Background Content
History of the Use of Yeast in Breadmaking
Yeast has been used to help with the leavening of bread for thousands of years at first incidentally and then throughout time more purposely as people started to realize what was occurring. Breadmaking has not been the only use of yeast by people throughout history as it has also been used in the making of alcoholic drinks as well. Through this background you will see the connection these beverages have with the evolution of breadmaking. But to understand how yeast has been used throughout history, we first have to answer the question: What is yeast?
What is Yeast?
Yeast is a single-celled living microorganism that falls under the fungi kingdom. Yeasts are considered eukaryotic microorganisms, meaning their cells have a nucleus containing their genetic material, not so different from human or animal cells.[1] Unlike humans and animals, however, yeasts reproduce asexually through a process called budding, a process where a new cell forms an outgrowth from the parent cell.[2] The most known species of yeast is Saccharomyces cerevisiae, also known as baker’s or brewer's yeast.[3]
Yeasts feed primarily on simple sugars such as glucose and fructose and break them down to harvest energy. This process can occur in two ways: aerobic respiration and fermentation. Aerobic respiration is the process or yeast digesting sugars when oxygen is present, allowing carbon dioxide and water to be released. Over time oxygen levels will drop and the process of fermentation begins, now releasing alcohol and more carbon dioxide as sugars are broken down.[4] This fermentation process is what people have used to make beer and wine and eventually leavened bread. In bread, as carbon dioxide is produced it gets trapped within the dough, creating air bubbles allowing the bread to rise. While this unit will be focusing on baker’s/brewer’s yeast, there are nearly 1,500 species of yeast.3 These species range from ones that can cause infections in people to others can be quite beneficial, aiding in production of life-saving medicines and even biofuels.[5]
When was yeast added to bread?
Bread has been a staple in the human diet for hundreds of generations, but it was not until later that yeast was brought into the fold when making bread. The consumption of flatbread can be dated back to the late Stone Age in parts of the world where grains were part of the main diet.[6] It was not until the Egyptians, around 400 BCE, we found evidence of leavened breads.6 However, this was not the process of intentionally adding yeast like we do today. Instead, it was wild yeast in the air that would infect and feed on the sugars of a dough that was left out. As time passed, bread makers began to use leftover pieces of dough, where yeast was already present, to help raise new dough. Yeast production had become so important that even became a specialized profession in Egypt by 300 BCE.6
When did pizza come into the fold?
Pizza originated from Italy in the city of Naples as a working-class food that could be quickly eaten and was inexpensive. The word “pizza” is closely related to “pita” and has been referred to as such going back to the tenth century.[7] Neapolitan pizza uses a round yeast-raised crust that is stretched thin in order to make it have both a crisp and chewy texture. The crisp comes from the high temperature cooking in traditional brick ovens, and the chew comes from the gluten development when making the dough. A simple pizza at the time would have been topped with tomatoes, olive oil, garlic, and oregano.7
The more widely known “Pizza Margherita” was created for Italy’s Queen Margherita for her visit to Naples in 1889.[8] The three toppings consist of white mozzarella cheese, red tomato sauce, and green basil giving an homage to the Italian flag. Pizza would eventually make its way to North America via Italian immigrants between the late ninetieth and early twentieth century, creating the now popular “New York Style” pizza.[9] Fast forward to present time and pizza has become one of the most popular foods eaten in the United States.
It All Starts with the Dough
While pizza making techniques can be difficult to master, the actual dough itself, that is the base of this popular food, is made with few and easily accessible ingredients. A standard pizza dough consists of flour, water, salt, sugar, and yeast with the option of including a fat such as olive oil for flavor. What can be overwhelming for some people new to pizza making is in the options of those ingredients, specifically the type of flour and yeast as there are quite a few options which will yield different results.
Choosing a Flour
In pizza making, there are three different types of flour that can be used, and all have their own place depending on what a person will be looking for in the final product. Those flours are 00 flour, bread flour, and all-purpose flour. The differences in these flours are found in their protein content. For the use of the activities in this unit, we will be using bread flour. But to understand why, we should look at each type of flour and what sets them apart.
00 Flour is the traditional flour used when making Neapolitan style pizza. A flour of this type has a protein content that ranges from 11-12 percent.[10] This higher protein content means the flour will absorb more water than a low-protein flour, which will result in a stronger gluten network in the dough. Unfortunately, due to how fine this flour is milled, 00 flour needs a high temperature cook that would require a pizza oven for the best result.[11] Meaning this flour would not be the best option for the activity in this unit.
