How are bubbles formed and how do they make dough rise in bread?

So we took in biology that carbohydrate is broken into $ce{CO2}$ and ethanol. But all I see in my mind here is that since gas is inside the dough then the gases will try to get out expanding the dough and rising it and I know that ethanol will rise as it is baked. However I am not sure how and why are bubbles formed in the first place or how they're related to this at all and does the ethanol taste stay in bread or is it completely removed once rised?

I heard on another resource that; "It is because air bubbles get stuck inside, and when the bread bakes, the holes appear."

How does bubble getting stuck inside lead to holes appearing? it is confusing me.

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These bubbles have been incorporated into the food using various techniques including simple whipping, mixing, shaking and frying, or more complicated technologies of pressure beating, gas injection, steam generation, extrusion, puffing, thermal expansion, vacuum expansion, dry heating and fermentation, or via the use of rising agents.

Bubbles in food are functional and may be considered an “ingredient”, since they lend a distinctive quality of texture, appeal and luxury, depending on gas content and bubble distribution.

Not only do they have to be cleverly incorporated and balanced during processing, they also need to be stabilised in the food’s final incarnation, so they can withstand transportation and serving.

Achieving stability

When it comes to bread loaves, the gas bubbles within are well-interconnected they have a continuous gas phase within a porous network.

But with many other aerated food products, the challenge is one of stabilisation for this, we assess aerated products according to the duration of time in which their bubbles should appear stable. These bubble stabilisation timescales range from seconds, to minutes, to hours, days, months and years.

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Bubbles are an integral part of many aerated foods, including bread. PHOTO: THE STAR

We expect the tiny bubbles in Champagne to appear soon after pouring, just nice for the bubbles to rise from the bottom of the glass to the surface, to provide a tingling sensation as we sip.

The foamy structure of the creaminess of a milky coffees, or a fluffy meringue should be preserved from between minutes to hours.

The gas bubbles in an aerated chocolate bar should stay isolated as needed, since they provide that sensational melting effect in the mouth which a conventional, non-aerated chocolate bar doesn’t have.

In the manufacturing of aerated food, this stabilisation is aided by ingredients known as stabilisers, mostly emulsifiers.

In bread-making, the emulsifiers used are known as as dough conditioners, e.g. the diacetyl tartaric acid esters of mono- and diglycerides (DATEM, E472e) which help to strengthen doughs, and the distilled monoglycerides (DMG, E471) which act as dough softeners, while sodium stearoyl-2-lactylate (SSL, E481) has a bit of both functions.

The two emulsifiers that frequently show up on ice cream ingredients lists are the mono- and di-glycerides of fatty acids (MDG, E471), and Polysorbate 80 (Tween 80, E433).

Most food aeration processes use air or carbon dioxide, although specific applications do use other gases like nitrogen, argon and nitrous oxide. Nitrogen is also used as a blanketing gas in food processing, to slow down food spoilage due to oxidation.

A bubbly example: bread-making

Bread-making is a perfect illustrative tool for the aeration process, since it occurs in mixing, and in the expansion of volume during the proofing of the dough. Finally, the aerated structure is retained via baking.

During the (manual or mechanical) kneading process, a nuclei of gas bubbles up to eight per cent is incorporated into the dough. Any subsequent folding, punching, rolling, moulding and twisting that the dough may undergo won’t introduce any new bubbles, but will increase the number of bubbles by sub-dividing those already present in the dough – this is called “bubble break-ups”.

Kneading bread. PHOTO: THE STAR / ANN

Gas bubbles are also believed to be trapped within the dry flour particles, as they are added during mixing. These bubbles enlarge during the proofing of the dough, as fermentation takes place.

The carbon dioxide gas produced by yeast diffuses from one point to another according to the concentration gradient – moving from bubbles with a higher CO2 concentration or partial pressure to a bubble with a lower CO2 concentration or with a lower pressure.

The phenomenon by which smaller bubbles disappear and larger bubbles remain or continue to enlarge within the semi-homogenous viscous dough is known as disproportionation.

When two gas bubbles continue to expand up to a size large enough to merge and become one bubble, that’s called coalescence.

The coalescence of gas cells involves the rupture of the dough film between them, which results in the loss of gas and an irregular crumb structure. The complexity of these bubble dynamics eventually stabilises, as the foam structure of a fully-proofed dough with a void fraction of up to 80 per cent is sent to the oven for baking.

During baking, oven temperature will rise to about 180 deg.C. Starch gelatinisation (which begins at about 55 deg.C) and the coagulation of gluten protein (which completes at about 80 deg.C) has the dough setting into a sponge structure. The baked loaf will have a rigid shape, and can contain up to 85 per cent air.

