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Wheat Conditioning and Tempering

08 December 20208 min reading

Prof. Farhan Alfin

“Reducing tempering time was the aim of modern dampening equipment, which based on the increasing the rate of water penetration by reducing water surface tension by generating high frequency vibration. Reducing water surface tension enhance the efficiency of water dispersion over the grain mass and water penetration into the kernel. This equipment does not break the kernel because it does not include scouring process.”

Professional millers know that wheat cleaning and preparing stages are important as milling system to have balanced mill, which is responsible to have the highest flour extraction and best flour quality.

Conditioning is the critical part of wheat preparation system for milling. Conditioning process is adding water (or worm water if the wheat or weather is cold) to the wheat and followed by a rest period in tempering bins until the added water penetrates the kernel and reaches the optimum moisture distribution which helps to prepare the wheat for optimum milling. “Tempering” is a term refer to the rest period.

If the wheat is milled without conditioning the bran becomes brittle, and turns into small particles during milling by the roller mills, which contaminate the produced flour. Therefore, the produced flour ash content will be high. Milling energy will be high, the damaged starch of produced flour will be high, it will produce sticky dough, and its baking qualities would be low.

Whole wheat flour is sometime produced by milling wheat without conditioning.

BENEFITS OF CONDITIONING

The objectives in the conditioning process are: 1- To toughen the bran but not so much to remain in large particles during the milling process, avoid production of small bran particles and enable the endosperm to separated more efficiently from the bran. Shattered small pieces of bran contaminate the clean, white endosperm, produce flour with high ash content. Therefore, wheat conditioning process gives high flour extraction with lower ash content.

2- To toughen up the germ to separate it from the endosperm more easily. The germ is rich in fat. Germ contamination of flour shortens the shelf life of flour.

3- To gives the endosperm optimal mellowness that minimizes energy consumption during grinding. In other world to achieve optimal milling conditions. If the wheat is wetter or drier in relation to its optimum milling conditions, the system will be out of optimum balance, which results in reduction of flour extraction and nonuniform flour characteristics.

4- To maintain enough endosperm hardness to produce desired amount of starch damage, and optimal particle size distribution.

5- To achieve optimal sieving. Appropriate amounts of the kernel fractions flow to all grinding stages gives optimally balanced milling system.

6- To secure the correct percentage of moisture in the finished product. Dry flour also will decrease baking qualities. The gluten matrix will take much longer to develop and not be fully hydrated. The result is dry, crumbly, tough bread dough.

MOISTURE CONTENT

Generally, the optimum wheat moisture content before first milling machine optimum milling moisture is between 15 and 17%. Moisture distribution among the kernel parts have to be optimum too. For example, if the bran has about 14% moisture and the endosperm have 17% may result dark flour color. On the other hand, if the endosperm moisture at 14.5% and the bran at 18.5% would affect flour yield and the balance of the mill.

The optimum milling moisture depend on the following factors: • Type of wheat (soft, hard, semi hard), recommended milling moisture for hard wheat 16.0-17.0%, semi-hard wheat 15.5-16.0%, semi soft wheat 15.0-15.5% soft wheat 14.5-15.0%. • The loss of moisture during milling process because of water evaporation. Moisture loss must be monitored by the miller and compensated for by controlling the amount of added water during conditioning. The mill environment temperature and relative humidity, heat generated during milling are among of the factors which influence the amount of moisture loss. • The desired flour yields. As desired flour extraction increase the optimum moisture content decrease. • The desired moisture content of the final products. The rate of conditioning water can be calculated by following equation:

where: “W” is equal to the rate of water required (l/h); “C” is equal to the capacity of grain (kg/h); “Mf” is equal to the target moisture content; and “Mi” is the initial moisture content.

CONDITIONING EQUIPMENT

One of the main goals of wheat conditioning systems before tempering is to distribute the added water uniformly in all the kernels of the wheat mix. Generally, tempering mixers can be categorized according to mixing speed and its chamber incline. Chamber of tempering mixer can be horizontal and inclined. In each of tempering mixer position, the mixing speed could be low-speed and high -speed. Low speed tempering mixer are actually a screw conveyor but with angled paddles. Capacity of mixer and retention time can be adjusted by the angle of paddles on the shaft.

