Gluten

Understanding the formation of gluten and how to control gluten development is important for achieving right texture desired in your baked goods. But what exactly is gluten, and why is it so important? We will take a closer look in this article.

Gluten Formation

Flour contains two essential proteins, glutenin and gliadin, which are found only in the endosperm of wheat grains. When water is added to flour, these proteins combine to form gluten. This process requires thorough mixing to create a strong and continuous network that is both stretchy and strong, a property known as viscoelasticity. Glutenin can provide tenacity (strength) and elasticity, whereas gliadin provides extensibility (stretchiness).

In the gluten network, the largest glutenin molecules form the backbone, creating subunits. These molecules have looped structures that make gluten stretchy and flexible. As tightly linked subunits bond loosely with gliadin, larger gluten aggregates are formed, creating a tangled network of larger gluten particles. These are bonded together by both strong and weak bonds, where weak bonds can break and reform easily, particularly during mixing where they would reform around the surfaces of expanding air bubbles during proofing. The gluten particles would also interact with starch granules, fats, sugars and gum.

Dough maturity is achieved when the dough has the proper balance of strength and stretchiness so it can form a uniformly thin and smooth film without tearing. This is important as the dough would only rise properly during baking if the dough is mature, setting into a firm, rigid, and porous structure as moisture evaporates and starch granules gelatinise. Bakers often perform the windowpane test to test the maturity of the dough.

Gluten Requirements

• Yeast-raised baked goods

Yeast-raised baked goods require the most gluten, and it is crucial to achieve the right balance between glutenin and gliadin. If there is too much glutenin present, the dough would get bulky and would not stretch easily. As a result, the dough would be difficult to shape and would not rise well, forming low-volume loaves with a tight crumb. If there is too little glutenin present, the dough would be too soft and would stretch easily, rising well but failing to retain gases during fermentations. This means that it cannot hold its shape, leading to low-volume loaves with large air cells.

• Chewy textured baked goods

Baked goods with a chewy texture such as bagels and sandwich breads have high gluten requirement. This ensures that high-volume loaves with a fine crumb can be formed.

• Baked goods with low gluten requirements

Products relying on other structure builders, such as eggs and starch, require less gluten. This includes liquid shortening cakes which rely on the soft structure of gelatinised starch and sponge cakes with high egg content. Although pie pastry relies on gluten for structure, should have minimal gluten development to stay tender.

• Rustic breads

Coarse-grained rustic breads have large irregular holes which are produced from weak gluten that tears relatively easily. They are made with flour with a relatively low protein content and when excess water is added to the dough, leading to a coarser grain and thicker, crisper crust after prolonged baking time.

Controlling Gluten Development

To effectively control gluten development, we have to first understand the three main ways of gluten development which encourage the alignment and the bonding of glutenin subunits into a large cohesive network. The first method is mechanical dough development, which is essentially mixing. The second method is chemical dough development, using ascorbic acid and also other maturing agents. The final method is bulk fermentation and final proof.

There are numerous factors which contribute to gluten development:

• Type of flour

Wheat flour is the only common grain with the potential of forming a good amount of gluten. Soft wheats are low in proteins and contain proteins with poor gluten development properties. The low amount of glutenin for the amount of gliadin results in glutenin subunits formed being smaller in size. In comparison, hard wheats are high in proteins. There is a large amount of glutenin for the amount of gliadin so larger glutenin subunits are formed.

In rye, only a small amount of proteins form gluten. Whereas oat, corn, buckwheat and soy flours do not form gluten at all. So baked goods formed do not have good gas-retaining property or structure-building properties, resulting in a dense and compact product.

• Amount of water

Water hydration is essential for gluten development so altering the amount of water could have a significant impact. Water is often added as a part of other liquids, such as in milk and eggs. But liquid oil does not contain any water and would not increase gluten development. In pie and biscuit doughs, gluten tends to be not fully hydrated so gluten does not develop completely, forming baked goods that remain tender. However in cake batter, an excess amount of water is present so that gluten is fully hydrated. But why are cakes tough and chewy? That’s because water dilutes the proteins present, weakening gluten. Also, adding water to cake batters would not result in an increase in gluten development. 

• Water hardness

Water hardness is a measure of the amount of mineral such as calcium and magnesium in water. Hard water is high in mineral whereas soft water is low in minerals. As minerals can strengthen gluten, yeast doughs prepared from hard water can be too strong and elastic, making the dough too bulky and would not stretch when gases expand. However, doughs prepared from soft water can be too slack and sticky. Dough conditioners can be added to compensate for water that is too hard or too soft. Dough conditioners for soft water often contain calcium salts such as calcium sulfate which could increase the mineral content. Whereas dough conditioners for hard water contain acids which react with minerals, preventing them from interacting with gluten. Alternatively other ingredients or processes can be adjusted to compensate for non-ideal water mineral content. For example if hard water is used, more water can be added to the dough to dilute the gluten and to slacken the dough. Less mixing and using a softer flour could also reduce gluten development.

• Water pH

The ideal pH for maximum gluten development is 5-6. To alter the pH, acids could be added to lower the pH whilst alkali could be added to raise the pH. Common acids added include cream or tartar, fruits, fruit juice and vinegar, making dough more extensible and easier to stretch without tearing. Alternatively, fermentation would lead to acid production. Baking soda is usually added as an alkali, forming a porous crumb which allows moisture to evaporate more easily, forming a crisper crumb. As baking soda also raises the set temperature of gluten and egg proteins, adding baking soda could allow more time for cookies to spread. 

• Mixing and kneading

Mixing and kneading can promote gluten development. They can speed up hydration by exposing new surfaces of flour particles to water. They would also incorporates oxygen from the air into dough, oxidising and strengthening gluten. In addition, mixing distributes particles evenly throughout the dough, forming a strong and continuous gluten network. When mixing, gluten strands align in the direction that they are mixed. However, if all gluten strands are aligned in the same direction, the dough would shrink in the direction that the gluten strands are oriented. Hence, the dough must be turned 90° with every knead. If the dough is over-mixed, excess gluten development could result in the dough being toughened.

Dough Relaxation

Allowing dough to rest reduces stress on the gluten strands, making the dough easier to roll and shape and less likely to shrink during baking. This is because the dough becomes more stressed the more it is stretched and worked, relaxing would therefore allow the gluten strands to adjust to the new shape and will not bounce back before baking. If the dough is refrigerated during resting, fats would solidify allowing for better lamination and flakiness.

Relaxation time varies for different types of dough. Bread dough should be relaxed for up to 45 minutes, whereas softer and slacker doughs such as pastry dough relax in less time. Pie pastry dough should be rested for at least several hours. As they contain very little water to keep gluten development at a minimum, it is important to allow time for water to distribute itself evenly throughout the dough. If water is not mixed in properly, the dough would be crumbly in some spots and soggy in others. In comparison, if dough is mixed thoroughly, gluten would over-develop.

In conclusion, understanding the chemistry behind gluten formation and development can have a significant impact on your baking results. By controlling different factors affecting gluten development and relaxation times, you can achieve the desired texture and structure for a wide range of baked goods.

Reference

• Claire, J.B. (2014) The Chemistry of Baking. Senior Thesis. University of South Carolina. Available at: https://scholarcommons.sc.edu/senior_theses/23/ [Accessed 2^nd January, 2024]
• Figoni, P.L. (2010) How Baking Works: Exploring the Fundamentals of Baking Science. 3^rd ed. Providence, Rhode Island: Wiley.