Miller Magazine Issue 137 May 2021

64 COVER STORY MILLER / may 2021 cess itself is a collection of operations that involves sev- eral steps which includes; preparing for milling raw ma- terial by proper tempering, and efficient grinding. These are factors which can influence the mill extraction. • Dampening and tempering of wheat Tempering is the process of adding water to wheat before milling to toughen the bran and mellow the en- dosperm of the kernel and thus improve the efficiency of flour extraction. After the separation of all the impuri- ties and the adhering surface dirt, the cleaned wheat is then dampened using an automatic dampener(Turborliz- er) and thoroughly mixed in a special type of dampening worm or in a rapid dampener. Depending on the hardness, temperature of the wheat, initial moisture content, and condition of the out- er bran layers, the wheat is allowed to rest in so-called conditioning bins for varying durations of time, in order to allow the required time for the water to penetrate in- side the grain and get evenly distributed over the entire grain. This is called the Tempering time or conditioning time. Especially the epidermis and seed coat, distribution of the water onto the kernel surface, quantity of protein. The tempering time indicated in Table: However, as tempering moisture within the kernel in- creased, flour extraction rate decreased. Therefore, the tempering procedure should balance the level of flour extraction and the acceptable level of bran in flour. The preparation of wheat by repeatedly dampening and conditioning is aimed at bringing the wheat to an ideal condition suitable for milling. By ensuring the ideal distri- bution of water within the kernel, optimum milling results can be achieved. Most tempering studies have focused on tempering mechanism and milling yield but not flour quality. Few re- ports link tempering effects to flour qualities such as ash content, farinograph, and extensograph quality. Wheat with constant humidity will create conditions for stable milling, a loading at relatively constant flows of products, cleaner intermediate products, finished products with lower and constant ash content, products of a granula- tion corresponding to the final goal and not ultimately minimal specific power consumption. • Grinding system This is the section where the real milling of raw wheat to flour takes place. It consists of the Break system, Grad- ing or Sifting, Purification, Scratch system, and Reduction system; in which the number of passages is decided on the mill flow sheet based on the type of raw material e.g. (Wheat), to be milled and the finished product to be pro- duced. A wheat kernel is made up of three main parts: bran, germ, and endosperm. One of the main goals of the wheat miller is to separate the wheat kernel as efficient- ly and completely as possible into these three parts as shown in (fig 1). This separation determines the percent of the kernel that is converted to flour. A key consideration is not to remove too much of the bran layers with the endosperm. Removing bran with endosperm causes flour ash content to increase which decreases the baking quality of the flour. Equipment within the grinding section has different technological features. Relating to the equipment, we classify the factors influencing the extraction in two ma- jor groups, namely: a. Factors related to the technological features of the equipment b. Factors related to the plant concept, the mill flow diagram Each machine within the grinding section has certain technological features. They are not chosen at random but are a whole. An incorrect corrugation at B1 will imme- diately affect the plant performance. This is valid also for sifting, semolina purifiers, etc. Break System The aim of the break system is to break up the wheat kernel, separate the bran from the endosperm as effi- ciently as possible. To achieve this aim the following key- note needs to be put into consideration: • Proper wheat dampning and tempering • Gentle grinding of the break roll • Good condition of the roll flutes and proper roll dif- ferential • Use of bran finisher IMPROVING MILLING PERFORMANCE Type of Wheat Tempering time (h) Very hard wheat 36-48 Hard 24-36 Semi-hard 18-24 Semi-soft 12-18 Soft 6-12