CHAPTER 13: LEAVENING AGENTS Flashcards
Are baking powders all alike?
No. In fact, they have some interesting and important differences that are often overlooked.
Three main leavening gases in baked goods.
Carbon dioxide, steam, air.
Sometimes, bakers and pastry chefs categorize leavening by what?
The method used to incorporate (forming or adding) leavening gases to batters or doughs.
Three categories of leavening.
Physical, biological, and chemical leavening.
Does leavening often start before baked goods are placed in the oven?
Yes
Are leavened baked goods light and porous?
Yes, they are higher in volume and more tender than if unleavened.
Are leavened baked goods easier to digest?
Yes
Three forms of matter.
Liquid, solid, gas.
When temperature changes, can matter change from one form to another?
Yes, sold ice to liquid, liquid to gas.
What happens to molecules as temperature increases?
They spread out and start moving faster.
Were the very first breads leavened or unleavened? How were they made?
Unleavened, more like flat tortillas made by moistening and baking ground nuts, cereal grains, or seeds.
First civilization to leaven bread. What did they use?
Egyptians as early as 2,300 BC, they used breadmash, which contained wild yeast from the air, to lighten doughs.
For many centuries after the Egyptians started leavening bread, was yeast was the only leavening agent?
Yes
When were chemical leavening agents introduced?
Late 1700s
First popular chemical leavening agent.
Pearl ash, a crude form of potassium carbonate, an alkali.
Pearl ash was removed from what?
The ashes of wood.
What came after pearl ash?
Baking soda, which was used with sour milk or a cultured dairy product.
What is the acid by-product of wine making?
Cream of tartar
Almost a hundred years after baking soda, what became commercially available next?
Cream of tartar, it was used in the first commercial baking powder.
How is baking powder made?
Mixing cream of tartar and baking soda with cornstarch.
Baking soda is also called what?
Sodium bicarbonate
Where was the first baking powder produced?
In San Fransisco, near the winemaking region of CA.
Were baking powders refined throughout the 1800 and 1900s?
Yes, with newer, more versatile acids replacing cream of tartar.
Are there several types of baking powder available today?
Yes
Baker’s yeast was first purified and sold when?
1800s…no longer was the baker at the mercy of the flavor and gassing properties of wild yeast starters.
Few changes were made until the 1940s, when ____ ___ _____ was developed.
active dry yeast
Does active dry yeast perform like fresh yeast?
No, it did not and wasn’t widely used by professional bakers.
When was instant yeast developed?
Late 1970s
What was so great about instant yeast?
It combined the convenience of dry yeast with the performance of fresh.
What expansion is the basis for leavening?
Molecules moving faster and spreading apart as temperatures increase.
What happens at a cellular level when gases expand from heat in the oven?
The force from these expanding gases pushes on wet, flexible cell walls, causing them to stretch. As long as structure builders stretch without excessive breaking, volume increases.
What happens to gases when baked goods are removed from the oven?
Gases evaporate or contract back to their original volume. Products with strong structure retain their shape.
Name to baked goods with weak structures that will shrink in size or collapse once gases evaporate or contract back to their original form.
Souffles and under-baked cakes.
Timing is important. For best volume, when must gas expansion occur? Use yeast-raised doughs as an example.
While baked goods structure is still stretchy and flexible, yet intact. In the case of yeast-raised baked goods, these ideal conditions occur during bulk fermentation, proofing, and the early stages of baking.
What happens to gases in bread doughs made with rye and other flours that do not contain sufficient gluten?
They won’t rise properly because gases from fermentation escape from the dough soon after they are formed.
Do all liquids and gases expand when heated?
Yes
Besides air, steam, and carbon dioxide, name another liquid and gas that can be important in certain baked goods.
Alcohol and ammonia.
What is steam?
Water vapor, or the gaseous form of water.
When does steam form?
When water, milk, eggs, syrups, or any other moisture-containing ingredient is heated.
Is steam a very effective leavening agent? Why?