All-purpose flour is the most commonly known of the three flours and is a staple in most people’s homes, and it can be used for a vast amount of baking products. This flour has a lower protein content ranging between 7.5-9.5 percent.10 This means it will absorb less water and make a dough that does not have as strong of a gluten network as higher protein flours. Because of the low protein content, this flour is not the best for doughs that need to rise because there will be less gluten present to capture the carbon dioxide being given from the yeast. That said this dough can be used for same day pizza dough but again will not give the best result for our application.
Bread flour, as in its name, is typically used for bread and other baked products that require leavening. This is because of the higher content of protein present, ranging from 12-13 percent.10 Similar to the 00 flour, this higher protein content leads to a higher absorption of water which creates a stronger gluten network in the dough leading to a chewier final product. More gluten means more carbon dioxide being captured from the yeast, resulting in a higher rise in the dough, making this the flour of choice for the activities in this unit.
What is Gluten?
The weight of flour consists primarily of starch, but a small percentage of proteins are also present. That percentage, as you saw in the previous section, varies depending on the type of flour. It's these proteins that are the makeup of gluten. When the proteins are in their dry state, they are inactive but when given water they can change shape and form and break bonds with one another.[12] Most of the gluten proteins consist of gliadins and the glutenins. The gliadin chains fold into themselves, creating weak bonds with other gliadin and also with glutenin proteins, while the glutenins bond with each other to create a vast tight network.[13]
On the end of these chains are sulfur-containing amino acids that can have strong sulfur bonds with the other end of glutenin chains, while the coiled middle includes weaker bonds, such as hydrogen and hydrophobic bonds. These chains link end to end to form chains that can reach a few hundred glutenins long, and the coiled segments stretch to form temporary bonds with other gluten proteins, ending in a connected network of coiled proteins known by its more common name, gluten.13
Is that why the dough is so stretchy?
The gluten present in dough has both an elasticity (glutenin) and plasticity (gliadin) to it.13 This causes dough to change shapes with given pressure and allow it to resist and come back to its original shape when there is no longer pressure. These properties are what enables dough to expand when carbon dioxide is created from the yeast but not get too thin and break during the rising process. The gladins, because they are compressed, let parts of the glutenins slide past each other without creating bonds which gives gluten in plasticity, while the elasticity comes from the kinked and coiled structure of the chained gluten proteins.13
When a dough is kneaded, it unfolds and realigns the proteins, but there are still loops present along their chain links. Once the dough is stretched, the loops and kinks are straightened out, but once the pressure of stretching is discontinued, the molecules revert to how they were.[14] This is why in the activity in this unit it is important to let the dough rest before attempting to stretch it.
Why does the dough need to rest?
If you have even attempted to make anything with dough, you may have noticed how difficult it can be to stretch or create a desired shape right after kneading. This is because of the elastic characteristics of wheat flour doughs, but luckily if dough is given time to rest, that elasticity will relax over time. But how does this happen?
It comes back to the protein molecules; in a well kneaded dough, the protein molecules have been aligned and created many weak bonds. With so many bonds, proteins hold firm and resist being stretched creating a firm dough.14 This is why in pizza making bakers bring the dough together into a taut dough ball before resting. This physical tension of the ball shape slowly breaks some of the bonds because they are weak, allowing the structure to relax into a much more malleable dough.
Can We Control How Strong Gluten is?
Gluten strength can absolutely be controlled because not all baked goods benefit from a strong gluten network. While a strongly bonded elastic gluten is great for yeast-leavened baked goods, it would lead to undesirable toughness in other forms such as cakes and cookies, where a more tender product would be desired.14 There are quite a few ingredients and techniques bakers use to control the bonded strength of gluten, one of which was covered earlier in this unit when discussing the different types of flour. Some others include:
- Oxidizing substances (aging and improving substances) can increase the end-to-end linking of the glutenin, making the dough’s gluten network stronger.14
- The amount of water in the dough can influence how concentrated the gluten proteins are and how much they can bond to one another.14 Less water leads to a crumbly texture while more gives the dough a softer moister feel.
- Kneading (the process of pressing and folding dough into itself) can also affect the elastic network for the gluten proteins as the more dough is kneaded the stronger the network.[15]
- The presence of salt can strengthen gluten greatly; this is because the positively charged sodium and the negatively charged chloride ions cluster the charged glutenin proteins. Preventing those charged parts from repelling each other lets the proteins come closer together to form a stronger bond.15
- Sugar at a concentration of 10% or more of the flour weight can limit gluten development caused by its dilution of the proteins in the flour.15
- Fats can weaken gluten as well because it will bond to the hydrophobic (water fearing) amino acids along the protein chains preventing them from bonding to each other.15
- Last, acidity can weaken a gluten network by increasing the amount of positive charged amino acids running along the protein chains and increasing the repulsive forces between the chains.15
Why Does Yeast Work in Pizza Dough?