The baked loaf will have a rigid shape, and can contain up to 85 per cent air. PHOTO: THE STAR / BLOOMBERG

Why bubbles matter

Objectively, aeration is all about increasing volume with no nutritional input. This helps in converting hard, tough, even gruel-like food into a lighter, more palatable form, which is more digestible.

It is also more appealing, from both sensory and aesthetic angles.

Texturally, aeration provides a sense of smoothness and luxury to ice creams, lightness to puffs, crispness to biscuits and fizziness to carbonated drinks. It also helps to reduce the intensity of flavours and enhance the perception of them, to trap aroma compounds and then release them for olfactory enjoyment.

Aeration may also alter perceptions of satiety, the feeling of fullness before food is eaten, when it is just viewed.

A group of scientists from the AZTI-Tecnalia Food Research Institute in Spain have worked closely with culinologists to design highly aerated products. They found that consumers experienced a higher level of satiety when presented with a highly-aerated product.

As Malaysian palates progress beyond hunger and even nutrition, that sense of luxury from aerated foods comes more sharply into the picture.

Scientific interchange

A group of 15 researchers from Malaysia braved the cold British winter in January this year, to attend a workshop on innovations in aerated food processing, along with 14 other researchers from Britain, under the Newton Ungku Omar Fund Researcher Links initiative.

I led the Malaysian team, which also comprised two mentors, 10 young lecturers representing local public and private universities, a researcher from the Malaysian Agricultural Research and Development Institute (Mardi), and another from the Malaysian food industry. Prof Grant Campbell from the University of Huddersfield, a world-renowned expert in food aeration, led the British team, who acted as mentors for our team.

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A croissant is built by pockets of air bubbles using the lamination method a perfect one can have 81 flaky, buttery layers of heavenly pastry. PHOTO: THE STAR / 123RF

The workshop was hosted by Campden-BRI, a famous food and drink research institute in the beautiful village of Chipping Campden, Gloucestershire the institute supports the food and drink industries both in the UK and worldwide.

The workshop provided an excellent scientific platform for researchers to meet, share, learn, exchange ideas and discuss problems related to the creation of innovative food products using technologically advanced aerated food processing methods.

The researchers came from diverse backgrounds – there were food scientists, technologists, engineers, chefs, culinologists and industrialists.

Four keynote lectures covered everything from the fundamental principles of bubble creation in foods to innovative processing, structural measurement and the development of novel aerated foods.

Aimed at empowering the Malaysian food process engineering community to translate aerated food opportunities into businesses and markets, the workshop also strengthened scientific interchange and development between participants.

Participants also presented their own work on issues related to baked products, processing, ingredients, development, integration and enhancement.

Focus areas included bread production using other flours, such as rice and sweet potato, as alternatives to reduce our dependency on imported wheat flour, and the production of bread with an altered structure and texture by the modification of air-space mixing, to allow more widespread availability of affordable, high quality and healthy products.

Networking sessions helped to synthesise ideas and project plans including research collaborations and the possibility of running the Bubbles in Food 3 Conference in 2019.

A practical baking session was held in Campden BRI’s training laboratory, led by Dr Gary Tucker, head of baking and cereal processing.

Participants were able to knead and make bread by hand, then try using mechanical mixers under different conditions and formulations – which illustrated the complexity of the bread-making process with regards to mixer type, time and temperature as well as flour type, water levels, and functional and health-giving ingredients.

Baked products were subsequently evaluated (with much explanation) by Campbell and Tucker.


The Chorleywood Bread Process, which helped the UK to utilise its local wheat varieties, was much discussed at this point. Introduced in the 1960s, the process is known for its energy-intensive mixing, using the air-tight Tweedy mixer. This has an integrated pressure-vacuum system capable of reducing up to 85 per cent of the mixing duration of conventional mixers.

The Chorleywood process has helped Britain to utilise its local wheat varieties to make bread with improved volume and whiter crumbs. PHOTO: THE STAR

High pressure air is injected into the mixing chamber in the initial dough mixing process towards the end, the vacuum is drawn very rapidly to make breads with improved volume and whiter crumbs, using local wheat varieties with moderate protein contents. The method and application has spread to other countries like Australia, Africa etc.

Bread engineering

It became very clear that bread-making – the aerated food process which is most well-studied – requires the widest field of knowledge for mastery, encompassing food science, technology and engineering. This spans everything from agricultural engineering for the growth and harvesting of wheat, to the mechanical engineering of mixers and energy efficiency of ovens, to chemical engineering for rates of heat transfer and bubble dynamics during mixing, proofing and baking.