Yes, because it expands to occupy over 1,600 times more space than water. Imagine the power of this huge increase in volume.
Do all baked goods rely on steam for at least some of their leavening? Why?
Yes, because all baked good contain water or another liquid. In fact, many baked goods rely on steam for leavening more than one might imagine.
Do sponge cakes rely on steam for leavening? Why?
Yes, they rely on it as much as air. That is because SC batters are high in eggs, which are high in water.
Certain baked goods, such as choux pastry and popovers, are leavened almost exclusively by what?
Steam
Steam leavened baked goods are usually cooked in what?
Very hot ovens.
Besides leavening, what other uses does steam have for baked goods?
It’s injected into ovens during the early stages of bread baking. This keeps crusts from forming too early, allowing bread to rise to its fullest potential without constraints of a hardened crust. Steam also affects the quality of bread crust.
How does steam affect the quality of bread crust?
Because crust formation is delayed, the crust remains thin, and there is enough time and moisture from the steam to fully gelatinize starches. Gelatinized starches are needed to form a crisp, glossy crust.
If volume is low in baked good, it could be that leavening was not properly timed with structure formation. What questions should you ask yourself to problem solve?
Is the oven working properly, and is it set to the correct temperature?
Is the product properly formulated, and were ingredients measured accurately?
Is the baking powder too fast- or slow-acting?
Was unbaked batter left out too long before it was baked?
Why is a low oven temp bad for leavening? Why items is this bad for?
It slows the formation and expansion of gases. This is especially bad for steam-leavened baked goods such as choux pastry, puff pastry, and certain sponge cakes.
High amounts of sugar and fats slow what? How does this affect leavening?
The coagulation process of proteins and gelatinization of starches, causing gas to be released before structures are set.
What happens if unbaked batter is left out too long before it is baked?
Small bubbles tend to migrate to large bubbles in thin batters, and large bubbles tend to rise to the surface and escape.
Can temps that are too high affect steam leavened goods? How?
Yes, a hard crust may form too quickly not allowing the baked goods to reach their maximum height.
Why is choux paste hollow when baked?
Raw egg proteins start twisted and coiled. As steam expands, egg proteins uncoil and stretch, and the paste puffs. Steam continues to expand, putting pressure on the stretched egg proteins. Eventually most of the egg protein structure breaks from the pressure, creating a characteristic cavity in the baked choux paste.
Why does the outside of baked choux paste resist breakage?
Gelatinized starch and coagulated egg proteins in these walls harden and set, defining the shell’s final volume and shape.
What happens if choux pastry shells aren’t thoroughly baked?
If side walls are even slightly moist, they will be weak. When the shells are removed from the oven and steam evaporates and condenses back to water, egg proteins in still-wet walls recoil. When this happens, shells shrink and collapse.
How should you check to see if a choux shell is sufficiently baked?
Do no rely on color alone. Remove a single shell to see if the inside is dry. If it is, the whole batch is ready to come out.
An undermixed batter creates what on the volume and crumb structure of baked goods?
Poor volume and coarse texture.
Properly mixed batter creates what on the volume and crumb structure of baked goods?
High volume and fine texture.
Overmixed batter creates what on the volume and crumb structure of baked goods?
Poor volume and dense texture.
Why is it easier to understand the importance of air to angel food cake and sponge cake but harder when comparing other baked goods such as cookies and biscuits?
Both angel and sponge cakes contain egg whites that are whipped and noticeably change in volume; the others don’t.
Without air, would baked goods leaven?
No
How is air added to batters and doughs?
Through physical means: whipping, creaming, sifting, folding, kneading, and even stirring.
Is it near impossible to mix ingredients without adding some air?
Yes
What else do the physical mixing processes do besides add air? Example?
These physical processes also serve to break larger air cells into smaller ones, for a finer, more uniform crumb. Yeast-raised dough that has undergone bulk fermentation is punch down to redistribute gas bubbles into many smaller ones.
Like water, air is present in what?
All baked goods.
