Cookie Science 13: The deal with gluten
This article is one of a series of Experiments meant to teach students about how science is done, from generating a hypothesis to designing an experiment to analyzing the results with statistics. You can repeat the steps here and compare your results — or use this as inspiration to design your own experiment.
To make a gluten-free chocolate chip cookie, I started by taking out the gluten. But these cookies baked up wide and flat. More importantly, people said they didn’t taste as good as a normal chocolate chip cookie. So now I’m on the prowl for something that will restore the taste and other missing properties to my gluten-free treats.
But what and how much of it should I add to my recipe? For answers, I turned to science. Well, to scientific papers, anyway.
These reports record the details of experiments that scientists have conducted. I’m hoping to get ideas from scientists who tried similar experiments and then learn from their results. I also want to learn more about gluten, what it does and what ingredients I might need to replace it.
You don’t have to read scientific papers, of course. But if you don’t learn from others’ research and mistakes, finding answers might require a lot more trial and error on your part. You may waste a lot of energy redoing what other people have already tried. So I headed for the library. A virtual library. All the papers I turned up could be downloaded from various sites, though many of them required me to pay for access (as I described in my last post in this series).
I have included a list at the bottom of this post under “further reading,” so that you can see exactly which papers I read.
Gluten: What’s it good for?
Gluten is a type of protein. Proteins aren’t just something you find in a steak. They are part of every living organism. Indeed, they are the chemical building blocks that make up cells and perform much of the work inside them. Proteins can have very different shapes and jobs. Some can be quite complex, with lots of smaller proteins playing some role in the work of a large protein. Gluten is actually made from two main proteins linked together: glutenin (GLU-tuh-nin) and gliadin (GLY-uh-din).
In plants such as wheat, these proteins serve as holding bins. All proteins are made of amino acids. Those tiny molecules are made of atoms, including carbon, nitrogen and sulfur. These elements might be hard to come by when a wheat seed first starts to grow. So wheat stores some of these elements in its proteins, such as glutenin. Later, when a seed needs more carbon or nitrogen, it can break down glutenin, using its building blocks to grow and eventually to make more wheat.
Just add water
A glutenin protein is a long chain of amino acids. Gliadin is round. In wheat plants, these two proteins aren’t linked to each other. But when wheat is ground into flour and mixed with water, glutenin and gliadin do join up. Together they form gluten. In bread dough, it provides a matrix-like structure — a pattern of proteins and the spaces between them. Being stretchy, this matrix gives dough its elastic texture.
The pattern gluten forms in water becomes important when you add yeast to bread dough. Yeast are single-celled fungi. They eat carbohydrates, such as the sugar molecules found in wheat. As the yeast digest that sugar, the chemical reactions the cells use to break it down produce carbon dioxide. The yeast then burp out this carbon dioxide as waste. In bread dough, the gluten matrix traps the carbon dioxide in little bubbles. Over a few hours, bread dough rises and becomes plump, filled with carbon dioxide. Without gluten, the carbon dioxide that those yeast produce would simply escape into the air. Then the bread wouldn’t rise and you’d get a dense, crumbly loaf.
Cookies, though, do not include yeast. So the gluten matrix in them serves another purpose. It makes a cookie’s dough springy. As cookies bake, they spread out on the baking sheet. Heat in the oven melts the fats and sugar in the dough. This makes the dough more fluid so that it spreads out. Gluten in the cookie dough forms a matrix which helps hold in the melted fat and sugar. This stops the cookie from spreading too far. The gluten also helps dough hold water. So cookies with gluten can be round, soft and chewy.
Removing gluten makes cookie dough less springy. So the cookies spread as they bake. And then they spread some more. This is why my gluten-free cookies in the first experiment were so much wider than wheat-based cookies.
