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The Science of Gluten Proteins – Bread vs Scones
Tried making light and fluffy wheat-free bread? Or accidentally over-kneaded your scones? If so, you’ve ‘met’ a unique group of proteins: gluten. These molecules can form amazing, elastic networks. We’ll have a look at how and when they do so!
When making bread, recipes will often tell you to knead your dough to ‘develop’ gluten. ‘Activating’ the gluten should help create a flexible, and light and airy dough.
Recipes for scones on the other hand, call for the exact opposite! They tell you not to ‘work’ the dough. For fear of developing these same gluten proteins!
So why do we sometimes want these gluten networks, and other times not so much? To understand, we’ll take a deep dive into gluten. These proteins show some fascinating chemistry!
What are gluten?
Gluten are the main proteins in wheat, making up about 85% of the overall protein content. When using wheat flour in baking or cooking, they play a crucial role in how your final product turns out.
The protein content of a flour is not necessarily the same as the gluten content of that flour. Also, keep in mind that different species of wheat can contain a different fraction of gluten, it is not always exactly 85%.
A refresher on proteins
Recall that proteins are made up of long chains of amino acids. You can consider each amino acid to be a ‘bead’ in a protein ‘chain’. Each protein has a different chain of amino acids.
There only exist a limited number of amino acids, a little over 20. Each amino acid has the same core backbone which allows them to link together. Attached to that backbone you will find a group of atoms, we’ll call them the side-group. These side-groups are unique to every amino acid. They determine the behavior of that specific amino acid, and its role in the overall protein.
Gluten are proteins, long chains of amino acids
Gluten is not just one protein
Contrary to what you might have expected, gluten isn’t just one protein. Instead, it is a mix of proteins, consisting of two groups of proteins:
Both groups again consist of several different proteins. Their sizes and composition may vary slightly, but they do share a lot of similarities. Both gliadins and glutenins contribute to the unique role gluten play in foods.
Gluten’s unique property: network formation
So what makes gluten so unique and important? It’s their ability to form a flexible, elastic network, under the right conditions. This network can be stretched and pulled. It can even bounce back a little.
When using wheat flour, it is important to be aware of this characteristic. Sometimes you want the network to form, other times not so much!
Why do you want a gluten network?
So why would you want a gluten network to form?
Make it stretchy
Well, this network is what makes your dough stretch. It’s what allows you to pull it, or roll it into a (very) thin sheet without it breaking – e.g. for philo pastry or apple strudel. It’s what allows pizza makers to throw their pizza dough into the air, stretching it as they go!
If you’ve ever made corn tortillas, or papadums, you will have noticed that those doughs can’t be stretched. They don’t contain wheat, so there’s no gluten to give the dough this stretch. Instead of stretching, these doughs will break. Rolling them requires a slightly different technique than a wheat based dough.
Make it airy
When you bake any yeast-based bread, the dough needs to be proofed. During this time, the yeast in the dough ferments and forms gas. This expands the dough. The flexible gluten network is a key enabler of this behavior. It enables the dough to hold onto the gas bubbles. It ensures the dough can stretch and extend to accommodate the newly formed gas bubbles.
These gas bubbles make the dough light and airy, and ensure the final bread doesn’t turn into a solid brick.
How do gluten form an elastic network?
So how do these gluten proteins form this important elastic network?
Recall that proteins are long chains of amino acids. Each of these amino acids has a different ‘side-group’ sticking out of the chain. These groups of atoms can interact. They can attract or reject one another. They can form strong or weak bonds.
These interactions between the amino acids in gluten create the gluten network. A few types are especially important:
An important amino acid in gluten proteins is cysteine. The side-group of cysteine contains a sulfur atom. When two cysteine side groups meet, these sulfur atoms can form a bond, called a disulfide bridge. They link together. This connection is quite strong.
Glutenin connect with each other (intermolecular)
Both glutenin and gliadin contain cysteine amino acids. In glutenin proteins a lot of the cysteine is located towards the ends of the protein chains. It’s why it’s very easy for the cysteine amino acids from different proteins to react with one another. This way, they can form a large connective network of long protein strands. Since the connections are made at the end, it’s flexible and elastic.
