3. Baking and brewing
All living things respire and the respiration of yeast forms the basis of the brewing and baking industries. Case study 3 and Activity 3 show how you can make use of this in your classroom. In the case study, the teacher gets a visitor into the classroom and the activity involves a visit. While it requires time and careful planning, a visit to a local industry (e.g. bread making) will have real value in motivating students and in helping them to understand the relevance of what they do in class to the real world. It should also help them to realise that ordinary people have used aspects of the scientific process to refine their methods. Over hundreds of years scientists have observed, carefully experimented with different methods, evaluated the results and where necessary modified their methods. Before you go, try to prime students on what they should look out for. It will help if they have studied yeast and fermentation before they go and are asked to relate what they see to what they have learned.
Case study 3: Inviting a visitor to school
One of Mr Nkala’s former students, David, had started working in a local bakery. Mr Nkala asked David to come and talk to his students about work in the bakery. David enjoyed his job and was pleased to do this.
He explained that the main ingredients of bread are flour, yeast, and water. He had brought some fresh yeast and some dried yeast to show the students. He put some of the yeast in a small bowl, added some warm water and a small spoonful of sugar. He asked the students to keep an eye on the mixture to see if they noticed any changes. In the meantime, he explained how to make bread.
David told the class that yeast is a single-celled fungus. Like all living organisms, yeast gets its energy during respiration. He asked them what they knew about respiration and was impressed with the replies. Yeast can respire without the need for oxygen (anaerobic respiration). As it respires yeast produces carbon dioxide gas and alcohol.
By now the students had noticed that the bowl of yeast, water and sugar had started to froth up with lots of tiny bubbles. David had brought some samples of the bread he made which he passed round for the students to examine. He asked the students why the bread did not taste of alcohol. Before he left, David explained what qualifications he had and described the training he had received. One day he hopes to own his own bakery and intends to specialise in making different kinds of bread from other countries. He gave the class a recipe for making bread (Resource 5) which they could do at home.
Activity 3: Organising a visit
Set up an experiment to show that yeast, sugar and water produce carbon dioxide and ethanol, provided that they are kept in a warm environment, in the absence of air. Explain to your students how this process is used in bread making and in brewing.
Try to arrange a visit to a local bakery or brewery, to reinforce learning and demonstrate the practical uses of this process. Depending on the size of your local bakery or brewery, there may not be enough space for the whole class to go on the visit. Those who do go could give a short presentation to the rest of the class when they return. You and your students will need to be aware of strict rules on cleanliness and hygiene associated with any business concerned with food. You can ask your students to look out for ways the bakery workers ensure that cleanliness is maintained. Some equipment and processes could cause injury to your students, such as the hot ovens, so it is important that they act responsibly and listen to instructions carefully. During the visit students should try to find answers to a number of questions. Possible questions, together with suggested answers are included in Resource 6 . Students should also be encouraged to think of and to ask questions of their own.