The Chemistry of Bread

Introduction

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The art of making bread, as well as bread itself can date back to some of the first civilizations the world even knows about.Bread has been used as a form of currency, has provided millions of jobs for hundreds of years, and overall has evolved itself over the span of thousands of years to become a surviving staple, as well as a daily food source for humans living in the world today. Bread by accident, has been linked to my own daily life. Early on in my high school career I got a job at a local, neighborhood bakery. Through high school, I kept that job and really got engaged in the art of making bread, as well as the history that makes bakeries all over the world survive, even though their product should be a lost learned art, due to how old it is. Due to wanting to absorb this unique process, I dove into projects through high school revolving around it. Even though I’m not a avid baker or even necessarily want to own a bakery in the future, it is amazing how far bread has come and how the rich culture of it has survived through numerous generations with not only grace and beauty, but the ability to preserve a way of life, and a almost secret clan of chemical reactions along with it.

 
Composition of ...


  • Grains or flour (Which may include, but not always) - Wheat, oats, barley, millet, corn, rye

  • Milk (CH2OH)  or water (for mixing)

  • Eggs

  • Salt (NaCl)

  • Sugar (C12H22O11)

  • Leavening agent- such as baking powder or baking soda, or most commonly used, yeast.

One of the first steps in making bread after mixing the staple ingredients, is to knead the dough. Kneading is a necessary mechanic for several proteins to settle in layers surrounding starch pockets and give the dough it's’ familiar characteristics. Salt, a majority of the time, is added for not only taste, but for the presence of sodium and chloride ions. Both of these needed components are needed for the joining of protein chains, which in turn, forms a stronger formation of dough. During the rising, or “rest” period for the bread dough, the yeast or leavening agent, eats on the sugars present in the dough, and in turn releases the chemical component of carbon dioxide. It’s the formation of CO2 bubbles that trap into the gluten frenzy that in turn, grow and produce the unique texture of bread. At this very same stage, other important chemical reactions involving natural oxidants of the flour, provide links between the protein chains. They are then broken and remade producing the “stretch” of bread, without actually losing its needed structure.  Baking the dough in a oven to produce bread is the last chemical process, due to the amino acids and sugars causing the end product to be the familiar and popular, golden color of almost all baked goods the world knows.


Main Chemicals, Compounds, Components

Flour: Flour is a powder substance that is made by the grinding of either seeds, beans, or a variety of grains. Wheat flour is one of the most important and common ingredients for the modern world. It is a defining and popular ingredient in many countries and cultures, including North America, Europe, the Middle East, India and many parts of North Africa.

Flour was discovered in 6000 BC and the Romans were the first to ever grind wheat seeds in a man-made, original mill. The Industrial Revolution was when flour and mills began to flourish and boom for the world population and the rest of the world. In 1879, the first ever steam-engine mill made its debut in London, and ended up turning the tide for more refined processes of milling flour and the production of bread. Fast forward to the 1930’s and this where flour began to get experimented on. Flour started to be enriched fully, in the 1940’s and the add- ons included niacin, iron, thiamine and riboflavin. It wasn’t until the 1990’s that folic acid was added to that list. Roller mills and Unifine mills have now replaced stone and steam engine mills which has produced more productivity and less labor-intensive work.

There are many different types of flour. These main types of flour include:

  • Unbleached Flour = which is just a simple flour that has not undergone the bleaching process and therefore does not have the white color in it.

  • Bleached Flour or “white flour” = uses bleaching agents which include:

                 -Potassium bromate =which strengthens gluten growth

                 - Benzoyl Peroxide = which is the major part of the bleaching process

                 - Ascorbic Acid = which strengthens gluten development

                 - Chlorine gas = which is a bleaching and maturing agent; it also very well oxidizes starches in the flour, increasing absorption

  • Plain Flour or all- purpose flour = The high in gluten protein found in other bread flours compared to all- purpose flour is 12.5-14.1% to 10-12%. Increased protein is very important because it binds to the flour to capture the carbon dioxide released by the yeast  or leavening agent, which then results in a stronger rise.

