Yeast is widely used for making bread, beer, and wine. People all over
the world drink and eat those products. Bread is the main product that
people eat out of the three.
Humans need heat to survive. Without heat from the sun we would not
survive. We also need heat for food. If the temperature never changed and
it was always hot or cold we could not grow crops. Most people don’t
live in the Sahara desert or in Antarctica; this is because our bodies
need a steady body temperature. Without a steady body temperature
humans could not live. Anything else that is living also needs a
certain temperature to live. Humans can hunt meat, but without cooking
the food it does not taste as good, or is as safe. You also need cooking
for killing germs. Some water can be very infected with all sorts of germs
but if you boil it then the germs will get killed. Humans also need heat
for manufacturing. Almost everything that humans manufacture uses heat
during the manufacturing process.
Temperature is the relative hotness or coldness of a body or an environment.
It is also
a numerical measure of hotness or coldness on a standard scale such
as Celsius and Fahrenheit.
A thermometer is an instrument that measures, and indicates temperature,
especially one that consists of a glass tube in which a liquid expands
or contracts as the temperature increases or decreases. Humans need thermometers
to measure temperature. If we did not have thermometers to measure temperature
we could burn or freeze our selves.
Thermodynamics are the part of physics that deals with the relationships
between heat and other forms of energy. In thermodynamics there are
two laws. The first law states that energy cannot be created or destroyed.
The second law says that heat or energy only moves from something of higher
heat energy to something of less heat.
Yeast is any of various one-celled fungi that can cause the fermentation
of carbohydrates, producing carbon dioxide and alcohol. Bakers put it in
bread to make it rise. Yeast is also used for the production of beer and
wine. Yeasts that are used commercially consist of masses of microscopic
yeast organism. There are about 600 different types of yeast. Few of the
types are used commercially. Yeast is a type of fungi that is almost everywhere.
It is even in the air. The reproduction of yeast happens very quickly.
Substances that contain sugar are the substances that yeast grows well
on. By splitting in two or budding the yeast reproduces. Part of the cell
wall of the yeast swells then forms a new growth or a bud. The bud turns
into its own independent cell.
The Importance If Yeast
Yeast is important because it is used for making food, which people
eat. Yeast is used in the making of bread, beer, and wine. Bread in particular
is an extremely important part of peoples’ diets worldwide.
How Yeast Is Used
Yeast has a lack of chlorophyll. The lack of chlorophyll in yeast means
that yeast has to rely on other things for food. Fruit, grain, nectar,
and molasses are the things yeast feeds on for sugar. Yeast breaks down
its food by producing a chemical called ferments or enzymes. Some species
of yeast break down their food into alcohol and carbon dioxide. That process
is called fermentation. Fermentation is important in making bread, beer,
The History of Yeast
In the early years people didn’t know much about yeast. In the 1600’s
Anton Van Leeuwenhoek, a Dutch scientist, discovered yeast cells first.
In 1860 Louis Pasteur, a French scientist, confirmed the cause of fermentation
of wine and beer.
People all over the world eat bread. Bread gives people energy and protein.
The staff of life is what bread is often called. To make bread you have
to bake dough that consists of flour or grain meal. The flour or grain
meal is mixed with water or milk. The people in many Western countries
mainly bake loaves or rolls made with wheat flour. People eat crispy and
thin sheets of bread called flat bread in other parts of the world. Flat
bread is made from grains like barley, corn, oats, rice, rye, wheat, or
four made from these grains. Flat bread does not have yeast or other leavening
agents to make it rise. Some people make bread by hand. In commercial bakeries
bread is made by machine.
Kinds of Bread
There are mainly three groups of bread. There is yeast bread, quick
bread, and flat bread. Yeast raises yeast bread. Quick bread has a quicker
preparation before baking. Quick bread rises by baking powder or other
substances that raise dough. Flat bread also takes less time to prepare
before baking. Flat bread uses little or no substance at all to help it
There are other types of breads in the three groups. Yeast bread includes
pan bread, hearth bread, and other breads that are yeast-leavened.
Pan bread is baked in a container. Pan bread includes bread made with white
wheat flour and breads like raisin bread and whole-wheat bread.
Corn bread, doughnuts, muffins, and pancakes are all included in quick
bread. Most quick bread is made at home. Quick bread is also made in local
bakeries and supermarkets.
Flat bread is a main food throughout the world. In Central America people
eat many types of flat breads made from corn or wheat flour, called tortillas.
Flat bread can also be made from rice flour. In India people eat flat bread
called chapatti. Chapatti is made from coarsely ground wheat. Pita
bread is another type of flat bread, is made from durum wheat.
How Yeast Bread is Made
Commercial bakers and home bakers make bread from dough consisting of
at least four ingredients. These ingredients are flour, water or milk,
salt, and yeast. Other ingredients that might also be in the dough are
eggs, shortening, sugar, or other foods. Commercial bakers use enriched
dough for white bread. To enrich the dough, bakers use vitamins and minerals.
Some bakers just use already enriched flour. Dough conditioners and shelf-life
improvers are in most commercial dough. For bread to be able to get
a smooth and even texture bakers use chlorine dioxide and potassium bromate.
Monoglycerides keep bread from getting stale and improved shelf-life. Calcium
propionate reduces the growth of mold and bacteria.
There are two processes for making dough into bread. One is conventional
bread making and the other is continuous bread making. Most bakeries
use the process of conventional bread making. Home bakers also use the
conventional bread making process, but they vary the process. The largest
bakeries use the continuous bread making process.
When using the conventional bread making process the ingredients are
mixed by one of two main methods. One is the sponge-and-dough method the
other being the straight dough method. In the sponge-and-dough method the
ingredients are combined in 2 stages. The first stage mixes up all of the
yeast and some of the flour and water or milk. Once these ingredients are
mixed this mixture is called a sponge. Bakers then let the dough rise for
16 hours at about 85° F. The other ingredients are then added to the
mixture. Then it rises again for a little while. In the straight dough
method all of the ingredients are put in and mixed at once. Then it rises
for 3 hours at 85° F. After both of these processes the dough is cut
into the right shape or size. Then they rise for a little longer. The bakers
cook the dough in an oven at about 450° F.
In continuous bread making people use highly specialized equipment.
They use this equipment when they are mixing the ingredients and preparing
the dough so it will be ready for baking. In the most common methods the
ingredients are all added together expect the flour. This mixture is called
broth. After the mixture rises in a tank the broth is pumped to a mixer
and flour is added. While the ingredients are in the mixer they are put
under pressure and then it forms dough. The dough is then divided and shaped.
Then the dough is sent to the oven so it can be baked. The dough forms
to a bread of uniform shape, texture, and quality. After the baking
of the bread, it is removed from the oven so the bread can cool. When the
bread is made commercially it is put in a cooling machine where there temperature
drops about 100°F. Then the bread is sliced and wrapped.
Yeast is useful and important to humans in many ways. Temperature is
very important to yeast growth. Yeast is used in bread, which is imperative,
because most people eat bread. We could live without bread but it is still
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