used at the exit of silos in order to perform this method. There are two main types of volumetric dosing machines.
The first type has cells of constant volumes like a standard airlock. But its speed can be changed by using inverters or gear cases. Furthermore, volumetric capacity or rotations should be known.
The second type usually has dosing cylinders split to 5 or 6 parts and turning slowly and with a constant speed and has special volumetric capacity and revolutions. These types of machines are called Volumetric Dosing Machine. This type can be fed with different ratios from 100% to 10%. First type is more expensive, but it allows feed ratio from 100% to 2%.
They can be used with a single material or with a maximum of 4 or 5 materials. (Figure 1). Capacities of those Dosing Machines may change between hundreds kg/h to 15-20 tons/h. A sensors of minimum level of should be available at outages of silos for safety reasons (Sugden, 1996; Tanase, 2014).
Gravimetric dosing machines are operated automatically in a continuous way and can be controlled electronically. It is more prices than volumetric dosing systems because it allows continuous flowing independently of hectoliter weight or changes in flowing characteristics of wheat. In addition to this, amount of the wheat is completely or partially recorded, therefore stock calculations will give better results.
It is preferred in modern, fully automated and digitalized mills because it enables full automation via computers. A system with multi-machines connected to a centralized computer system allows preparation of mixtures with the help of programmed instructions and a database. (Tanase, 2014). The most popular Gravimetric Dosing Machines work according to principles of “Impact plate” or “Weight loss” principles.
Impact Plate Dosing Machine
Some multi-purpose gravimetric systems that are among most precise scales, make measurements based on impact plate technique which creates a central force. Tools based upon impact plate technique (Figure 2) usually has an electrical or air pressure mechanism at intake part in order to regulate wheat flow (Figure 2, part 2). At this figure, high corrosivity resistant curved impact plate (part 3) is mounted onto a force converter which is generally is a load cell (part 4) in order to measure the force which is proportional to flowing wheat mass. Analog signals are converted to digital signals via a special interface based on algorithms and processed by an integrated or remote electronic unit (part 5). A central PC station can be used to program and display various information in order to control the whole dosing process and to direct alerts and also another optional electronic unit for communication.
Weight Loss Dosing Machine
Tools that based on weight loss technique are more complicate than impact plate dosing machine and they can be used to dose mass flow as well as volumetric flow. Weight loss based systems consist of a vessel mounted to load cells and at outlet unit a feeder to regulate product flow rate. The system monitors the weight loss during pouring the wheat out of the vessel and product flow is continuously adjusted to ensure that dosing is going on as planned. When detected weight drops to a minimum value, control unit closes the feeding system. The vessel is filled again, and the cycle is repeated. System can also monitor weighing chamber or discharge velocity as an optional feature. Furthermore, it can display other data about the product like hectoliter weight (Tasane, 2014).
Determining Blending Ratio:
The fundamental need for wheat blending is the information. Mill manager must know about the amount of wheat in stocks, current supply, silo capacities, market and customers in order to manage the wheat supply to his mill. Various options and opportunities are available for wheat blending. If the mill manager has good relationships with a what supplier, it may be possible for him to obtain customized wheat mixes that are prepared in shipping silos before delivery. (Fowler, 2009).
The blending is performed to adjust wheat values like moisture, sedimentation, enzymatic activity, ash etc. to the desired level. Characteristic of the wheat should be known before the blending process is performed. So, after laboratory work, different types of wheat with different quality are blended at ideal ratios (Elgün and Ertuğay, 2002; Dündar and Zerenler, 2011; Ünver, 2005; Özkaya and Özkaya, 2005; Posner and Hibbs, 2005; Tasane, 2014).
In order to determine the quality of a wheat mixture, the following formula is used:
K : the value of average quality characteristics of the mixture to be prepared for grinding
Mi : the amount of wheat of “i” variety.
Ki : the value of measured average quality of Mi
In order to calculate ratios of two different types of wheat according to a single criterion, the most practical method will be PEARSON SQUARE. According to this method, if we need a blend with a protein content of 12% from two wheat varieties of A and B with protein content of 9% and 14% respectively;
We take 2 units of variety (A) and 3 unites from variety (B) and mix them to obtain a blend with 12%. This mixture gives a flour type with 11% after milling processes. (Elgün and Ertugay, 2002).
Millers have uses simple mathematics in order to determine the ratios of what mixtures but modern computer software also give them the opportunity to optimize blending. They also allow millers to add more variables in the mixing equation to determine the most advantageous mixture.
Millers also take various factors like wheat characteristics, availability, convenience and price into consideration when blending (Türker and Elgün, 1997). One of the most important factors is quality characteristics of the flour to be compatible with the demand. Linear programming has been used to calculate the most cost effective ratios meeting requirements at an acceptable level (Hayta and Çakmaklı, 2001; Posner and Hibbs, 2005). You can find an Excel sheet showing a brief linear programming method to calculate the optimum wheat mixture that is the most effective in terms of cost. First of all; wheat characteristics, flour values and costs are entered as shown in Figure 3
In B11 cell “=B3*H3+B4*H4+B5*H5+B6*H6”,
In C11 cell “=C3*H3+C4*H4+C5*H5+C6*H6”
In D11 cell “=D3*H3+D4*H4+D5*H5+D6*H6”
In E11 cell “=E3*H3+E4*H4+E5*H5+E6*H6”
In G11 cell “=G3*H3+G4*H4+G5*H5+G6*H6”
In H8 cell “=SUM(H3:H7)”
Click on Data > Solver from the Excel menu. Enter the parameters and click on Solve as shown in Figure 4. Results will be calculated by Excel as shown in Figure 5.
As shown in Figure 5; ratios should be as following: 22% from variety 1.33% from variety 3 and 44% from variety 4. The lowest cost blend will cost 1.5 TL/kg. Characteristic of the blend will be as the following: 27.61 gluten, 85.00 gluten index, 35.56 sedimentation and 190 W Chopin. Adding other restrictions is also possible.
Note: The excel file can be asked from email@example.com