Transcript Leavening Agents

Leavening Agents
Chapter 21
Air
• Air is not the main leavening agent ,but
gives many products a “lift”
• Air is the principal leavening agent in
meringues and angel food cakes
• These products are based on egg foams (beaten
egg whites)
• Protein traps the air bubbles in the foam, creating
a light and fluffy texture.
Steam
• All recipes for baked goods include some
liquid.
• The water in the liquid produces steam when
heated
• The temperature of the oven usually at least
204ºC ( what is that in ºF)
• Baking coagulates the protein, setting the
structure
• Making large pockets or whole appear in food
Carbon Dioxide (Co2)
• Two basic methods for creating carbon
dioxide:
– Using baking soda, baking powder to create
a chemical reaction that yields the gas
– Using yeast in a biological process to create
gas
– http://recipes.howstuffworks.com/bread.htm
Baking Soda
• Baking Soda = chemical compound sodium
bicarbonate
• Baking soda releases sodium carbonate as well
as carbon dioxide when heated
• Sodium carbonate gives food a bad taste and a yellowish
color.
• However, baking soda is always used with an acid, which
alters the chemical reaction to prevent sodium carbonate
from forming
– Some examples of acid are buttermilk, vinegar, lemon juice,
molasses, honey, fruits, fruit juices, and cream of tartar.
Baking Powder
•
Baking Powder = leavening compound that contain
baking soda, dry acids and starch or some other filler.
•
•
The filler in baking powder, usually cornstarch or calcium
carbonate, absorbs moisture in the air, which helps prevent a
chemical reaction from taking place too soon.
Baking powder comes in two types:
1.
Single-acting baking powder = as soon as liquid is added,
carbon dioxide starts to be released
–
2.
The quick reaction occurs because the acid in baking powder is
soluble in a cold liquid
Double-acting baking powder = usually preferred, contains two
acids, one that reacts with cold liquid and one that reacts with
heat.
–
Some carbon dioxide is released as soon as liquid is added, but
most is produced as the batter heats in the oven
The Strength of Baking
Powder
• http://chemistry.about.com/cs/foodchemistry/f/blbaking.htm?p=1
• By federal law, baking powder must yield at
least 12%. of carbon dioxide, most home used
are at 14%
– To much baking powder will cause the walls of the
flour mixture to stretch too far, break, and collapse.
– Too little will mean a compact product
– http://images.google.com/imgres?imgurl=http://static.flickr.com/102/307
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Ammonium
Bicarbonate
• Baking soda and baking powder are the
most common chemicals used to produce
carbon dioxide, however ammonium
bicarbonate can be used.
– Ammonium bicarbonate produces carbon
dioxide as it decomposes
– Mostly used in crackers and certain types of
cookies because of the affect to taste
Producing Carbon Dioxide
(CO2) with Yeast
• Yeast is a microscopic organism that
produces carbon dioxide through
fermentation = biological reaction that
slowly splits complex organic compounds
into simpler substances
• During fermentation, yeast converts sugar into
ethyl alcohol and carbon dioxide, ethyl alcohol
evaporates while the carbon dioxide causes the
product to rise
• Yeast is killed in high baking temperatures
The Origins of Yeast
• Thousand of years ago a little yeast landed on
some bread dough and started to ferment,
making the dough rise.
• Ancient Egyptians first leavened bread by using yeast piece
of leftover dough.
– They started getting the same results using beer froth which
also contains yeast
– The word “yeast” originally meant the froth or sediment of a
fermenting liquid
– In ancient Rome, grape juice was mixed with wheat bran,
ferment to develop yeast. The cakes were cut and used for
bread later.
– Sourdough bread is made by keeping the yeast alive from one
batch of bread in order to start the next one.
• http://video.google.com/videoplay?docid=
2261363315131027664&q=yeast&total=1
220&start=10&num=10&so=0&type=searc
h&plindex=9
• Picture of yeast dividing (producing CO2)
Batters and Dough
• Pour batters – made with an equal ratio of flour to
liquid, usually flour (ex. waffle and pancake)
• Steam is the main leavening agent in pour batters
• Drop batters – mixing about two parts flour to one part
liquid
• Make muffins and some cookies, baking powder and steam are
both leavening agents
• Soft dough – three parts flour to one part liquid
• Needs more mixing to develop gluten, example yeast breads, pizza
crust and baking powder biscuits
• Stiff dough – six to eight times as much flour as liquid
• Drier consistency is needed for some products example pie crust
• Steam leavens all flour mixtures
Making Yeast Products
• Beside yeast, the basic ingredients these
breads are flour, liquids, and salt
– Flour – provides the starch as well as the proteins
that produce gluten
– Liquid – usually water or milk. Milk is often chosen
for nutritious reasons and also helps bread stay fresh
longer
– During baking, the steam from the liquid combines with the
carbon dioxide produced by the yeast, which helps the bread
expand and rise
– Sugar, fat, and eggs – sugar helps the crust brown,
fat makes the bread tender (softer), eggs makes the
bread richer in texture and flavor.
Making Quick Breads
• Quick Bread = needs no time to rise.
These products are made with a
leavening agent other than yeast, usually
steam or carbon dioxide that is produce
with baking powder or baking soda. Ex.
muffins, coffee cakes, biscuits etc.
• All quick breads contain flour, liquid and salt, plus
a chemical leavening agent.
• When making quick breads, DO NOT OVERSTIR,
this will develop gluten, producing a tough
product.
Questions
1. What are the three main leavens in bake
goods?
2. How do each of the two natural leavens work?
3. What are two methods for producing carbon
dioxide for leavening?
4. How does baking soda work as a leavening
agent?
5. What would happen if you let out the lemon
juice in a recipe that called for lemon juice and
baking soda?
6. Compare single-acting baking powder with
double-acting baking powder.
Question Continued
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13.
How much baking soda is in a recipe that calls for 2
teaspoons of baking powder. How do you know this?
Why does the amount of baking powder used in a recipe
matter?
Describe how yeast produces carbon dioxide for
leavening.
What is the scientific basis for the ancient Romans’ choice
of grape juice and a grain products for growing yeast?
Should yeast be refrigerated? Why or why not?
Why do batters need to be thin when steam is the main
leavening agent?
Are cakes leavened with only one leavening agent?
Explain