It all comes down to gas bubbles; this is what gives leavened doughs their light texture. Bread products such as pizza can be aerated to the point where as much as 80% of their volume is empty space.15 These bubbles weaken the gluten network and starch and divide dough into millions of thin delicate sheets where gas can be captured.
It’s a bit of a misnomer that yeast or other chemical leaveners are creating gas bubbles while dough is rising. These ingredients don’t create new bubbles. Instead, the carbon dioxide released from them is captured and enlarges the tiny buddles that already were there. These bubbles were created when the dough was kneaded and air was introduced. The more bubbles produced when the dough was prepared, the more tender the final product.[16]
The Chemical Reaction of Yeast in Dough
As overviewed earlier in the history of yeast section, people have been using yeast to leaven bread for thousands of years. People have used its production of carbon dioxide to add gas to help dough rise, but now we should dive deeper into the science that causes this to happen. The source of the yeast producing gas comes in its metabolism of sugar. When yeast metabolizes sugar for energy, it produces carbon dioxide gas and alcohol as by-products. This is considered a chemical reaction because the sugars are broken down into entirely new substances.
The chemical equation of this process that takes place in the yeast is: C6H12O6 -—> 2C2H5OH + 2CO2 (1 molecule of glucose yields 2 molecules of alcohol plus 2 molecules of carbon dioxide).16 During the dough making process, both carbon dioxide and alcohol are trapped within the dough and only released by the heat of the baking process.16 In an unsweetened dough the yeast will feed on the glucose, fructose, and maltose which enzymes in flour naturally produce from the broken-down starch.16 A small amount of sugar added (like what will be added in one of the activates) will increase the yeast’s reaction. Only a small amount will be added as if too much sugar is added it will decrease yeast activity as salt does.
The chemical reaction in yeast can also be aided by temperature. The cells grow and produce gas the best at about 95 degrees Fahrenheit or 35 degrees Celsius.16 Not only is the yeast producing gas to help the dough rise but also several other chemicals that affect the dough's consistency through strengthening the gluten network but also the taste of the baked good. But there is not only one form of yeast for baking and choosing the correct one (like flour) is important for having the best result in the final product.
Choosing a Yeast
When choosing a yeast for baking, there are three common forms: compressed yeast, active dry yeast, and instant dry yeast. Each of these forms is a different genetic strain of Saccharomyces cerevisiae just with different traits.16 Let's explore each to help understand which will be the best for the application of pizza dough making.
- Compressed yeast is a moist block of fresh and alive yeast cells and produces the most leavening gas of the three forms.16 Unfortunately, because it is fresh that also means it is perishable and must be kept refrigerated and even then, has a very short shelf life of one or two weeks. Which makes it not a great option for the use of this unit’s activity.
- Instant dry yeast is dried quickly and in the form of small porous rods that can take in water faster than active dry yeast. This means this yeast does not need to be presoaked before mixing with other ingredients and produces carbon dioxide vigorously.16 While this sounds great, this quick rise can cause structural concerns which can lead to stretching issues once the rise is over.
- Leaving active dry yeast as the best option for pizza making. This form of yeast is dried into granules with a protective coating of yeast debris that allows the yeast to stay dormant and can be stored for months at room temperature.16 When ready to be used the yeast is soaked in warm water before mixing the dough to bring it out of its dormant state. Because it ferments slower than the other two forms, it makes the dough much easier to handle and helps fill in gas bubbles more uniformly.
Pizza Dough: Mixture or Solution?
To answer this question, we must first establish what a mixture is compared to a solution. A mixture is a combination of two or more substances that come together while keeping their own physical properties.[17] Mixtures can fall under two categories: heterogenous or homogenous. In a heterogeneous mixture, the product is not uniform throughout, and sometimes the substances making the mixture can be recognized by the eye.17 Examples of this can include salad, cereal and milk, and chocolate chip cookies. This is compared to a homogenous mixture which is uniform and has no differences in makeup throughout.17 Examples of this include coffee, steel, and air.
Homogenous mixtures can actually be further classified as solutions. Solutions are made of particles the size of a small molecule.17 The example of air would fall under the definition of a solution because of its small gas molecules. Pizza dough would fall under the categorization of a heterogenous mixture. This is because the ingredients of flour, yeast, salt, and water are not dissolved at a molecular level and keep their individual physical properties.
What are the important things to look for when making pizza dough?
Making a pizza dough can look intimidating on the surface. You walk into your favorite pizza parlor, and you see the worker in the back with flour everywhere and throwing dough into the air with no effort. Making it seem that this is something that the average person cannot do at home or in a classroom. It is actually much easier than you might think and following some important techniques and strategies making pizza can be one of the easier and fun things someone could do, and it all comes down to the science and math of it.