Food engineering consolidates all these aspects and makes it relevant in industrial and manufacturing contexts. Bread-making requires so much science, the physics of bubbles, the chemistry of reactions, the biology of yeast and enzymes – and that’s not forgetting its still unexplained effects and behaviours, which are very much a part of the art of baking.

The workshop ended with a factory visit for the Malaysian delegates to Fine Lady Bakeries in Banbury, where we witnessed UK bread production lines, manufacturing and food traceability processes.

Ideas for tomorrow

After this fascinating, stimulating exchange project, we came home brimming with knowledge, ideas – and the enthusiasm to embark on new aerated food projects. These include the utilisation of composite flour from local resources such as sweet potatoes, by Mardi, and use of seaweed by Universiti Malaysia Sabah.

In Universiti Putra Malaysia, novel technology using the power ultrasound technique was found to have improved aeration in bakery products and have the potential to reduce the usage of emulsifiers.

Other projects involve the substitution of eggs, sugar or fats in baking recipes. Gearing towards the promotion of clean label food products for health promotion, this has also encouraged the growth of the niche artisanal breads and ice creams markets lately, with producers better able to manoeuvre ingredients and processes within a smaller scale production.

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The Science of Bread Baking

Let's do this edible experiment together and see what kids can learn at each step.


  • 1/3 package active dry yeast
  • 3/4 cup warm water
  • 1 tablespoon sugar
  • 2 1/4 cup all purpose flour
  • 1/3 tablespoon salt
  • 2/3 tablespoon cooking oil (e.g. canola oil) or butter



  1. In a large bowl, dissolve yeast and sugar in warm water.
  2. Learn how to measure.
  3. what is yeast? Yeast is a live, single-celled fungus. Active dry yeast is lies dormant (despite the name) until it comes into contact with warm water.
  4. Stir gently and put aside for 15 mins or until you will see a layer of foam form on the surface.
  5. Once reactivated in warm water, yeast begins feeding on the sugars and releasing carbon dioxide. The carbon dioxide forms a layer of small bubbles on the water surface. This is called anaerobic fermentation.
  6. Observe the bubbles.
  7. Add salt, oil 2 cups of flour.
  8. Beat until smooth.
  9. Then stir in enough remaining flour, a little bit at a time, to form a soft dough.
  10. Turn onto a floured surface. Knead until smooth and elastic, about 8-10 minutes.
  11. Kneading mangles and knots together proteins inside the flour to form strands of gluten.
  12. Place in a greased bowl, turning once to grease the top.
  13. Cover with a wet towel and let it rise in a warm place until doubled, about 30 minutes to 1 hour.
  14. Remember yeast is only active in warm water? Yeast needs a warm and moist environment to ferment.
  15. During fermentation, the released carbon dioxide is trapped by the strands of gluten in the rising bread. This is what causes the bread dough to rise, or expand on the surface, leaving behind air pockets throughout the dough.
  16. Punch dough down. Turn onto a lightly floured surface divide dough into smaller doughs.
  17. Notice when you punch down the dough, its size shrinks. That's because the strands of gluten are still soft and cannot hold in shape to preserve the space inside when they're under pressure.
  18. Punching down removes some of the gas bubbles formed during rising and produces a finer grain. It also redistributes the yeast cells, sugar and moisture so they can ferment and rise the dough during the proofing stage.
  19. Shape each into a loaf, a croissant, a butterfly, an animal, etc. Use your imagination. Use a rolling pin if needed - an opportunity to exercise the creative minds.
  20. Place the shaped loaves on a greased pan. Cover with a wet towel and let it rise again (proofing), for about 30-45 minutes.
  21. Bake at 375° for 30-35 minutes or until golden brown. Check occasionally to prevent burning.
  22. Move the loaves from the pan to wire racks to cool.
  23. Study the size of the bread loaves.


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Not only was it fun, but the experiment was also tasty. My daughter refused to share her two big pieces of bread, which was a very good indication that the baking was a success.

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Warning is hereby given that not all activities are appropriate for all individuals or in all situations. Implementation should be undertaken only in appropriate settings and with appropriate parental or adult supervision.

Reading and following the safety precautions of all materials used in an activity is the sole responsibility of each individual. For further information, consult your state's Science Safety Handbook.

Potato Gnocchi Recipe

By David Joachim and Andrew Schloss
from Fine Cooking #127, pp. 24-25

Before domesticating cattle, pigs, chickens, and other animals, human beings harnessed a much smaller living organism: yeast. Without it, some of our earliest foods and beverages, such as bread, beer, and wine, wouldn’t exist. Here’s a closer look at how yeast works its magic so that you can make better breads, rolls, waffles, and more.

