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 oC

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 oC 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