Yeast
An experiment to demonstrate the effect of temperature on fermentation by yeast
The purpose of this laboratory is to observe how temperature affects the metabolism of
Grape juice by visibly noting the volume changes of identical food mixes containing yeast at different temperatures.
Background Information
If yeast is added to a liquid containing sugar and other nutrients, kept at an appropriate temperature (and deprived of oxygen), it will turn the sugars into ethanol (alcohol) and carbon dioxide.
Apparatus and Materials
Waterbaths set to a range of values - 10, 20, 30, 40, 50, 60, 70 °C
Thermometer
1 x 200 ml beaker - preferably marked on side
7 x test tubes
7 x 10 ml measuring cylinders
7 x Rubber bungs to fit the measuring cylinder & test tubes
Forceps
700 ml grape juice (Red)
70 ml yeast suspension
Plastic rod for mixing
Ice
Method
Step Method Justification
1 Prior to the experiment, make sure that the grape juice is shaken or mixed.
2 Set up a waterbath of 10 °C of the above. Place a thermometer in the waterbath.
3 Add either ice or hot water, to the waterbath to make sure the required temperature in achieved.
4 Measure out 100 ml the grape juice into the 200 ml beaker using markings on the side of the beaker as a guide.
5 Pour the contents of the 200 ml beaker in a measuring cylinder
6 Mix the yeast suspension using the plastic rod, and add 10 ml of the yeast suspension to the grape juice in the measuring cylinder.
10 ml fills so as to completely fill it, not just to the top of the measurement lines)
7 Place a rubber bung in the cylinder, and with a thumb on the rubber bung, shake the tube vigorously for 5 seconds.
8 Invert the measuring cylinder and place it in the water bath.
9 Examine the thermometer and ice or hot water should be added so that the temperature of investigation is correct.
10 Using forceps, remove the bung, ensuring that mouth of the measuring cylinder is still under the liquid.
The purpose of this laboratory is to observe how temperature affects the metabolism of
Grape juice by visibly noting the volume changes of identical food mixes containing yeast at different temperatures.
Background Information
If yeast is added to a liquid containing sugar and other nutrients, kept at an appropriate temperature (and deprived of oxygen), it will turn the sugars into ethanol (alcohol) and carbon dioxide.
Apparatus and Materials
Waterbaths set to a range of values - 10, 20, 30, 40, 50, 60, 70 °C
Thermometer
1 x 200 ml beaker - preferably marked on side
7 x test tubes
7 x 10 ml measuring cylinders
7 x Rubber bungs to fit the measuring cylinder & test tubes
Forceps
700 ml grape juice (Red)
70 ml yeast suspension
Plastic rod for mixing
Ice
Method
Step Method Justification
1 Prior to the experiment, make sure that the grape juice is shaken or mixed.
2 Set up a waterbath of 10 °C of the above. Place a thermometer in the waterbath.
3 Add either ice or hot water, to the waterbath to make sure the required temperature in achieved.
4 Measure out 100 ml the grape juice into the 200 ml beaker using markings on the side of the beaker as a guide.
5 Pour the contents of the 200 ml beaker in a measuring cylinder
6 Mix the yeast suspension using the plastic rod, and add 10 ml of the yeast suspension to the grape juice in the measuring cylinder.
10 ml fills so as to completely fill it, not just to the top of the measurement lines)
7 Place a rubber bung in the cylinder, and with a thumb on the rubber bung, shake the tube vigorously for 5 seconds.
8 Invert the measuring cylinder and place it in the water bath.
9 Examine the thermometer and ice or hot water should be added so that the temperature of investigation is correct.
10 Using forceps, remove the bung, ensuring that mouth of the measuring cylinder is still under the liquid.