Years ago as I stepped into the world of pastry I didn’t understand gluten as much as I do now, but even then, gluten had a bad reputation. Everyone was talking about how bad it is for your health and more and more people around me began talking about the health problems they developed after eating gluten. But as with most things, few people really understood what gluten really was and its importance in certain parts of pastry and moreover in bread making. So whether you avoid gluten or can’t get enough of it (I hear ya’, bread loving friends), I believe it’s important to understand how gluten works and what it is, why some products have lots of it and other don’t.
This article is part of a new series on the blog – Baking Science – that aims to shed light on the science behind baking, on the tools we use or the techniques we try to master, on spices and ingredients themselves.
Gluten is a network of proteins found in wheat products
In bread making, gluten is crucial because it plays the role of a net holding everything together. Imagine that amazing texture or ciabatta for instance – without gluten, those large air pockets would not be able to develop at that extent. Gluten traps the gas bubbles developed during fermentation of the bread dough, thus giving the bread its specific texture. And even though bread has ingredients that can be found in cakes, cookies or travel cakes as well, think of the texture these products have and compare it with the texture of bread. Due to gluten, the bread has an airy chewy, very satisfyingly texture. Now try to imagine a chewy cake or a cupcake – you would not want to eat it, I assure you!
How gluten works
Gluten is formed when two of the wheat’s proteins, glutenin and gliadin, come in touch with water. By water however, I mean not just the liquid itself, but other ingredients that are used in baking and contain water more or less, such as eggs, milk, heavy cream, sour cream… even butter has 82% fat, but the rest is water. When the above mentioned proteins come in contact with water, gluten begins to form inevitably, no matter what movement we add to the mix and I find this remarkable.
Adding water to flour starts the chemical process and mixing it improves gluten development, but mixing is actually not crucial to form gluten. Mixing is important mostly because it speeds up flour hydration and ensures the water is fully dispersed throughout the flour. When hydrated, the two proteins, glutenin and gliadin, bind together and form gluten. Curiously enough, if you take a piece of elastic bread dough and wash it over the sink, allowing water to run through it, starch will be washed out and what;s left behind is gluten. So gluten does have a face – it looks like a net, elastic and sticky. Each protein has a different role – glutenin, apparently one of the largest proteins ever identified, contributes to the strength of the dough, forming strong, stretchy units of molecules; gliadin allows the dough to flow like a fluid, contributing to the ease of working the dough. The more proteins a flour has, the more water it needs to hydrate and this makes sense now if you think of the information above.
Hydration of flour happens quite quickly, but gluten development takes time (not necessarily kneading though, keep this in mind!). It takes time to form the chemical attachment that bond gluten proteins together into a strong network. As mixing goes on, the proteins bind more and more, forming at first short strands of gluten, then longer strands of gluten, finally becoming a real network. The gluten network that eventually forms has two important characteristics:
- elasticity – the ability to stretch
- extensibility – the ability to hold shape
Without these two properties, bread making and bread itself would be flat, crumbly, dense and less chewy so it would basic not have all the things that we love about bread.
Interesting enough, gluten development does not stop when you stop mixing the dough. It actually continues to form and become stronger in some cases or more complex up until the dough is proofed. Enzymes that help gluten develop have time to act as the dough rests and begins to ferment due to yeast. Those gluten strands mentioned earlier become longer and stronger as more molecules stick together. One thing that bread makers do is periodically fold and stretch the dough to help align its gluten strands into a beautiful network. This network will later give the dough the perfect texture and the capacity to expand and hold its shape as the carbon dioxide is produced by the yeast or the dough is worked furthermore into loaves or other shapes and then baked.
It’s interesting to see how gluten relaxes when the dough rests and how it’s reactivated when the dough is shaped or worked once again. When working a piece of dough that has good gluten, but it has been resting a certain amount of time, gluten strands tighten and reorganize once again, creating a certain tension in the dough. This tension can easily be noticed in a fresh dough that is so elastic that it cannot even be rolled into a thin piece as it has the tendency to shrink back to its original size or shape.
