# How Does the Changing Temperature Affect the Rate of Fermentation by Yeast.

How Does the Changing Temperature Affect the Rate of Fermentation by Yeast

Aim:

My aim is to find out the effect of changing temperature on the rate of fermentation by yeast.

Introduction:

Fermentation is another name for the production of energy from food without using oxygen.  When yeast ferments glucose the process can be represented by the following word equation –

Glucose         alcohol  + carbon dioxide + energy

Yeast is a single celled, microscopic fungus that uses sugar as food.  Yeast reproduces asexually by budding a ‘daughter’ cell.  This then becomes detached and follows an independent existence.  Fermentation is important in everyday life because it has a variety of uses. Brewers exploit fermentation to produce alcoholic drinks, and bakers use the carbon dioxide to make bread rise.  Key factors, which could affect the speed of fermentation, are temperature (which I am investigating), amount of yeast, amount of glucose solution and concentration of the glucose solution.  The rate of reaction could be measured by the amount of gas given off during fermentation – the number of bubbles or volume of gas.

Prediction:

I have chosen 5 temperatures or variables at which I will measure the  rate of fermentation: 20°C, 30°C, 40°C, 50°C and 60°C.  I think that the optimum temperature, where the rate of fermentation will be quickest is 40°C.  I think that the rate of reaction will be slow at 20°C and increasing at 30°C.  I think that above 40°C the reaction will slow down again.

Scientific reason:

All enzymes are made of protein, and proteins are denatured at high temperatures (above about 50°C). The rate of enzyme activity increases with temperature up to a maximum, then falls to zero as the enzyme is denatured.  The optimum temperature for reaction of enzymes is usually 40°C.  For a reaction to take place between two particles, they must collide, so if more collisions occur, the rate of reaction is higher and faster.  The rate of reaction will increase if the temperature is increased to its optimum temperature.  The heat energy gives particles more energy and so more particles will collide and react.  At lower temperatures the enzymes are much slower, and there are less collisions, and so the reaction is much slower.  At temperatures above 40°C, the enzymes start to lose their specific shape – the active site changes shape – which means that they cannot attack the substrate any longer and break it down.  Enzymes are completely denatured by 60°C.  It will be very difficult to ensure that my final conclusion is based on reliable data because I will not know whether my data is reliable or not unless I compare it with data from other experiments and see if my results differ greatly from other people’s results.

Plan:

Equipment list:

• Beaker
• Specimen bottles
• Delivery tubing and bung
• Thermometer
• Measuring cylinder
• Glass rod
• Syringe
• Bubble wrap
• Elastic bands
• Stop clock
• Fresh yeast
• Glucose solution
• Tub or trough of water

Step-by-step plan:

1. Add 2g of yeast to a specimen bottle.
2. Add 10cm³ of glucose solution 10% concentration.
3. Put specimen tubes in a beaker of water at the temperature at which you are going to ferment the yeast and glucose and check the temperature of the glucose solution – wait until it gets to gets to the same temperature as the water around it.
4. Add the yeast to the glucose and mix together with a glass rod to form a yeast suspension.
5. Set a stop clock for 3 minutes – to let the fermentation start.
6. Add bung and delivery tubing.
7. Put the specimen bottle in a beaker of water at the chosen temperature.
8. Insulate the beaker with bubble wrap.
9. Put thermometer in the beaker of water.
10. Put delivery tubing in a trough of water, or container of some sort.
11. Fill a measuring cylinder with water and place over the end of the delivery tubing when waiting time is over to collect the bubbles of gas from the fermentation process.
12. Use a stop clock to time 5 minutes.
13. At 5 minutes look at the measuring cylinder to note the volume of gas collected in the measuring cylinder.
14. Repeat with water at other temperatures.
15. Repeat each experiment 3 times.

Diagram:

See attached sheet.

Summary:

The variable that I will change in my investigation is the temperature at which the fermentation is taking place.  I have chosen a range of temperatures from 20ºC-60ºC to give a varied set of results for good analysis.  I will ensure that my experiment is kept fair by keeping the specified temperature constant, by making my timings as accurate as possible, and by using the same amount of yeast and glucose suspension each time.  I will be using 2g of yeast, 10cm³ of glucose solution  with a concentration of 10%.  I will give ...