Summary Experiments with yeast, and baking soda and vinegar show how the yeast and bacteria in the starter make the bread/cake rise. Science content Chemistry: States of Matter, Properties of Materials (K-7) Chemistry: Chemical Changes (2, 7) Activities in this lesson Yeast eats sugar and makes gas Bacteria chemistry of sourdough bread / yeast cake Procedure Investigate the living things that are in the starter mixes of sourdough bread or traditional yeast cake/bread. Living things in the starter are yeast and a Lactobacillus bacteria. (There are some kinds of yeast and bacteria that make you sick, but there are plenty that are helpful to us, and these ones are helpful yeast and bacteria). The yeast and bacteria in here live well together, and the bacteria makes acid which stops other yeasts or bacteria from growing. So the starters can be kept for a long time. Activity to determine the role of the yeast in the starter mixture. Activity to determine the role of the bacteria in the starter mixture. Notes A little much information for grade 2/3 class. Suggest either missing out the molecule models explaining what is going on (the yeast starts bubbling rapidly, so don't need much time waiting for it). Or just do one of the activities. Grades taught Gr 2 Gr 3