  • Self- rising Flour = used to produce lighter and softer products

  • Enriched Flour = when the nutrients that may get lost during the milling processes are put back into the flour   


Yeast: (Saccharomyces cerevisiae)   Yeasts are eukaryotic microorganisms and there are 1,500 known species at the moment. They’re unicellular, but can become multicellular. Yeasts reproduce asexually by the mitosis process and in fermentation, one of the species called Saccharomyces cerevisiae (the most common yeast) converts carbohydrates to carbon dioxide. This is a method that is important in baking.

Yeast is one of the earliest found organisms in history. Researchers have found stones, baking storages and 4,000 + old drawing of bakeries in Egyptian ruins.. Yeast wasn’t always thought to be living organisms, but instead, globular structures. In 1680, Anton van Leeuwenhoek was the first to ever observe yeast microscopically. Even Anton didn’t believe they were live. It wasn’t until 1857, that Louis Pasteur proved in a science supported paper, that the fermentation of alcohol was produced by living yeasts and not just bio - made catalysts.  Now called the “Pasteur effect”, Pasteur proved that by bubbling oxygen in the yeast substance, cell growth would be increased, and the fermentation decreased, resulting in showing that the yeasts were indeed alive.

Yeast in modern day are commonly grown in a lab, and are used in many different productions, which include:

  • to generate electricity in microbial fuel cells

  • the fermentation process of making alcohol/baking baked goods

  • to produce ethanol for the bio-fuel industry

  • as well as many nutritional supplements




Like said before, one of the most common yeasts is Saccharomyces cerevisiae and is used as a leavening agent in baking. The yeast’s main job is to feast on the sugars present in the dough, turning it into carbon dioxide. This is where the dough rises, forming gas bubbles, that after a few minutes, are ultimately ready to be placed in a oven. After the bread is officially taken out of the oven and baked, the yeast molecules die off and the air bubbles or “pockets” are set in place, giving the familiar texture of bread- soft and spongy. In today’s times, one of the most popular retailer of baker’s yeast is called Fleischmann’s Yeast, which was originally founded in 1868. This new, active, dry yeast proved to have a longer shelf life, helped make it rise twice as fast, and required no refrigeration on preservation. In summary, yeast (in making bread) is mixed with flour, warm water or milk and salt. The dough is kneaded until smooth, the yeast respires aerobically, producing carbon dioxide, oxygen decreases and the process of fermentation begins, resulting in ethanol as a waste product. The dough then doubles in size and is put in the oven, baked and after getting out of the oven, is ready to be cooled, sliced and eaten.

Chemistry's Role



Flour: Flour was originally made by man. The seeds, grains or beans were and are, all naturally- occurring ingredients. Through the years though, flour has evolved and is now made at mills in various areas of the world, and is able to be bought in almost every grocery store a person could go to. Flours used for cakes or more delicate pastries use soft wheat. All-purpose flour is made from both soft and hard wheat. Wheat (the most popular form of flour) is first grown in a field and then sent to a flour mill, where it is then stored in silos until needed for milling. Wheat, when decided to be used, goes through a multiple step cleaning process to inspect and purify the wheat and screen for any harmful particles needing of removal. The moisture content is then measured and controlled, to allow the outside layer of bran to be removed during grinding. Once all the conditions are met, the wheat is ready to be grinded. Once grinded, the now new flour is ready to be processed. Usually, small amounts of oxidizing, leavening and bleaching agents, as well as salt, are added to the flour after milling. The flour is then tightly packed in cloth bags and ready to be shipped, sold and used.

