Lesson plan

Chemistry of baking yeast cake

Experiments with yeast, then baking soda and vinegar show how gas is made while bread is made with a starter, and how they make the holes in the cake.
Science content
Chemistry: States of Matter, Properties of Materials (K-7)
Chemistry: Chemical Changes (2, 7)

What is in the starter mix that we used for making sourdough bread or traditional bread/yeast cake?
Today we will investigate the living things that are in here, and what they do.

What living things could be in there? They must be small...
Living things in this starter are yeast and 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 stop other yeasts or bacteria from growing.

Activity to determine the role of the yeast in the starter mixture.

Activity to determine the role of the bacteria in the starter mixture.

The starter has a yeast and a Lactobacillus bacteria in it.


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