How temperature affects the rate at which bread dough rises and find out the optimum temperature for yeast to work?

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Irfan Enayet

Year 11



) Introduction:

To begin, I will first describe the factors that can affect the rate at which the bread dough rises.

* Amount of sugar: when we add more sugar, the reaction speeds up, as there are more sugar particles in the given space. This causes more collisions to take place therefore the reaction goes faster and the bread dough rises quickly.

* Amount of Yeast: increasing the amount of yeast provides more enzymes for the reaction in other words the active sites are filled up quickly; consequently the reaction is faster.

* Amount of flour: excess flour would slow down the reaction, it means if the quantity of flour is bigger than yeast then the reaction goes slow! This is because the action of the enzyme in yeast is weakened; the reaction slows down.

* Temperature: this variable has to be handled very carefully. If too high, the enzyme in yeast is denatured; when too low the reaction is slow so in order to make it a fair test the temperature should:

- Make the particles travel faster resulting to more collisions

- If the movement exceeds activation energy (energy required for movement of particles) then reaction speeds up

* Ph Level: the Ph level of yeast should be kept at an optimum to give a successful reaction.

To see the effect of temperature on the reaction! An increase in temperature increases the rate as the particles are given more energy to collide! But a certain amount of activation energy must be reached to let the particles collide between them and this is known as the collision theory.

The temperature also increases the potential for the enzyme in yeast that too speeds up the reaction.

The kinetic theory also explains that temperature increases the rate of a reaction as it makes the particles move faster after reaching a necessary amount of activation energy.

Activation energy is the amount of energy that must be reached for particles to collide between them.


The process that converts sugars (Glucose) into carbon dioxide and water. The general formula is:

Glucose ? Ethanol + Carbon Dioxide + Energy

C6H12O6 ? 2C2H5O + 2C02

As there is Carbon dioxide, we can say that the process is a kind of anaerobic respiration. Once yeast combines with sugar it starts to respire.

This reaction produces carbon dioxide, water and energy.

There is more energy in the anaerobic respiration because the energy that yeast needs from glucose is locked up in ethanol. After the concentration of ethanol reaches 12% the yeast dies so fermentation stops.

Yeast performs alcoholic fermentation. This is because after respiring anaerobicaly the reaction produces alcohol (instead of lactic acid in actual anaerobic respiration).

Since one of the products in fermentation is Ethanol this process is said to be alcoholic. For the yeast the useful product is the energy released the CO2 and alcohol are by products.

Alcohol has a very high energy content. This is a poisonous substance and the yeast excretes it into the surrounding liquid medium.

This is why baking is very necessary for bread as it kills yeast and fermentation stops. Otherwise bread would be alcoholic and poisonous.

2) Obtaining evidence

* The collision theory

For a reaction to take place the particles must collide with enough energy called the activation energy. If the collisions produces a lot of energy then the reaction were more likely to take place and it would speed up. For a successful experiment the particles must produce enough energy by collision and should collide in the right direction. Therefore, increasing the temperature would make the particles move faster and so produce more collisions resulting in the rate to speed up.

* The Kinetic theory

This theory focuses which highlights pressure, temperature and volume. It says that gases contain particles that are constantly in movement. They then exert pressure because the particles are colliding with the walls of the container. Decreasing the volume increases the pressure and vice versa.
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When the dough containing carbon dioxide and air is heated in an oven the volume of the gases increases resulting in the bread rising. This is because the particles are given a lot of energy to collide with each other and therefore hit the walls of the container and increase in volume. This is how temperature makes the dough rise faster as we increase it.

In this experiment, my aim is to see how the temperature affects the rate at which the dough rises and to find out the optimum temperature for the reaction. Yeast contains ...

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