What is Wheat Endosperm?
Wheat endosperm is the major storage tissue of a kernel of wheat. It is found between the bran and the germ. The endosperm is of great importance during wheat milling since it contributes the bulk of the material that is used in the manufacture of refined wheat flour.
The endosperm consists of the following:
- Starch
- Proteins
- Mineral
- Moisture
- Lipids and other components in small amounts
Generally, starch is the major component of endosperm. The proteins of wheat are also important since some of them are responsible for gluten formation when flour is mixed with water.
The physical structure of the endosperm also plays a role. Hard endosperm breaks differently during milling than soft endosperm. The way the flour particles break also differs. This is especially evident when a comparison is done of flour made from wheat with hard endosperm versus that made from wheat with soft endosperm. It is therefore important to select the appropriate wheat and understand the characteristics of the endosperm in order to improve the texture of flour.
Factors Affecting Flour Texture
There are many factors that influence flour texture. These factors include particle size and particle shape, starch condition, proteins, and moisture content, milling techniques and storage time.
Wheat endosperm provides the raw materials for these factors. If wheat is correctly milled, then the endosperm can provide flour particles of relatively the same size. Smaller particles promote uniformity, and larger particles promote hydration and dough development.
A good milling process is able to manufacture flour with consistent physical and functional properties.
For example, to make good cake flour, the protein and gluten would need to be developed to a lower level than that of bread flour; and the particle-size distribution and/or the shape of the flour particles would likely need to be different.
As such, there is not a single “best” wheat endosperm texture for all applications of flour.
The ideal endosperm would need to be defined for the production that the flour is designed for.
Selecting Wheat for Better Flour Texture
There are different types of wheat, and each has different endosperm characteristics. Hard wheat has a firmer endosperm, while the endosperm of soft wheat is softer. How wheat endosperm is structured effects how the wheat flour functions, and how the wheat flour can be milled.
There are other characteristics of the wheat that also determine the quality of the flour:
- The quantity of protein
- The moisture of the kernel
- The size of the kernel
- The weight of the kernel
- The potential for damaged starch
- The cleanness of the grain
- The variety of the wheat
- How the wheat was grown
- How the wheat was stored
The quality of the wheat and how well it meets the desired end use, gives the miller a solid base for the production of desired flour texture.
Wheat Kernel Structure and Its Role in Milling
A wheat kernel consists of three main components: bran, germ and endosperm.
The bran is the hard outer covering. It includes plenty of dietary fiber, minerals, and other substances.
The germ is the embryo of the wheat plant. It has oil, protein, vitamins, and other substances.
The endosperm is the largest part of the kernel. It is the source of the flour.
The goal of conventional flour milling is to open the kernel and slowly remove the bran and germ from the endosperm. This is not achieved by simply crushing the kernel.
In modern milling, a series of breaking, purifying, and reducing operations are performed. Each of these milling processes helps to separate endosperm particles.
The degree of this separation determines the texture and cleanness of the flour produced.
Conditioning of Wheat Before Milling
Conditioning of wheat, or tempering, is the process of preparing the grain for milling.
In this process, a controlled amount of water is added to the wheat and allowed to rest for a period of time. The goal is to allow the water to penetrate the entire kernel and improve the behavior of the constituents of the kernel during the milling process.
Improper control of conditioning can have adverse effect on milling. Brittleness of the kernel, excessive loss of bran, and inefficient removal of endosperm are some of the adverse effects of improper conditioning.
Conditions of the wheat, kernel characteristics, moisture content, and needs of the milling system should be considered when determining what kind of conditioning is needed.
The Importance of Milling Gradually
One of the most critical aspects of producing quality flour is gradual reduction. Instead of grinding the wheat kernel to make flour in one step, the kernel is gradually opened and the endosperm is progressively reduced in particle size.
The first stage, known as the brake system, seeks to separate the kernel into different fractions, while keeping the bran in a larger particle size. Purifiers and sifters, along with other reduction system rolls, help to further classify the endosperm by physical characteristics. Once classified, the endosperm fractions can then be reduced to flour.
The gradual process of reducing the size of the endosperm to flour gives the miller control over the size of the flour particles and reduces the amount of germ and bran mixed in the flour.
The Effect of Particle Size on Texture of Flour
Particle size of flour is a crucial factor in determining how flour feels and how quickly it can hydrate. Finer flour particles allow for better and more even hydration, while larger flour particles take longer to hydrate and can influence the characteristics of the dough. However, flour can be ground too small. Extremely small flour particles can increase damage to starch. Damaged starch absorbs water differently from undamaged starch and can influence the behavior of the dough.