Gliadin bonds within (intramolecular)
In gliadin, on the other hand, these cysteine groups are located throughout the protein molecule. As a result, these bridges are mostly formed within the same molecule. They don’t react with other molecules.
It’s why gliadin doesn’t play a big role in the formation of the network. Instead, it serves as a ‘filler’ and does play an important role in the overall consistency (viscosity) of the dough. Without gliadin, glutenin’s network wouldn’t be a robust.
Electrostatic & hydrophobic interactions
Even though the disulfide bridges are crucial for forming a gluten network, they can’t do it alone. Other amino acids in the chain can also interact with one another.
For instance, amino acids that have a positive charge are attracted to ones that have a negative charge. These are electrostatic interactions.
Similarly, hydrophobic amino acids, those that do not prefer to sit in water, will group together. They all prefer to stay clear from water.
Both of these interactions aren’t as strong as the disulfide bridges.
Water is an enabler
All of these interactions wouldn’t be possible without the presence of water. It’s why a gluten network doesn’t exist in dry flour. Only when wheat flour and water are mixed can the gluten formation start.
Water enables the proteins to unfold and extend, in a process called hydration. Next, water enables the proteins to move and find each other.
Developing gluten – Kneading & Patience
Water & wheat flour are the only ingredients you need to make a gluten network. You then need to make sure the proteins actually manage to find each other and interact. This is where the importance of kneading, mixing, and resting comes into play.
By kneading and mixing the water + flour mixture, the proteins are encouraged to unravel and align. The movement encourages them to find each other and form bonds.
How much to knead for depends on various factors. Kneading by hand for instance is less intensive than kneading with a machine. It also depends on the ingredients you’re using. High amounts of salt for instance can slow down the formation of the gluten network. As such, the ideal kneading time can vary widely.
Too much & Things break down
It is possible to overdo it and break the gluten network down again. This happens if you mix for too long. First the electrostatic and hydrophobic bonds break down again. Later, even the newly formed disulfide bridges might break.
If you’ve ever seen warnings not to knead a bread dough for too long, this is why. Too much kneading will undo a lot of the hard work done to make the network.
Trade effort for time
Instead of using force – that is, kneading – you can also use time to form a gluten network. So-called no-knead breads are known for their long resting times, often 18-24 hours.
During the resting time, the gluten proteins do also form a gluten network. It is thought that the gas formed by the yeast helps the gluten to do so. The slight pressure of the newly formed gas bubbles is enough to orient and connect the molecules.
If you’ve ever left a pancake batter for too long you may have noticed that its consistency has changed. The effect of time on gluten is one of the reasons for this change.
Salt helps entanglement
Salt is very important for the flavor of bread. But, it also plays a more nuanced role for the formation of the gluten network. Salt prevents excessive repulsion of chains of amino acids and encourages proteins to approach each other. This way, it encourages entanglement. Depending on the style of bread you’re after, this may be either desirable or undesirable.
Salt gives a tighter, denser dough. It also takes longer for the gluten network to form. Though researchers still don’t fully understand how the impact of salt works!
Enzymes can help
To speed up the formation of the gluten network, you can also use enzymes. Enzymes are also a type of protein. They’re special proteins: they can catalyze, speed up, chemical reactions. They’re an aid to the molecules that want to react.
There are a lot of different types of enzymes. Every enzyme has its own specialty. The reaction it is best at catalyzing. Enzymes called transferases can help with the formation of the gluten network. They catalyze the formation of the necessary bonds between amino acids.
How to prevent gluten formation
Sometimes though, you don’t want gluten formation (more on those below). Luckily, there are also ways to prevent the formation of this network.
The first ways to do so are to do the exact opposite of what’s mentioned above:
- Do not knead or mix excessively
- Do not leave the dough to stand for long
But, there’s more you can do!
Fats blocks gluten
As we alluded to earlier, the gluten network needs water to form. The water enables the proteins to find one another. A way to block them from finding each other is by adding fat. Fat and water don’t mix. Fat can block the formation of disulfide bridges, as well as the electrostatic interactions from occurring.