High-speed mixers, commonly referred to as intensive dampeners. Intensive dampener and inclined intensive dampener are the common tempering systems used nowadays. Intensive dampeners disperse the water in the grain mass by an intensive mixer in which the wheat is tumbled with the added water very rapidly. Intensive dampener secure uniform distribution of the added water over all parts of each kernel. As a result of using intensive dampener the addition of up to 7% can be achieved in one step with very uniform water dispersion which decrease the necessary tempering bins capacity than multistep methods. Intensive dampener process increases the water penetration rate into kernel by scouring the wheat bran and reducing water surface tension.

Since intensive damping system reduces tempering time and makes no need for second conditioning process it reduces bacterial growth and considered as highly sanitary.

MODERN DAMPENING EQUIPMENT

Reducing tempering time was the aim of modern dampening equipment, which based on the increasing the rate of water penetration by reducing water surface tension by generating high frequency vibration. Reducing water surface tension enhance the efficiency of water dispersion over the grain mass and water penetration into the kernel. This equipment does not break the kernel because it does not include scouring process.

Debranning “stripping” or “peeling” of wheat kernel can be used to enhance the water penetration rate which reduces the tempering time. These techniques remove or damage the wheat kernel bran layers using high abrasion and friction machines just before milling. Higher flour extraction and lower ash content are among of the advantages of these methods.

TEMPERING BINS

As described earlier, after water adding to wheat, it is left to rest in tempering bins to enable the water to penetrate into wheat kernel. Steel or concrete bins can be used for tempering. The tempering bins should be designed with multiple outlets have openings with a minimum diameter of about 155 mm to secure a mass flow of tempered wheat where the earlier tempered wheat leaves the bin first that can be described as FIFO “first in, first out”.

Tempering bins capacity depends on resting time and milling system capacity. Tempering bins capacity can be calculated by following equation:

MULTIPLE STAGE TEMPERING

Multiple stage tempering should be used if the mill processes different type of wheat especially if the wheat types are significantly different in hardness or size. To have the wheat and blended after first or second conditioning process. In these cases, the soft and hard wheat or big and small kernels wheat have to tempered for different periods so that should be conditioned separately and then blended before milling.

Produced flour color improving and reducing its ash content can be among of advantages of multiple stage tempering. In the second conditioning stage the wheat can be scoured and aspirated to remove partially the kernel barn.

Tempering Temperature

Tempering temperature affects water penetration rate into wheat kernel. Optimum temperature of wheat is in the range 23-27 °C. To achieve optimum conditioning in cold weather the used water temperature should not be below 25 °C. During the tempering period there is a natural rise of 4-6 °C in wheat temperature.

Tempering Time

The tempering time is related by the rate of water penetrating into kernel which depends on the damping method, the initial moisture content, kernel hardness, and kernel temperature. Damping with low-speed mixer can take up to 72 hours, while 7 to 12 hours using the intensive dampener. Generally, hard wheat types require long tempering time to achieve optimum water dispersion all over the kernel. Although, high moisture wheat requires lower amount of water than the dry one, the rate of water penetration is faster. In other words, lower initial moisture content, tempering time should be longer.

About Prof. Farhan Alfin, Prof. Dr. Farhan Alfin is working now as a production supervisor at Darıca Flour Mill (Trabzon – Turkey). He obtained his Ph.D. from Ege University in Izmir, Turkey, from the Department of Food Engineering in 2000. He worked at Avrasya University (Trabzon – Turkey) from 2015 to 2019 and held the position of Head of The Food Engineering Department. He worked at Al-Baath University in Homs City, Syria at the Food Engineering Department from 2000 to 2015, and he held the position of Head of Department from 2006 to 2010. During that period, he offered his consultancy and education services to several flour mills in Syria. On another level, he worked as the executive manager of Alakhras Mill in Rural Homs from 2009 to 2015. He is also the author of the “Cereal Milling Technology” book written in the Arabic language. Email: alfafin65@gmail.com
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