Measuring and Leveling Ingredients
Make no mistake, baking is an exact science and estimating how much of an ingredient you add or using improper tools for techniques can result in an inferior final product. Measuring ingredients properly is very important as baking is not as forgiving as cooking can be; even the slightest miscalculation can turn a soft dough into one that is as hard as a rock. But using a technique called “spoon and level” can be a tool for success.[18]
Flour is one of the most important ingredients in pizza dough and is often the most common to be improperly measured. A measuring cup is the tool of choice when measuring flour, and while your first instinct would be to scoop the flour right out of the bag into the cup, this is the mistake that most people make. Because this packs the flour down into the cup and could end up giving you much more flour than you need. Instead, using a spoon, scoop the flour into the measuring cup until you reach the desired amount. Do not pack or tap the measuring cup as this will cause the flour to settle and give you an inaccurate measurement.18 Once the measuring cup is full, using the flat back of the spoon, level off the top of the measuring cup to remove any excess flour and to give the most accurate measurement.
The Need to Knead
Once the ingredients are measured and mixed, kneading is the next crucial step in the development of the dough. Kneading is the process of physically manipulating the dough by stretching, folding, and compressing the dough many times.[19] These actions strengthen the gluten network by unfolding the proteins in the flour and encouraging them to form weak bonds between their neighbors. The glutenin molecules also form strong end-to-end bonds with each other, creating the gluten chains.19
As kneading progresses, the dough will gradually get harder to manipulate and will take on a smoother look. But be careful not to over knead the dough as those bonds will begin to break down, and the dough will become sticky and no longer elastic, though this is usually only a problem when not kneading by hand.19 Kneading also adds air to the dough as it will trap pockets of air. The air gets trapped and squeezed as you continue to knead forming small and more numerous pockets, the perfect place for the carbon dioxide from the yeast to settle. The more pockets the finer the texture in the final product.19
Some recipes call for little to no kneading, which usually results in fewer and larger air pockets which can create a coarser texture.19 This lack of kneading also means less gluten development when fermentation starts. But as dough rises, the gluten network will continue to develop, so even doughs that are not kneaded too much can eventually rise and give a tender texture.19 This is why some pizza dough recipes advertise no-knead methods, but since our activity will be more hands-on, students will need to know how to knead for this unit.
Pizza Dough Making Being Difficult Might Be a Stretch
The stretching of pizza dough is the culmination of all the work that has been put into the dough and is usually the most intimidating step for first-time pizza makers but with the right techniques even a child can do it. The first key step is to let the dough get to room temperature if it has been cold fermenting in the fridge. When the dough is cold, the gluten proteins have become tight, which makes stretching the pizza very difficult and will result in it just snapping back to its original shape.[20] Letting the dough come up to room temperature for at least thirty minutes before stretching can ease these proteins and make for much easier stretching.
The next step is to give the work surface you will be stretching the dough on some flour or oil to avoid the dough from sticking. Flour works but too much and the dough can become tough. An oil, such as olive oil, is the better option as it not only keeps the dough from sticking to your work surface but also gets it ready for the cooking surface as well and encourages a golden crispy crust.20
Now that the dough is up to temperature and the work surface is ready, it is time to work the dough with some easy techniques. The first being to press the pizza dough before stretching it by flattening it into a disc. Using the palm of your hands and your fingers press the dough from the center making sure to widen the dough into a large circle about six inches across, the dough should be pliable and should not shrink back when pressed.20 If there is a little bit of shrinking back that is fine but if the dough snaps back or if you make a mistake do not worry. An easy fix of resting the dough for about fifteen minutes should make it pliable again.
Once your circle is made, it is now time to stretch the dough with your stretching partner, gravity. While you may be tempted to toss the dough up in the air to do like they do in the restaurants, which can be impressive, by keeping the dough close using your hands to pull and letting gravity do the rest can result in just as good of stretch. When ready, pick up the dough and hold it with both hands on one edge and let the dough hang down. As you do this, gravity will be doing some of the work as you gently rotate the dough in one direction like turning a steering wheel.20 While doing this slowly pull the dough from hand to hand as the dough hangs down.
Continue doing this until the dough has been stretched to the desired diameter, for our activity about eleven to twelve inches. While stretching you may have noticed some thin sports or holes, don’t worry, they are easy to fix before the cooking process. Simply pinch these areas together by pressing around them to cover those spots. The dough circle may shrink back a little; this is common and the reason while most recipes call for over stretching the dough.20 Following these steps and techniques should result in a pizza parlor quality pizza dough.
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