Putting a spring in your dough
When bakers make gluten-free cookies, they need to add back the springiness. To do this, they substitute one or more other ingredients. Many people add chemicals called hydrocolloids. Colloids are materials in which undissolved particles spread out within a large volume of some other substance. The “hydro” in these colloids means that the substance the colloids are spread in is water. These molecules are polymers, long chains of repeating groups of atoms. The hydrocolloids used in baking are long chains of some sugar or starch molecule. Some of these polymers have long complicated names like this nine-syllable tongue twister: hydroxypropyl methylcellulose. Others have simpler names such as locust bean gum, guar (gwARR) gum and xanthan(ZAN-than) gum.
All of these hydrocolloids are attracted to or dissolve in water. Scientists describe this as being hydrophilic (or water-loving). When bakers add these molecules to dough, the hydrocolloids help to keep water in the dough. That lets the dough bake into a softer cookie. The polymers’ long chains also make the dough springy. As with gluten, this could stop a cookie from spreading too much as it bakes.
So I’ve decided to try adding a hydrocolloid to my gluten-free dough. Some grocery stores sell xanthan gum and guar gum, especially if the stores have a gluten-free aisle. Many gluten-free recipes call for xanthan gum. Some research studies I read about also used it. So I’ll try adding this hydrocolloid.
The dose makes the cookie
So how much xanthan gum should I add? Some recipes tell me to add a teaspoon. Others instruct me to add two. One I found says to add only a quarter of a teaspoon. I want to make a cookie as much like my control cookie as possible. Since I am not sure which amount will make a cookie most like my control, I’ll trying varying amounts in my gluten-free cookies. Then I will compare them to gluten-free cookies without xanthan gum, and to my control cookie with gluten. This type of testing is called a dose-response experiment. Here a scientist tests many doses of some substance to learn how it affects a result.
Now, it’s time to get back in the kitchen!
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(for more about Power Words, click here)
amino acids Simple molecules that occur naturally in plant and animal tissues and that are the basic constituents of proteins.
atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
carbohydrates Any of a large group of compounds occurring in foods and living tissues, including sugars, starch and cellulose. They contain hydrogen and oxygen in the same ratio as water (2:1) and typically can be broken down to release energy in the animal body.
control A part of an experiment where nothing changes. The control is essential to scientific experiments. It shows that any new effect must be due to only the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that give scientists something against which they can compare their experimental data.
colloid A material in which tiny insoluble particles are spread throughout a larger volume of another substance. Colloids take many forms. Smoky air is a colloid. So is fog. Milk is a colloid, with tiny globs of butterfat suspended throughout the liquid. Whipped cream is a colloid too. Colloids typically don’t separate into their individual components over time.
dose-response A type of experiment in which a scientist tests several amounts, or doses, of a particular variable — such as stress, a new chemical, or exercise — on a response. Responses could be everything from mouse behavior to how much cookies spread during baking.
gliadin A protein that forms a network with another protein — glutenin — to form gluten, a protein network that holds in moisture and gas in baked goods.
gluten A pair of proteins — gliadin and glutenin — joined together and found in wheat, rye, spelt and barley. The bound proteins give bread, cake and cookie doughs their elasticity and chewiness. Some people may not be able to comfortably tolerate gluten, however, because of a gluten allergy or celiac disease.
glutenin A protein that forms a network with another protein — gliadin — to form gluten, a protein network that holds in moisture and gas in baked goods.
hydrocolloid Long chains of a substance suspended in water.
hydrophilic Strongly attracted to (or readily dissolving in) water.
polymer Substances whose molecules are made of long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).
proteins Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better known, stand-alone proteins. Medicines frequently work by latching onto proteins.
variable (in mathematics) A letter used in a mathematical expression that may take on more than one different value. (in experiments) A factor that can be changed, especially one allowed to change in a scientific experiment. For instance, when measuring how much insecticide it might take to kill a fly, researchers might change the dose or the age at which the insect is exposed. Both the dose and age would be variables in this experiment.
xanthan gum A hydrocolloid made by the bacterium Xanthomonas campestris. It is a long-chained polymer often used in baking to make substances more elastic.
yeast One-celled fungi that can ferment carbohydrates (like sugars), producing carbon dioxide and alcohol. They also play a pivotal role in making many baked products rise.