Therefore, the goal is not always to produce the smallest flour particles. The goal is to produce a particle-size distribution appropriate for the end-use of the flour. For bread flour, a balance of particle sizes may allow dough to rise properly. In cake and pastry flour, a more uniform smaller particle size may be an advantage
Controlling Damaged Starch
A major component of the wheat endosperm is starch, and the physical condition of starch impacts flour performance.
Damage to starch occurs during the milling process. While some damaged starch can benefit dough performance by allowing water to be absorbed more readily, it can also create sticky dough and negatively impact other baking performance.
The impact is dependent on the flour’s application. Other characteristics of the flour may help offset problems associated with damaged starch. Therefore, the objective of the milling process should be to arrive at the desired level of damaged starch and not to either completely minimize or maximize it.
Protein and Gluten Development
Dough performance is impacted by the quantity and the quality of proteins present in the wheat endosperm.
Flour proteins participate in the formation of the gluten network that gives the dough elasticity and the capacity to hold gases, especially important in leavened products like breads. Protein quantity is important, but the quality of the proteins may also impact performance.
The performance and quality of flour can best be impacted by balancing the functionality of proteins and starch through appropriate selection of wheat and milling.
Flour Texture for Different Applications
The texture of flour varies for different end products.
Bread Flour
For bread, the flour has to develop a strong and extensible dough. The flour has to be able to take up water and form gluten.
The properties of the flour such as the conditions of starch and protein, and the particle size distribution, affect the performance of the flour.
Cake Flour
For cake products, the flour should not develop too much gluten. A tough cake is undesirable.
For these products, the flour should be from a softer wheat, and be finely milled.
Biscuit and Cookie Flour
Depending on the product, the flour for cookies and biscuits should be of a certain protein level for gluten development.
A lower level of protein may give a crisp or tenderness in the end product.
Particle size and water absorption affect the handling of the dough and the finished product.
Pasta and Semolina
Durum wheat is distinctively hard and has a coarse and uneven endosperm, and is generally used for products like pasta and semolina.
The desired characteristics of this flour are very different from bread or cake flour.
Ash Content of Flour
Ash content of a flour can indicate the mineral content of the flour and how much the bran has been removed. Generally, the bran has a higher mineral content than the endosperm. Therefore, a flour with higher ash content may be contaminated with some bran.
While ash does not relate directly to flour texture, it can be used to assess flour streams and efficiency of the milling process.
In the production of refined flours, keeping the ash content of the flour within specification aids in maintaining product color and consistency.
Bran Contamination and Flour Texture
Even trace amounts of bran can influence the behavior of flour.
Bran particles contain fiber and can disrupt the continuous formation of the gluten network. Bran can also absorb water and disrupt the structure of the dough.
For whole wheat products, the intention is to retain all parts of the kernel, and therefore, interaction among bran, germ, endosperm, water, and gluten must be adequately managed.
In the case of refined flour, the intention is to completely remove the bran from the endosperm to obtain a smooth flour.
Improving Flour Through Sifting
Sieving is a primary means of size reduction of flour particles.
After grinding, the flour or intermediate product contains particles of different sizes. The sifters remove the larger particles, and the material that moves through is directed to the desired flour stream.
Depending on the configuration of the sifters, millers can obtain different particle-size flour profiles for a given product.
Purification of Endosperm Particles
The intention of the purification systems is to improve the separation of bran from endosperm and allow millers to obtain a better control over particle size of the flour particles.
Efficient purification can result in a higher flour yield and help to maintain the color and quality of the flour.
Poor separation results in either too much bran or endosperm loss.
Therefore, purification is an important step to achieve the required texture of flour from the structural components of the wheat kernel.
Moisture and Texture of Flour
Wheat moisture influences kernel hardness and wheat endosperm breakage. Moisture also affects the brittleness of the coat and inner layer of the kernel.
After milling, the moisture content of flour influences its quality and the ease of processing and handling.
Flour should be milled to a specific optimal moisture level to achieve consistent performance. The purpose of monitoring and controlling moisture during the flour-milling process is to produce consistent flour.
Several factors can contribute to natural variation among flours. Millers take advantage of variations by blending wheat or flours to achieve a particular specification.
For good baking performance, particle size distribution, and color, the ash and protein content of flour should be balanced. Achieving the ideal balance often helps make up for any deficiencies that single lots may have.
Flour stored for long periods can lose its baking quality. Moisture, temperature, insects, and odors adversely affect flour quality during storage.
Storage conditions should protect flour from adverse effects of time to preserve the desired qualities established during the milling process.
Good stock rotation also ensures a reliable supply of the best flour quality.
Testing Flour Texture and Performance
Flour texture can vary, and the eye test alone cannot determine desired texture.