Unlike water, air is already a _____.
gas
While it expands a little when heated, air is already a gas and does not expand nearly as much as _______.
water
Air’s role is subtler than water but no less important. Why?
When air is added to batters and doughs, it is added as small air bubbles or air cells during the mixing stage. These air or gas cells present in raw batter or dough can be thought of as seed cells. During baking, steam and carbon dioxide gas move to these seed cells, enlarging them. No matter how much water vaporizes into steam, no matter how much carbon dioxide is produced, no new air cells form during baking. Instead, steam and carbon dioxide fill and enlarge the seed cells that are already present in the batter or dough. Without seed cells, there would be no place for the gases to go except out. Without seed cells, there would be no leavening.
Why is it important to understand what it mens to whip, cream, knead, fold, and sift ingredients?
Batters and doughs will not aerate properly, and crumb appearance and volume will suffer.
If gases that expand during baking move to the few air cells formed during mixing, what happens to the size of air cells if enough aren’t created?
The fewer the air cells, the larger those few will grow. Large air cells in baked goods mean a coarse crumb.
What happens if too many air cells are introduced into baking?
Egg and gluten proteins in the cell walls become overstretched, and cell walls are thin and weak. During baking, these thin cell walls stretch and further collapse. Again, the baked good will have poor volume.
The only one of three main leavening gases that is not present in all batters and doughs.
Carbon dioxide (while present in air, it is present in trace amounts only).
Carbon dioxide forms from what?
Yeast fermentation or chemical leaveners.
What is a biological source of carbon dioxide?
Yeast fermentation
What are chemical sources of carbon dioxide?
Baking soda and baking powder.
Is the role of carbon dioxide in leavening sometimes overstated? Explain.
Yes, many cakes are leavened more by steam and air than by carbon dioxide.
Are yeast cells very small single-celled organisms?
Yes
How many yeast cells are in one pound of compressed yeast?
15 trillion
Fermentation is a process in which yeast cells break down _____ for energy. Yeast uses the energy for what?
sugar; survival and reproduction
How do yeast cells reproduce?
Sugar energy is used for budding. This is where enlarged cells will break off from each other. They even leave scars from previous buddings.
Although yeast breads had been produced for thousands of years, it wasn’t until when that who proved living yeast was necessary for fermentation?
mid-1800s, Louis Pasteur
Yeast can be thought of as what?
Tiny enzyme machines, breaking sugars into smaller and simpler molecules with every step.
What does yeast lack? How does this affect starch?
It lacks amylase and cannot break starch down into sugar. That is why amylase is an important additive in bread baking, especially in lean doughs.
What is a lean dough?
Those consisting of little more than flour, water, sat, and yeast.
Most common means of adding amylase into lean doughs?
Dry malt
Before it was understood that there are many steps in the breakdown of sugars to carbon dioxide, it was thought that an enzyme called what was responsible?
Zymase
The many steps of sugars being broken into carbon dioxide is called what?
Glycolysis, and separate enzymes control each step.
The term zymase is still sometimes used to refer to what?
The many enzymes in yeast that take part in the breakdown of sugars.
Overall process of yeast fermentation.
sugar —(yeast)—-> CO2 + alcohol + energy + flavor molecules
Does fermentation produce as much alcohol as it does carbon dioxide?
Yes
Most bakers would say that most important end product of fermentation is what?
Carbon dioxide, but alcohol adds significantly to oven spring, making it an important leavening gas..
Besides carbon dioxide and alcohol, what else is produced during fermentation? Why are they overlooked?
Small amounts of flavor molecules, including many acids. The molecules are sometimes overlooked because there are too many to name, and each is generated in such small amounts. Yet, they are the distinct aroma of freshly baked yeast bread. Often long, slow fermentation is best for developing the most desirable flavor.
Is the rate of yeast fermentation affected by several factors?
Yes
When is fast fermentation desirable?
When there are time constraints.
Slower fermentation is more desirable for what?
Flavor and gluten strength.