What exactly is yeast?

Yeast is a single-celled microorganism related to mushrooms. About 1,500 species exist, but in the kitchen, we use mostly just one, Saccharomyces cerevisiae (which means “sugar-eating fungi”). Used to make bread rise, it’s available in various forms, which differ mostly by moisture content.

Cake yeast (aka fresh yeast or compressed yeast) is made from a slurry of yeast and water with enough of its moisture removed so that the yeast can be compressed into blocks. Experienced bakers swear by its superior leavening and the nuanced, slightly sweet flavor it gives baked goods. Cake yeast is highly perishable and lasts only about two weeks in the refrigerator.

Active dry yeast was developed by the Fleischmann’s company during World War II so that the U.S. Army could make bread without keeping yeast refrigerated. Partially dehydrated and formed into granules, it contains dormant yeast cells that keep at room temperature for several months. To use active dry yeast, rehydrate it first in warm water (about 105°F) along with a pinch of sugar to feed the yeast. The resulting foam is confirmation that the yeast is still alive.

Instant yeast (aka quick-rise yeast) was first manufactured in the 1970s. It’s a smaller form of dry yeast that rehydrates faster and can be added directly to the dry ingredients without being soaked first. Some types of instant yeast, such as RapidRise yeast and bread machine yeast, dissolve faster than others and may include ascorbic acid or other dough conditioners (ingredients that help to strengthen the gluten or soften the crumb).

How does yeast make bread rise?

As bread dough is mixed and kneaded, millions of air bubbles are trapped and dispersed throughout the dough. Meanwhile, the yeast in the dough metabolizes the starches and sugars in the flour, turning them into alcohol and carbon dioxide gas. This gas inflates the network of air bubbles, causing the bread to rise. During rising, the yeast divides and multiplies, producing more carbon dioxide. As long as there is ample air and food (carbohydrates) in the dough, the yeast will multiply until its activity is stopped by the oven’s heat.

Most homemade bread recipes call for an hour or two of rising. This will produce perfectly fine bread, but if you want more artisanal results, give your dough a long, slow rise by putting it in a cool spot, such as the refrigerator. This allows more time for fermentation, which creates desirable secondary flavors that counterbalance the yeast’s earthiness. Along with the yeast, bacteria are growing in the dough as it rises. The bacteria often include some of the same lactic-acid-producing bacteria that turn milk into yogurt, which gives slow-risen breads a delicious tang.

In most bread recipes, the dough rises twice, once before the loaf is formed, and once after. During the first rise, heat from fermentation builds up in the center of the dough ball, the multiplying yeast gets packed into clusters, and alcohol builds along with the carbon dioxide that is rising the dough. Punching down or stirring a dough at this point before forming it into a loaf refreshes the yeast’s environment, evening out the hot and cold spots in the dough, breaking up overcrowded yeast clusters, and releasing the buildup of alcohol, which would result in off flavors and could create a toxic environment that kills the yeast. With a fresh start, the yeast is better able to aerate the loaf during the second rise, just before baking.

What can go wrong?

When bread doesn’t rise, it can be for one or more of several reasons.

The yeast was dead before you used it. When you open a package of yeast, it should smell earthy and “yeasty.” If it doesn’t, you can test or “proof” the yeast’s liveliness by combining it with some of the warm water from the recipe and a pinch of sugar. If the yeast is active, it will produce a bubbly mass within 10 minutes.

The water used was too cold or too hot. Water below 70°F may not be warm enough to activate the yeast, but rising the dough in a warm room will activate it-it just might take several hours. Water that’s too hot can damage or kill yeast. The damage threshold is 100°F for cake yeast, 120°F for active dry, and 130°F for instant. All yeasts die at 138°F.

Too much salt was added or added too early. Adding salt before the yeast has had a chance to multiply can dehydrate it, starving it of the water it needs to survive.

The dough was not punched down or stirred enough. This allows alcohol to build up and poison the yeast.

Beyond Baking

Yeast is used for more than rising bread. It’s essential for brewing beer and making wine, as well as other food products, such as soy sauce and vinegar. Regardless of what it’s used for, all commercial yeasts are select strains of the same yeast used for bread. Here’s a look at what makes each strain different.

Brewer’s yeast comes in two basic types, top-fermenting and bottom-fermenting. Saccharomyces cerevisiae rises to the top of the brew during fermentation and is used for pale ales, stouts, and other top-fermented ales. Saccharomyces pastorianus settles at the bottom during fermentation and is preferred for lagers and pilsners.