Professional texture testing of flour may include evaluation of the following:
- Moisture
- Protein
- Ash
- Particle size
- Gluten
- Water absorption
- Starch damage
- Falling number
Dough and baking performance
Additionally, the flour’s performance can be assessed as to whether it helps produce the desired end product. In an industry setting, performance tests conducted in the laboratory can help manufacturers set targets and define variations in flour before it is used in production
How to Improve Flour Texture Step by Step
Improving flour texture can be done by taking a step-by-step approach throughout the milling process.
Step 1. Define the Final Product
The product the flour is used to produce determines a lot of requirements.
For example, the texture of flour used to make bread will not be the same as that for flour used to make cakes, crackers or pasta.
Step 2. Choose Appropriate Wheat
Wheat that is appropriate for making the desired end product is chosen.
Step 3. Clean the Grain
Any foreign materials and impurities are removed.
Step 4. Condition the Wheat
Wheat is adjusted to the right moisture and tempered for the right time, based on its characteristics and the objectives of milling.
Step 5. Break System
The kernel is opened progressively to release endosperm without unduly pulverizing bran.
Step 6. Purify Endosperm
The endosperm is separated from bran and germ.
Step 7. Control Reduction
Endosperm is reduced to the desired size of flour particles while minimizing damage to starch.
Step 8. Sift and Classify
Use appropriate sieves to control particle-size distribution.
Step 9: Blend Flour Streams
If necessary, blend different streams of flour to reach required specifications.
Step 10: Test the Finished Flour
Check if flour meets physical, chemical, and functional requirements.
Potential Problems that Reduce Flour Texture Quality
There are several errors that can occur during processing that negatively impact flour texture.
Excessive Grinding
Excessive grinding may damage starch and adversely affect flour behavior.
Poor Wheat Conditioning
Tempering incorrectly may not properly separate bran from endosperm.
Excessive Bran Contamination
Bran is large enough to affect mouthfeel, color, and hydration.
Inconsistent Particle Size
Distribution of various particle sizes can adversely affect flour’s ability to absorb water and negatively impact the processing performance of the flour.
Poor Storage
Flour quality can be adversely impacted by moisture, pests, heat, and contaminants.
Inappropriate Wheat Selection
Even the most excellent milling cannot fully compensate for poor quality wheat.
How Modern Milling Allows for Greater Endosperm Recovery
Modern milling systems are designed to recover as much high-quality endosperm as possible.
The use of systems such as roller mills and sifters in series allows for controlled reduction in particle size. Purifiers assist in the separation of endosperm from the bran.
The use of automation to monitor moisture and the flow and grinding conditions of the flour, as well as the quality of the final product allows millers to adjust the grind as necessary to ensure consistent quality of the flour.
With the use of controlled mechanical processing along with the use of laboratory testing to assess the flour, mills can ensure their flour has the necessary qualities to produce good quality baked goods.
The Relationship Between Endosperm and Mouthfeel
The endosperm determines the characteristics of flour that ultimately determines the texture and mouthfeel of foods produced from it.
The size of flour particles and their other characteristics impacts the texture of the final product. The quality of flour also affects how the flour interacts with the other ingredients during the baking process.
A finely milled flour will produce a smooth batter and a smooth texture in the final food. Flour that contains particles of various sizes will produce a different texture in the final food.
Different types of flour can be used to make breads of different texture and mouthfeel, and cakes with varying tenderness.
Wheat Endosperm and Water Absorption
The characteristics of wheat endosperm determines a flour’s ability to absorb water.
Other characteristics of flour such as damaged starch and fiber also contribute to the water absorption properties of flour.
Flour with high water absorption will result in a dough that requires less water to make and will be easier to work with, compared to a flour with lower water absorption.
The aim is not to achieve the maximum level of water absorption. The target should be to attain the correct level of hydration for the product.
Higher predictability of water absorption can be achieved by having better control over starch damage and particle size.
Principles for Better Flour Texture
There are practical principles that flour product manufacturers can rely on to produce consistent quality:
Use suitable wheat. Quality of flour is a direct reflection of the quality of the wheat.
Adjust wheat moisture content. Appropriate and uniform conditioning of the wheat is critical.
Control grinding time and temperature. Prolonged grinding of wheat results in excessive damage of the starch and consequently substandard flour.
Starch damage. Keep it within a suitable range for the product being manufactured.
Particle size. Inconsistent particle size results in a low quality flour product.
Unwanted bran and germ contaminations. This is especially important for refined flour.
Use flour blending. Blending can be employed to compensate for natural variations in wheat.
Test flour. Regulate flour quality by laboratory tests.
Storage. Protect from pests, moisture and extreme temperatures.
Evaluate flour in the final product. The ultimate test of the baking quality of flour is the baking performance in the final product.