2. Background
As you can see, bread,
cakes, and cookies all look
very different even though
they are made from almost
the exact same ingredients.
The cause of these
differences is the leavening
process.
Cakes and cookies are
chemically leavened, but
bread is leavened by yeast.
3. Bread Leavening
When people bake bread, they are also making
a chemical reaction.
This chemical reaction, usually involving yeast,
is called alcoholic fermentation.
The yeast ingests the sugar in the bread dough
which breaks down into ethyl alcohol and carbon
dioxide.
The ethyl alcohol and carbon dioxide are the
most important part of the chemical reaction.
4. Bread Leavening
The carbon dioxide
creates air bubbles
which make the “light,
airy texture of bread.”
The carbon dioxide
does not escape the
bread because a gluten
protein in the wheat of
the flour forms a
network of fibers that
blocks the air bubbles
from escaping.
5. Bread LeaveningThe wheat used in
bread dough contains
enzymes that act as
catalysts to the
reaction.
Ethyl alcohol is equally
important as it
contributes to the taste
and smell of the bread.
Organic acids, esters,
and ketones are also
products made during
6. Cake and Cookie LeaveningThe wheat used to make cakes
and cookies does not contain as
much gluten as the wheat used
to make bread.
Because of the lack of gluten, the
carbon dioxide is not easily
trapped inside cakes or cookies,
so an acid-base reaction is used.
In many recipes, baking soda
(sodium bicarbonate) acts as the
base in the reaction, and the acid
can be a variety of ingredients.
The most common acid used is
baking powder, which is actually
a combination of acids that
release carbon dioxide at
7. Cake and Cookie LeaveningCalcium biphosphate is the
acid used in most baking
powders, but sodium
aluminum sulfate may also
be used.
When the acid is dissolved
in water, hydrogen ions are
released and “react with
the bicarbonate ions from
the baking soda”.
This important acid-base
reaction occurs so that the
cake and cookies are light
8. Works Cited
Ashe, Arthur J. , III. "Yeast." World Book Advanced. World Book, 2013. Web. 7 Apr. 2013.
<http://www.worldbookonline.com.candycorn.lipscomb.edu/advanced/article?id=ar613160&st=yeast>
Connick, Wendy. "The science of bread." Countryside & Small Stock Journal Mar.-Apr. 2011: 70+. General OneFile. Web.
7 Apr. 2013. <http://go.galegroup.com.candycorn.lipscomb.edu/ps/retrieve.do?sgHitCountType=None&sort=DA-
SORT&inPS=true&prodId=GPS&userGroupName=tel_a_beaman&tabID=T003&searchId=R1&resultListType=R
ESULT_LIST&contentSegment=&searchType=BasicSearchForm¤tPosition=1&contentSet=GALE%7CA2
49956737&&docId=GALE|A249956737&docType=GALE&role=ITOF>
"Fermentation of Sugar in Bread by Yeast." Kinetics of Cooking. Arizona Board of Regents for The U of Arizona, n.d. Web.
7 Apr. 2013. <http://blowers.chee.arizona.edu/cooking/kinetics/kinetics.html>.
http://blowers.chee.arizona.edu/cooking/kinetics/bread.html
"On the Rise." Chemistry World Oct. 2009: 54-57. RCS. Web. 7 Apr. 2013.
<http://www.rsc.org/images/BreadChemistry_tcm18-163980.pdf>.
Rudolph, Melissa. "Leavening: How Great Cooks Loaf." Chem Matters Apr. 1996: 4-6. Print.