Winemaker’s yeast contains strains of S. cerevisiae selected for their vigorous fermentation and tolerance of the 10% to 14% alcohol in most wine.

Yeast extract is a flavoring made from a salted slurry of S. cerevisiae and water. The salt encourages enzymes in the yeast to break down its own protein into its constituent amino acids. One of these is glutamic acid, which has a deep umami (savory) flavor and accounts for the primary taste of products like Vegemite and Marmite. Nutritional yeast is a mild-tasting strain of S. cerevisiae that’s been deactivated. The yeast is then rinsed, dried, and packaged as yellow flakes or powder. Popular among vegans, nutritional yeast has an umami flavor, is often fortified with vitamins, and is a good source of complete protein because it contains all nine essential amino acids.

How much yeast do you really need?

Yeast has a fruity fragrance and an eggy hint of sulfur that’s pleasant in low concentration, but too much can lend a harsh, mushroomy aroma and unpleasant alcohol aftertaste to finished bread. For the best flavor, use a minimal amount of yeast and a long rising time in fairly low temperatures (below 70°F).

The exact amount of yeast needed to rise bread dough depends on three things:

The type of yeast used. You need about twice as much cake yeast as active dry or instant to rise the same weight of dough.

The temperature of the dough. A higher temperature makes the yeast more active, so you don’t need to use as much yeast in a warm environment. You also don’t need to use as much yeast in a cold environment if you’re doing a long, slow rise the only time you’d need more yeast would be for a quick rise in a cold environment.

The length of rising time. The slower the rise, the less yeast you need. You can control rising times to fit your schedule by varying the amount of yeast and the temperature of the rise. For example, a recipe may call for 2 teaspoons of yeast and 2 hours of rising, but if you’re going to be out for the day, you can reduce the amount of yeast to ½teaspoon, rise the dough in the refrigerator overnight, and finish the bread the next day. The lower temperature and longer rising time will allow the yeast to multiply more gradually and create a more complex flavor.

What Makes Bread Dough Rise?

Thanks to the bread-baking craze spurred by stay-at-home orders this spring, yeast is a hot commodity. Home bakers may know they need yeast to make their bread dough rise, but they may not realize how yeast works. If you're squeamish, be warned: The dirty details of your bread recipe may not be something you want to read while eating.

Yeast is a single-celled organism, and it's an essential part of many foods and drinks, including baked goods and beer. Yeast lives in the air all around us, which means you can grow your own at home using just flour and water. (Yeast that's cultivated this way is called starter, and it's used to make sourdough bread). If you don't have a week to collect yeast from the environment, you can purchase the instant yeast or active dry yeast that comes in a packet. This yeast is dormant and can be activated by adding it to warm water.

Yeast alone isn't enough to make bread dough rise, though. To work its magic, it needs two additional ingredients: sugar and time. Yeast cells eat sugar, which is present in flour in the forms of sucrose, fructose, glucose, and maltose. As the microorganisms consume these sugars, they release carbon dioxide gas and ethyl alcohol through a process called fermentation. This is also why adding table sugar or honey to a bowl of yeast and warm water can help activate yeast that's slow to wake up. So when you see a bowl of yeast, warm water, and honey start to foam, you're basically watching yeast fart.

In dough, the carbon dioxide forms bubbles that allow it to rise. It's how a ball of bread dough containing yeast can double in size in just a few hours. The alcohol from yeast also contributes to bread's rise in the oven. In extremely hot temperatures, the liquid alcohol evaporates, resulting in gas bubbles that give the bread some extra height.

Yeast is a common ingredient, which makes it a great entry point into learning more about culinary science. If you want to further your yeast education, this genetic engineering kit lets you make your own fluorescent yeast at home using jellyfish genes.

This bubble bread dough is easy enough to make, but it does take a little patience. Both the dough and the dough balls will need time to rise. To get started, get out a stand mixer with the dough hook attachment. Whisk the yeast and warm water in the bowl of the mixer. Let that sit for about five minutes.

Next, add the sugar, shortening, egg, and 1/2 teaspoon of salt to the bowl. Then, turn the mixer on low and add 1 cup of flour at a time. Finally, use the dough hook attachment to mix on low for 5-6 minutes. If you don’t have a dough hook attachment, knead the dough by hand until smooth. Place the dough in a greased bowl, flipping it over to get both sides greased, and cover it with plastic wrap or a clean towel. Let it rise for about an hour (or until doubled in size).

Aside from alcoholic fermentation, the dough also matures using Lactic Acid Bacteria (LAB). This uses maltose to produces various acids, largely comprising of lactic and acetic acids. Others are categorised as “various organic acids”.

