A long time ago, unleavened bread was more common. Unleavened bread is bread prepared without the using of any rising agents, such as yeast or soda. During the ancient times, bread making involved mixing crushed grains and water, and then baking the mixture under the sun. And then the Egyptians changed the baking world for the better when they incorporated yeast in the dough. Our ancestors have used yeast, long before writing was invented. But it was only around the 1000 B.C. when the first yeast-leavened bread was baked in Egypt. Egyptians allowed a batch of dough to stand. The semi-domesticated yeast cells grew, allowing carbon dioxide (CO2) to form and make the dough rise. The bread leaved by yeast was soft and taste better. Since then, leavened bread became a staple. Although unleavened breads in many forms are still popular today.
But how exactly bread rise? And why your bread is not rising?
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THE SCIENCE OF RISING BREAD
As we already know, the difference of leavened bread and unleavened is the addition of a rising or leavening agent—commonly yeast. Flour comes from wheat or other forms of grains that contain the proteins glutenin and gliadin. When the flour is mixed with water, the two proteins react to form a loose network of gluten. To better picture how gluten looks like, think of it as a net that holds the entire structure of bread.
Without water, gluten does not form, and more of it is formed when more dough is mixed. Furthermore, kneading the dough makes the gluten network stronger. In addition to this, tiny bubbles are incorporated that get trapped in the gluten. After kneading, the dough is allowed to stand and ferment.
During fermentation, the yeast produces enzymes that convert maltose into glucose, a simple sugar. This glucose is what the yeasts use for energy. In return, they produce carbon dioxide, the gas that enlarges air bubbles, making the dough to rise.
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During baking, the gluten proteins denature because of the high temperature. This forms intermolecular and disulfide bond interaction. From here, the starch and protein network tightens and strengthens, and the gas bubbles run out of room to expand. As the gas bubbles try to expand until they burst, pressure increases, transforming the loaf’s structure from a network of separate gas bubbles to an open, porous network.
The starch continues to solidify and gel like shape during the last stages of baking. The starch granules, on the other hand, continue to firm up after baking and chilling, making the bread easier to slice when cool.
MAKING SURE BREAD IS RISING
Wondering why your bread is not rising at all? There are several reasons why.
Gluten
Gluten formation is one of the first reasons why baked products rise properly. We said earlier that gluten acts as a net that holds the bread together. During dough rising, gluten traps the gas bubbles as fermentation progresses. But if the gluten network is weak or not sufficiently developed, the CO2 may just easily escaped, making it unavailable for leavening. But how do you tell the gluten network has developed? A properly kneaded dough should be elastic, holding its shape well, and springs back when poked.
In batters and dough, carbon dioxide is a primary leavening agent. The amount of flour needed in a recipe is related to the amount of flour used. For example, a high-flour (dough) formulation requires more CO2 production for leavening than a high-liquid (batter) one. As a result, the recipe must contain more of the CO2-forming ingredient.
Sugar and salt
In some recipes, a small amount of sugar is helpful. Sugar in significantly large amount (greater than 10% by weight) dehydrates yeast cells by osmotic effect and reduce dough volume. But this is not always the case since only yeast cells are affected by dehydration of sugar. High levels of sugar are more tolerated for baked goods, including cakes, that are leavened chemically (baking soda and baking powder.)
Further reading: Food Science: The Roles of Sugar In Food
Another ingredient that must not be overlooked is salt. In baking, it has several functions aside from enhancing flavor. Another is that it controls fermentation. Like sugar, it has a dehydrating effect to yeast cells. It also competes with other ingredients for water absorption. The presence of salt will result in less water for gluten formation and starch gelatinization. However, without salt, there will be rapid yeast movement and rapid rising. The overproduction of yeast produces a collapsible and porous structure. And overstretching results in gluten strands that break.
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Yeast
Saccharomyces cerevisiae is the most common strain of yeast used as leavening agent. This strain does its job by releasing zymase enzyme, which metabolizes sugars to produce ethanol and CO2.
Like other living microorganisms, yeasts require certain living conditions to be active. If you have dry yeasts that have been kept for years, check if it is active. Dry yeasts (active and instant) have a shelf life of 1 to 2 years. Check the label for the shelf life. Over time, yeasts lose their potency, and their ability to create bubbles in the dough is affected.
It is better to check if the yeast is active to make sure the dough rises. To do this, prepare a glass of lukewarm water and add the yeast. Then wait 10 to 15 minutes for the water bubbles to start and form on the surface. Try adding a teaspoon of sugar. Yeasts love sugar!
If there is no activity, the yeast is likely dead.
Baking soda and baking powder
Because yeasts are living microorganisms, it is sometimes a task making bread rise. With the advent of chemical leavening agents, including baking soda and baking powder, it has become easier to bake at home. One advantage of these over yeasts is that they do not require additional time for rising. However, they are sometimes confusing to use, especially for first time bakers.
If using baking soda alone as a leavening agent, it must be partnered with another ingredient, an acid, to make it work. This ingredient can be a dry acid like cream of tartar or a liquid acid like buttermilk, citrus juice., honey, molasses, and applesauce. Baking soda is an alkaline, and in order to work, it must rely on acid included in the recipe.
The reaction between baking soda and the acid creates CO2, forming bubbles within the dough or batter. To use baking soda, 1/4 teaspoon per 1 cup flour should do the work. Too little baking soda will not make the dough rise appropriately. However, too much baking soda will make the bubbles bigger. These bubbles will only end up joining together. And when they rise to the top, the dough will burst, resulting in a flat product. Furthermore, the excess baking soda will no longer be neutralized by the acid. The result is metallic-tasting and coarse-crumb bread.
Baking powder is no different to baking soda. It contains sodium bicarbonate (baking soda), cornstarch and a dry acid (cream of tartar). The cornstarch is there to prevent premature production of CO2 during storage. Commercial baking powder must include at least 12 percent CO2 gas by weight (per 100 g of baking powder must contain 12 g of CO2), while home-use powders must have 14 percent CO2.
Baking powder starts its work when it becomes wet. This activates the dry acid to come into contact with baking soda, creating CO2. Bakers use baking powder rather than baking soda when the batter lacks natural acidity.
References:
V. Vaclavik, E. Christian (2014). Essentials of Food Science (4th edition). Springer.
M. Wallert, K. Colabroy, B. Kelly, J. Provost (2016). The Science of Cooking: Understanding The Biology And Chemistry Behind Food And Cooking. John Wiley & Sons, Inc..
M. Gibson (2018). Food Science And The Culinary Arts. Academic Press.
G. Crosby, America’s Test Kitchen. (2012). The Science of Good Cooking: Master 50 Simple Concepts to Enjoy a Lifetime of Success in the Kitchen. America’s Test Kitchen
