PRACTICAL WORK

Five practical activities are described; they have been found to work well under class conditions and demand few resources. Most provide ample scope for manipulating variables and could be formatted into an Sc l framework. Other investigations, varying in complexity, are described in the bioreactor/fermenter kits referred to later in the booklet as well as in various texts.

List of practical activities

1, What happens when yeast and glucose are mixed?

2. Making your own wine.

3. Making your own yoghurt
(NB this has a 7-8 hour fermentation time and thus is difficult to programme; however, the recipe is suitable for students to try at home, with the added advantage that the product could then be consumed).

4. Can yeast respire without air?

5. Does temperature change affect the respiration rate of yeast?

Four of the investigations use yeast. In view of the unpredictable behaviour of commercially available yeast sources, especially after some time in storage, it is recommended that more than one brand of yeast be held in stock and that a trial be carried out a day or so in advance, to confirm activity/efficacy.

Yeast suspension should be made by making the dried yeast into a paste with a little water and then adding the remaining water to this paste, stirring thoroughly.

The addition of 5 g of vitamin C per 100 g of yeast suspension helps to optimise activity.