It is why recipes for breads with a high-fat content that do need a strong gluten network, often tell you to add the fat towards the end, after kneading. This way, the gluten network can form, before the fat gets in the way.
Common examples of fats used in wheat products are olive oil, butter, shortening, but also egg yolks, which contain a reasonable amount of fat!
Sugar ‘steals’ water
Another way to limit the development of gluten is the addition of sugar. Small quantities won’t have an impact, but larger amounts limit the amount of available water. If less water is available, it will be harder for the gluten network to form.
When you do and don’t want gluten development
Last, but not least. Now that we know how a gluten network is formed and how to control it, let’s have a look at gluten in real life. We’ll come back to our bread and scones from the beginning of this article. They are on the opposite side of the scale for gluten formation. Why is that?
Do: Loafs of bread
Probably one of the most commonly mentioned examples of desirable gluten formation: a loaf of bread. Whether it’s a baguette, a whole wheat loaf or a basic white loaf, gluten ensure it’s light and airy.
It’s a lot harder (though not impossible) to make a gluten-free loaf that’s just as light and airy.
Do: Flatbreads & Pizza
A lot of flatbreads, as well as pizza, benefit greatly from having gluten in their dough. The gluten helps to make the dough stretch and pull. This enables you to create thin, rolled breads, that can puff up during baking. The flexibility of the dough is crucial here.
Of course, if you’re using yeast to leaven the dough, gluten is helpful as well. The gluten ensures the bread can actually hold on to all those newly formed air bubbles.
English muffins, paratha roti, babka, Msemen, apple strudel, they all benefit from gluten!
Help, the dough contracts again!
A disadvantage of gluten on the other hand is its tendency to stretch and pull back. If you’ve tried rolling out pizza dough or flatbreads, you might have noticed this. As soon as you lift that rolling pin, the dough contracts again. Again, this is the gluten network at play. You can luckily easily overcome this by resting the dough for a little while.
Gluten development is actually very important for a bread. Reason is that this gluten network has to hold on to the air in a bread. The gluten network is flexible enough to rise when yeast produces gas (carbon dioxide), but strong enough to keep the gas in so it stays nice and fluffy. The better developed your gluten are, the better it will form this airy structure.
You do not want a gluten network in scones. Scones are supposed to be crumbly and flaky. They should easily fall apart. A gluten network is the opposite of this. The network can actually make a scone tough and sturdy. The opposite of what you’re looking for.
Luckily, scone recipes are designed to not form this network, in two main ways:
- Rub in the butter first: most recipes tell you to rub in the butter (or other fat) into the flour before adding the moisture. This helps to ensure that the gluten proteins can’t find one another.
- Mix into it just comes together: once the water, or other liquid, has been added to the scones, you’re told to mix until the dough just comes together. It shouldn’t fall apart into crumbles anymore, but, you should definitely not knead it. Again, to prevent the formation of that network.
Flaky pie crusts use a lot of methods similar to those of scones. Again, you’re looking to prevent excessive gluten network formation.
Don’t: Cakes & Cookies
The next big group of baked goods using wheat flour that do not benefit from a gluten network are cakes and cookies. Again, these should be crumbly, fall apart (relatively) easily and do not need to hold onto a complex structure.
It’s why recipes for cakes and cookies also often warn you not to overmix. Luckily, most recipes do contain ample amounts of butter or other fats. This helps prevent that network from forming as well.
Next time you make bread, or some scones. Remember gluten and your product will hopefully turn out even better!
Emma Christensen, Kitchen Science: Demystifying Gluten, Mar-5, 2008, link
Science of Cooking, How does fat affect gluten development?, Jan-13, 2003, link
Nathan Myhrvold, Francisco Migoya, Modernist Bread, 2. Ingredients, 2017, The Cooking Lab, p. 302
Thomas A. Vilgis, Soft matter food physics – the physics of food and cooking, Rep. Prog. Phys. 78, 2015, section 5.3, 7.1-7.3, DOI: https://doi.org/10.1088/0034-4885/78/12/124602