Yeast Fermentation Essay Sample

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The purpose of this lab is to find out what effect has sugar on yeast in different concentrations of sugar.

Background information

Yeast is a fungus and needs a supply of energy for its living and growth. Sugar supplies this energy. Yeast can use oxygen to release the energy from sugar in the process called “respiration”. So, the more sugar there is, the more active the yeast will be and the faster its growth (up to a certain point – even yeast cannot grow in very strong sugar – such as honey).

However, if oxygen is short or not present, then yeast can still release energy from sugar, but in these conditions, its byproducts are alcohol and carbon dioxide. This process is called fermentation. To introduce this laboratory, a number of foods are produced by fermentation such as yogurt, buttermilk, yeast breads, sour cream, etc.

Sugars are the common substrate of fermentation. The alcohol and the carbon dioxide are waste products produced by the yeast, which we can see on the equation below.

C6H12O6 2CH3CH2OH + 2CO2 + Energy

Simple Sugar Etanol Carbon Dioxide

Table 1. Comparison of respiration and fermentation of sugar in




Products from sugar

Amount of ATP



6 CO2 + 6




CO2 + 2 C2H6O



If we limit the oxygen that is available for yeast reproduction and increase the amount of sugar the yeast can react with, we expect the yeast will use the sugar for energy and reproduction.


Yeast can extract more energy from sugar when oxygen is present in their environment. In the absence of oxygen, yeast switch to a process called fermentation. With fermentation, yeast can still get energy from sugar, but less energy is derived from each sugar molecule.

In this laboratory I will add the same amounts of yeast and water to different amounts of sugar in water bottles and cap them with a testing tube to see how much carbon dioxide gas is produced. The more the fermentation, the more the carbon dioxide will be produced.

Work cited:

Time Requirements

This lab will require three, days to complete.

Selecting variables

Independent variables: amount of sugar

Dependent variables: amount of CO2 produced

Controlled variables

Amount of yeast and water, the time for fermentation is the same – three days, the amount of both distilled and normal water.


* 5g dry yeast

* 10g sugar

* distilled water (room temperature, If the water is too hot (above 37C), the yeast will die)

* water

* three 500ml beakers

* three 80ml test tubes

* three 500ml flasks

* 3-finger clamps

* Ring stand

* 3 rubber stoppers

* Pencil

* scale


I make sure I will follow normal safety procedure during this lab

Each beaker is filled with 400ml of water.

Each flask is labeled: A, B, C

I put the certain amount of water, yeast and sugar into each flask as stated in the chart below:




200ml distilled water

200ml distilled water

200ml distilled


0.5g yeast

0.5g yeast

0.5g yeast

1g sugar

3g sugar

5g sugar

Allow the yeast suspension to incubate for 5 minutes, with occasional swirling.

Each flask is stoppered with a 1-hole rubber stopper containing a short tube that is attached to a long piece of tubing; the end of this tubing outside of the flask is placed under water in a 250mL beaker. The yeast in this flask will use up the oxygen inside the flask and will ferment sugar to produce carbon dioxide. The CO2 will displace the remaining air. This flask will not contain oxygen after the first hour or two of the experiment. Shake up the culture in the flask to mix the yeast cells evenly. This is important in order to get consistent results.

Each test tube is filled up with tap water and fixed in a finger clamp on the ring stand up side down the bottom side is dipped into water in a beaker.

Each beaker is labeled by the same letter as on the flask that is connected to by tubing.

When the laboratory is set the time and the amount of water in testing tube is written down. Time is written down again at 12:00 and 15:00.

The second day data is written down three times during the day: 8:00, 12:00, 15:00 o’clock and the following third days in the morning at 8:00 only.

Finally, I cleaned up work area. Wash and dry the equipment and return all equipment to its proper place.

Error reduction

I made sure that the amount of yeast used in each fermentation flask was the same (because I used a scale). I tried to reduce air us much as possible by rubber stopper.

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