  • Hold shape
  • Stretch (extensibility)
  • Retain gas
  • Produce gas
  • Keep fresh for long
  • Deep flavours and aromas
  • Lower Ph value

During dough fermentation, organic acids in the dough increase. Providing other variables are constant, the longer a dough undergoes fermentation, the more organic acids will exist.

Organic acids are essential to making bread, without them bread wouldn’t be nice to eat.

They help in the production of the bread as it’s machinability improves, has a bigger rise, a bigger oven spring, lighter crumb, tastes, smells and looks more interesting and keeps fresh for longer. All quite important.

Lactic acids

Lactic acid is the key feature of a sourdough starter, but is also found in yeast-made breads. It has the highest concentration of the acids found in bread.

Lactic acid lowers the ph value of the dough and offers many benefits:

Acetic acids

This acid is the key component of malt vinegar. It is also found in sourdough breads in lower concentrations. Here is how it benefits the dough:

Various organic acids

Organic acids also mature the dough and to build a bread with improved qualities.

  • It supports the structure of the gluten
  • Slows down the activity of the yeast
  • Enhances flavour

Though bread can be made without it, we should add salt for great looking and tasting bread.

Active Dry Vs. Instant Yeast

The two most commonly available types of dry yeast are Active Dry and Rapid Rise or Instant Yeast.

Active Dry yeast comes in fairly large granules and generally needs to be dissolved in warm liquid before using.

Rapid Rise/instant yeast is processed into finer particles and was developed to be added along with all the other ingredients&ndashno dissolving required.

In recipes calling for fresh yeast, I usually use 1/3 the amount of dry yeast.

So, if a recipe calls for 1 oz. fresh yeast, I&rsquoll use 1/3 oz (about 9-10 gram) of dry yeast.

PRO TIP: To substitute dry or instant yeast for fresh yeast, use 1/3 the amount by weight. So for 1 oz fresh yeast, use 1/3 oz dry/instant yeast.

8 Secrets For a Moist & Juicy Roast Turkey

Yeast is the driving force behind fermentation, the magical process that allows a dense mass of dough to become a well-risen loaf of bread. And yet yeast is nothing more than a single-celled fungus. How does it do it?

Yeast works by consuming sugar and excreting carbon dioxide and alcohol as byproducts. In bread making, yeast has three major roles. Most of us are familiar with yeast’s leavening ability. But you may not be aware that fermentation helps to strengthen and develop gluten in dough and also contributes to incredible flavors in bread.

Yeast makes dough rise

The essentials of any bread dough are flour, water, and of course yeast. As soon as these ingredients are stirred together, enzymes in the yeast and the flour cause large starch molecules to break down into simple sugars. The yeast metabolizes these simple sugars and exudes a liquid that releases carbon dioxide and ethyl alcohol into existing air bubbles in the dough.

If the dough has a strong and elastic gluten network, the carbon dioxide is held within the bubble and will begin to inflate it, just like someone blowing up bubblegum. As more and more tiny air cells fill with carbon dioxide, the dough rises and we’re on the way to leavened bread.

Yeast cells thrive on simple sugars. As the sugars are metabolized, carbon dioxide and alcohol are released into the bread dough, making it rise.Scott Phillips.

Yeast strengthens bread dough

When you stir together flour and water, two proteins in the flour—glutenin and gliadin—grab water and each other to form a bubblegum-like, elastic mass of molecules that we call gluten. In bread making, we want to develop as much gluten as we can because it strengthens the dough and holds in gases that will make the bread rise.

Once flour and water are mixed together, any further working of the dough encourages more gluten to form. Manipulating the dough in any way allows more proteins and water to find each other and link together. If you’ve ever made homemade pasta, you know that each time you roll the dough through the machine, the dough becomes more elastic in other words, more gluten is developed. And with puff pastry dough, every time you fold, turn, and roll the dough, it becomes more elastic.

Yeast, like kneading, helps develop the gluten network. With every burst of carbon dioxide that the yeast releases into an air bubble, protein and water molecules move about and have another chance to connect and form more gluten. In this way, a dough’s rising is an almost molecule-by-molecule kneading. Next time you punch down bread dough after its first rise, notice how smooth and strong the gluten has become, in part from the rise.

At this stage, most bakers stretch and tuck the dough into a round to give it a smooth, tight top that will trap the gases produced by fermentation. Then they let this very springy dough stand for 10 to 15 minutes. This lets the gluten bonds relax a little and makes the final shaping of the dough easier. This rounding and resting step isn’t included in many home baking recipes, but it’s a good thing to do.