Yeast: Yeast is a microorganism, (wild yeast) and is found in plants, fruits and grains. Yeast involves a manufacturing process and is highly controlled by types of farming- preparation, seeding, cultivation and harvesting. Yeast is a naturally occurring ingredient, yet most bought yeast is made in yeast manufactures. (Laboratory) Yeast cells are first clarified and sterilized. This prevents bacteria and prevents organisms from becoming too harmful during manufacturing The yeast seeds are then carefully picked with specific characteristics in mind. ( due to being lab pure) The “seed yeast” is then placed in flasks to be allowed to grow. After a series of steps, it is converted to tanks of about 1,000 gallons in volume. The flasks are then refrigerated for the fermentation cultivation. The “stock yeast” is then fed molasses (the commercial sugar source) and large amounts of air. Finally, it is allowed to be harvested. Harvesting of yeast, is done by sending the cells through centrifugal pumps. The result is a liquid, off-white, “creamy yeast”. Repeated steps of processing and a lot of times drying, are performed for different desired types of yeast.Once chemistry does its desired duties, the product is bread. Though bread may vary in types, the makeup of it is man- made and involves a whole lot of chemical reactions that are usually, not even seen by the naked eye. The first reaction is the yeast. The live microorganism is added to flour, salt and then usually warm water or milk. (along with added ingredients for various types of bread) The ingredients all together, begin to form a sticky, soft dough. The dough is then kneaded, and thus launches the yeast to feast on the sugars present in the dough and eventually converts those carbohydrates to the main chemical component in bread- carbon dioxide. (Respiring aerobically) While carbon dioxide is being produced, the oxygen in the dough decreases, and the process of fermentation begins, resulting in ethanol as a waste product. The dough is then left to rise and once doubled in size with multitudes of gas bubbles within it, is ultimately put in the oven to bake. Once the now baked, warm and delicious bread is taken out of the oven to cool, the last remaining yeast molecules die off and the air pockets that form from it, give the bread its soft and spongy texture almost every American knows too well.

Background Research

Bread is made most commonly in a bakery. There are millions of bakeries located all over the world. Different processes involving leavening agents and flours are used for different variations of bread. Soft wheat is used in the production of cakes and pastries, whereas, hard wheat is used in the formation of common, daily made breads. Variations of bread can be found and bought at neighborhood bakeries, (especially popular in France), local and corporate grocery stores, as well as cafes and speciality food stores. The process of making bread is universal and usually involves a type of flour,(or grains) water, eggs, sugar, salt and a leavening agent, such as yeast or baking soda. Kneading, rising of the bread product and then heat for baking in a oven, are the finishing steps to making products of bread.


Resources

https://www.exploratorium.edu/cooking/bread/bread_science.html

Leaveners in bread and the main chemical components of bread that produce texture and softness.

http://en.wikipedia.org/wiki/Bread#Formulation

The composition of bread during the formation processes

http://www.tpt.org/newtons/TeacherGuide.php?id=1285

Additives that are added to bread to produce, decompose and respire.

http://nzic.org.nz/ChemProcesses/food/6D.pdf  

The main chemical processes in the production of bread

http://www.health.gov/dietaryguidelines/dga2010/DietaryGuidelines2010.pdf

Government guidelines for bread

Information about the grains involved with bread as well as the vitamins in bread itself   

.https://nbclearn.com/files/nbcarchives/site/pdf/52355.pdf

Step by step directions to make bread

http://www.aquimicadascoisas.org/en/?episodio=the-chemistry-of-bread

The importance of carbon dioxide as a chemical reaction of the formation of bread

http://en.wikipedia.org/wiki/Flour

The composition, history, and definitions of flour

http://en.wikipedia.org/wiki/Yeast

The composition, history and definitions of yeast

http://www.madehow.com/Volume-3/Flour.html

Background research and history of flour (Flour mill information)

http://www.madehow.com/Volume-2/Bread.html

Background research and history of bread

http://redstaryeast.com/science-yeast/manufacturing-yeast/

The real importance and reasons to provide yeast in the production of bread


About the Author
Katie Browne is a senior at Billings Senior High School. She enjoys running with her dog Zeus, biking, hiking, camping and ultimately most things performed outside. She has a 3.8 overall GPA average and is in Key Club, Senior Advocates, a runner for Senior High School’s Cross- Country team, a Academic All-State participant, as well as an involved member in National Honors Society. Katie will further her education at the University of Montana in the fall of 2015, to major in Pre- Radiologic Technology.
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