Gluten traps gas bubbles in its complex network, helping the dough rise during fermentation. But the largest increase in volume can be seen during baking when the dough nearly doubles in volume. So the dough rises at least two times – one time when fermenting the the bowl and the second time at the beginning of the baking time as the temperature rises and the yeast warms up. To expand during both processes, the dough must be strong enough to retain the gas the the yeast produces. Imagine those air bubbles trapped in the gluten like tiny air balloons – once the temperature in the oven rises, these air bubbles expand even more. If the gluten is strong, it will hold its shape, but if it’s not or the gas (carbon dioxide) exerts more pressure than the gluten can withstand, the complex network weakens, releasing the gas and deflating the dough.
How to develop gluten
Gluten development starts with one crucial step – choosing the right flour for your application. If we are talking about fermented products, such as bread or brioche, we know for sure that we need a complex structure to have a good and strong dough, therefore we are going to give these doughs the best chances we can to develop the right texture, thus choosing a flour that has a high content or protein. This can easily be assessed by reading the labels found on each bag of flour at the supermarket and choosing the highest protein of white flour we can find. Usually for bread and other products that means something between 12 and 15% protein. Do not be mistaken by whole wheat flour which has a high protein amount, but it also has bran and germ which chemically and physically affect gluten development. Various things happen: the bran and germ absorb most of the water quickly, leaving the protein not hydrated enough, while the excrete compounds that weaken the gluten, creating wholes in its structure.
Keep in mind that wheat is the main grain that has protein that form gluten. Other types of grains have very little proteins and some don’t have at all. For instance, rice and corn cannot form gluten at all, even tough they do contain other proteins. Rye is special because it does have a bit of gluten, but not enough to form the same texture as wheat does. Rye becomes bread relying on pentosans which are polysaccharide molecules that form a sticky gel when mixed with water.
Another important factor when developing gluten is the water added. Too little water won’t hydrate the flour enough, too much water can cause problems, especially for those who are not experimented bread makers, since the dough has a looser texture and it’s more difficult to shape it.
One interesting aspect of bread making is the addition of salt and this can be found even in pastry – for instance choux pastry. Salt strengthens gluten strands bonds. The gluten proteins naturally repel one another, but the chloride ions in salt pushes them to overcome the natural repulsion and stick together. You can see a change in the dough even if you add it later – as the salt mixes in and dissolves, the dough slowly firms up. Salt also helps regulate the fermentation process so its addition at the beginning or end of the mixing process can be crucial sometimes.
Fats however are the opposite of salt, slowing down gluten development by coating the protein strands. For this reason, rich doughs like brioche call for longer mixing times. The fat coating acts like a barrier, stopping proteins from being properly hydrated and bond with each other. To prevent this from happening, in these type of dough, fat is added later on, as we begin to see some network development. One special case is shortdough or pate sucree where the fat is added at the beginning precisely with the purpose of coating the proteins and preventing them from hydrating and forming gluten.
Sugar and gluten are not great friends either because they fight for water. Sugar is hygroscopic, meaning that it attracts water to its molecules. Therefore in doughs with a high sugar content, gluten development happens at a slower rate than bread recipes where the main ingredients are water, flour, yeast and salt.
Time is a great tool for gluten development as well. Following the same line as we just did, we can tell that the longer the flour and water spend together during the hydration process, the more gluten strands form. Time also allows enzymes intervene in gluten development and time is crucial for fermentation as well.
What type of flour to use
The protein content in flour is a good indicative when choosing the right flour for your application, but at the same time, this analysis may or may not be right because a high amount of protein does not mean that specific protein is a good quality one. While gluten development and protein content are strongly connected, there are situations in which the protein content does not mean a good quality flour and a great gluten after mixing:
- Growing conditions of wheat
- Wheat variety
- Flour blends
- Heat damage
- Bug damage
- Enzymatic additions
The rule I go by when baking is choosing a high protein flour for my breads and sweet doughs, a low protein flour for cakes and other products that need to be fluffy and a medium protein content for products such as shortbreads, cookies, travel cakes. But more on flour to come!