Fermentation generates flavor in bread

As Harold McGee, the author of On Food & Cooking, has pointed out, big molecules in proteins, starches, and fats don’t have much flavor, but when they break down into their building blocks—proteins into amino acids, starches into sugars, or fats into free fatty acids—they all have marvelous flavors. Fermentation, whether it’s acting on fruit juices to make wine or on flour to make bread, does exactly that—it breaks down large molecules into smaller, flavorful ones.

At the beginning of fermentation, enzymes in the yeast start breaking down starch into more flavorful sugars. The yeast uses these sugars, as well as sugars already present in the dough, and produces not only carbon dioxide and alcohol but also a host of flavorful byproducts such as organic acids and amino acids. A multitude of enzymes encourages all kinds of reactions that break big chains of molecules into smaller ones—amylose and maltose into glucose, proteins into amino acids.

As fermentation proceeds, the dough becomes more acidic. This is due in part to rising levels of carbon dioxide, but there are also more flavorful organic acids like acetic acid (vinegar) and lactic acid being formed from the alcohol in the dough. (This is similar to what happens to a bottle of wine that has been left uncorked for a while: the alcohol combines with oxygen to make vinegar.) The acidity of the dough causes more molecules to break down. The dough becomes a veritable ferment of reactions. Eventually, the amount of alcohol formed starts to inhibit the yeast’s activity.

Yeast has help in producing flavorful compounds. Bacteria are important flavor builders as well. There are bacteria in the dough from the beginning, but as long as the yeast is very active, it consumes sugars as quickly as they’re produced, leaving no food for the bacteria, which also like sugar. But when bakers chill a dough and slow down its rise, the cold dramatically reduces yeast activity. The bacteria, on the other hand, function well even in cold temperatures, so they now have an opportunity to thrive, producing many more marvelously flavorful acids.

This loaf of artisan bread owes its complex flavor to a lengthy fermentation, which breaks down big molecules into smaller flavorful ones.Judi Rutz.

The Scientific Secret of Stretchy Dough

Do you remember the last time you baked cookies, bread or cake? Did your baked good turn out perfectly? Or was it a bit too flat or perhaps rubbery and tough, or maybe with clumps of dry ingredients? The problem might have been in how you mixed the dough&mdashor with the type of flour you used. In this science activity you will knead, stretch and punch some pretty remarkable doughs and discover what provides structure and elasticity to your baked goods. Next time you prepare dough for bread, pizza, cookies, cake, pie or any other baked good, you'll know what to do!

Wheat flours mainly consist of carbohydrates and protein, with some fiber. They are classified according to their gluten (or protein) content for a good reason. Getting the right portion of gluten (the protein that naturally occurs in wheat) is essential to getting the right texture in your baked goods. Wonder why? From the moment you bring a liquid ingredient (such as milk or water) in contact with wheat flour, the individual gluten proteins in the flour unravel and hook onto one another, creating strong bonds. With time, an elaborate network of interconnected gluten strings forms. This network holds the dough together, giving it its structure.

Kneading the dough slowly unfolds the entangled network and aligns the long gluten strings in a stretchy, layered web. A pinch of salt helps as well because it neutralizes electrically charged parts of the gluten, allowing them to better slide along one another. The result is an elastic, stretchable dough that traps gas bubbles. Sometimes a dough can be stretched so thin it becomes translucent, making the network of gluten visible with a magnifying glass or microscope. It is the absence of this intricate gluten network that makes gluten-free baking a challenge.

Ready to test and measure your strength against some incredibly stretchy dough? Once you've explored the dough, you'll be ready to bake up a perfect treat!

  • Vital wheat gluten (This is available in well-stocked grocery stores or health food stores.)
  • Wheat flour (Bread flour is preferable, but any wheat flour is fine.)
  • Gluten-free flour (This could be rice flour, corn flour, a gluten-free baking flour mix, etcetera.)
  • Salt
  • Half-cup dry measuring cup
  • Mixing bowl
  • Tablespoon measuring spoon
  • Spoon
  • Water
  • Clean work space


