Enriching Flour, Enriching Lives: The Flour Fortification Initiative

22.3. Carriers and Physical Properties
Since micronutrients are added in minute quantities (ppm), they are difficult to feed accurately and uniformly through a feeder. This becomes even more challenging when the output of a flour production facility is very small. Therefore it is common practice to increase the bulk quantity of the premix containing the intended micronutrients by adding inert and free flowing material to help accomplish the uniform rate of addition.

In most premixes starch makes up the bulk of the material and is considered the carrier of choice. It is important for the premix colour to contrast as little as possible with the colour of the flour. Even though the addition rate may be only 125 to 150 grams per ton (1,000 kg) of flour its colour may still affect the appearance of the flour. Most premixes are either yellow or white. Particle size is also considered to be very important. In order to mix well with flour the particle size of the premix should be similar to that of the flour. At the same time, to ensure good free-flowing characteristics the particle size of the premix should not be too fine. Wide differences in particle size lead to stratification. Irrespective of their origin, most flours have particles finer than 150 μm. Therefore, premix particle sizes are generally required to be 99% finer than 100 mesh (equivalent to 150 μm).

Micronutrient premix is added well before the flour is rebolted (sifted) for either bulk delivery or packing. Although nylon sieves coarser than 150 μm are generally used for rebolting, 150 μm sieves are used in some cases. If the premix particle size is not in compliance with size specifications the premix may be sifted out.

22.4. Homogenizing
In North America most feeders are situated directly on a flour conveyor. As the flour is conveyed to the outlet it gets mixed with the various additives that continue to discharge from the feeders at desired preset quantities. The longer the flour conveyor, the more thorough will be the mixing. Feeders are therefore located on the conveyor in such a way that following the discharge of the powders the length of the conveyor is sufficient to allow a good mixing action. In those plants where feeders are located away from the flour conveyors and therefore a blowing line is used to transport the microingredients into the conveyor, the lines are connected in such a way that there is enough conveying length to permit good mixing.

The flour dropped down the spout is allowed to pass through a flour rebolter (small sifter) followed by an entoleter. These are used as a precaution to prevent any infestation from devel-oping and propagating. The entoleter has a rotor that consists of two discs separated by a number of concentric spindles. The rotor runs at a high speed of 2,900 rpm to 3,600 rpm within a conical casing. This facilitates the vigorous dispersion of the flour particles, allowing further mixing. So in those facilities where the flour conveyor used is small, this system helps to compensate somewhat. Flour from the entoleter then passes through a flour scale and enters a positive-pressure air line through an airlock. As the positive pressure blows the flour through the air line into the bin, the additives and the flour particles are homogenized further. The illustration in Fig. 105 shows the method described above.

Fig. 105: Continuous flour fortification in the mill

Batch mixing of flour ensures even more thorough and intimate mixing of flour with macro and micro ingredients and various other additives. This method is illustrated in Fig. 106.

Fig. 106: Flour fortification by batch blending

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