  • Choose a work space that is easy to clean and can take some water spills.
  • Get all of your ingredients out and ready to use.
  • Combine a pinch of salt with one half cup of vital wheat gluten in your mixing bowl. Add three tablespoons of water and mix, first with the spoon, then with your hands. Add one or two more tablespoons of water, if needed, until the flour sticks together and forms a nice soft ball. It should have the consistency of play dough. Place the ball on a clean spot on your work space.
  • Clean your mixing bowl and measuring utensils then repeat the previous step with one half cup of wheat flour and then again with one half cup of gluten-free flour. How do the different flours feel? Does one stick together better than the other?
  • Knead your gluten dough for three minutes. To knead, start by flattening the ball of dough a little. Then fold the dough over itself and flatten as you end the fold. Give the dough a quarter turn and repeat the folding, flattening and turning.
  • Repeat the previous step with the wheat flour dough and the gluten-free dough. Are some doughs easier to knead than others? You might notice that some doughs fall apart as you try to knead them. If so, just take note and skip kneading that dough.
  • Let your dough balls rest for one half hour.
  • While you wait, look at the nutritional content label of the flours printed on the packages. Which one has more carbohydrates per one quarter-cup serving, and which one has more protein?
  • In a moment you will test how elastic the doughs are and how easily they can be stretched.
  • Elasticity measures how well a material recovers its original form after a deformation. Which dough do you expect to be elastic, meaning it bounces back after you punch it? Which dough do you expect to be starchiest? Do you expect you will be able to stretch any of the doughs paper-thin?
  • Now that you have given the gluten network in the doughs some time to develop, you can put them to the test. Lightly punch your balls of dough&mdashall three with the same force&mdashto evaluate their elasticity. Do you see signs of elasticity in any of your doughs?Can you rank them from most elastic to least, or nonelastic?
  • A second characteristic is stretchiness. A dough that stretches well can trap gas bubbles, providing well-risen, fluffy baked goods. Take a ball in two hands and stretch it out between your hands. Does it stretch easily or does it break instantly? Do you need to apply force to get it to stretch out or does it stretch readily? Do this with all three doughs.
  • Some pastries require a paper-thin layer of dough. How thin can you stretch out or roll out your doughs? Can you make any of them so thin that you can almost look through them?
  • Looking at your test results, what type of baked good would each dough be good for: cake, cookies, bread, etcetera? Why do you think this is the case?
  • Extra:What would happen if you let the doughs rest for a longer period of time?Would the elasticity or stretchiness increase? Place your doughs in a container or plastic bag and let them rest for a few hours or overnight. This allows the flours to fully absorb the water and the gluten networks to fully develop. Perform your tests again. Do you notice considerable changes?
  • Extra: Place each dough ball in its own bowl, cover each with water and let them soak awhile. Play with each ball pinch and knead it a little and see what happens. Carbohydrates will wash out whereas the gluten network will create an elastic ball. After washing away all the carbohydrates, what do you think will be left in each type of dough? Try it out and see if your prediction was correct.
  • Extra: Yeast is a live, single-celled organism that feeds on carbohydrates and provides gases that make a yeast dough rise. In which dough(s) do you expect yeast to be most active: gluten flour, wheat flour or gluten-free? The activity &ldquoYeast Alive! Watch Yeast Live and Breathe,&rdquo from Scientific American can help you create your test. Feed the yeast with water&ndashflour mixtures, let it sit for awhile and see if your yeast colony flourishes.
  • Extra: Gluten has several functions in a dough. It binds ingredients and provides structure to the dough. It creates elastic doughs that do not need a mold to keep their form. It also helps retain moisture and prolongs the shelf life of the baked goods. Gluten-free dough mixes use xanthan gum, guar gum and/or ground seeds to take over these tasks.Can you bake a gluten-free bead and a wheat bread and compare their performance against these parameters? You can also bake two wheat breads, one with cake flour (low in gluten) and another with bread flour (high in gluten) and compare their performance against these parameters.

Observations and results
Was the gluten dough elastic and stretchable? Did the gluten-free dough fall apart, showing neither elasticity nor stretchiness? This is expected it is the gluten network that holds a dough together and gives it elasticity and the ability to stretch.

Combine gluten and water, and a network of long, unorganized, knotted gluten strings will form. Kneading aligns these strings, creating a dough you might be able to stretch so thin you can almost see through it. The more gluten, the more elastic, stretchy and strong the dough will be. Mixing gluten and water results in a dough that almost feels like rubber. Wheat flour contains 6 to 12 percent gluten, enough to provide a gluten network that holds the carbohydrates together. This dough is elastic and stretchy, but not as strong and tough as the gluten dough. A gluten-free dough, on the other hand, is crumbly it falls apart easily. Bakers add ingredients such as xanthan gum, guar gum and/or ground seeds to keep the baked goods together&mdashbut making a gluten-free version of some fine pastries, fluffy croissants and delicate wheat breads can be challenging!

This activity brought to you in partnership with Science Buddies

Watch the video: Glass And Candle Experiment. Why Does Water Rise? (January 2022).