Food Molecules






Students will learn how molecules react in physical and chemical changes through examples of familiar food by baking bread and making butter


What are food molecules?
How can we change carbohydrates, proteins, and fats when we make food?


Tablecloth or cutting boards for small sanitary workspace
Large mixing bowl
Small bowl

Food molecules sheet

Sourdough starter
Flour, water, salt
Bread that has risen and is ready to be baked Jam (optional)
Baking sheet
Parchment paper
Oven access

Examples of fats: olive oil, coconut oil
Heavy cream
Jar for shaking (with a clean marble or pebble)


Preheat the oven and lay out materials on a spare, clean table.

Distribute a food molecule worksheet or display one on the board/projector so students can follow along with the discussion.

What is a molecule? Can you name one?
-Look at a simple water molecule. How small are they? Why can we see water with our eyes? Look at a size comparison chart of atom to what we can see with our eye.
-What are some of the other molecules present in food? Today we’ll be focusing on carbohydrates, proteins, and fats, and observing how they change when we make food.

What is a ​chemical change​? What is a ​physical change​?
Today, we’ll be looking at examples of both: chemical change: baking bread; physical change: making butter.

-What is a sourdough starter? Have students observe/smell/pass around the sourdough starter.

-Is it alive? What is in there?
Look and smell the dry commercial yeast. Have a volunteer come up and activate the commercial yeast. Pass it around and compare to the starter.

Have a volunteer come up and feed the sourdough starter, if needed.
What do you think are the pros and cons of using activated yeast versus a sourdough starter?
Compare diagrams of a bacteria and a fungal/yeast cell. What are these, and what role do they have in making bread?
Write out the equation for fermentation. What are the inputs? What is the product? What is causing the change?
Have volunteers come up to shape the dough for baking – take it out of the bowl, put it on a parchment paper baking sheet, place in the oven for 25 minutes (shape it into a flat shape for quick baking).
Compare homemade bread to typical bread from the store. What ingredients do you see? Can you pronounce them? Are these ingredients meant to help your body or help keep bread on the shelf for longer?
Observe the glycemic index of different bread type charts. Where does sourdough bread fall on the index? How about white bread versus whole grain bread?
Review: What type of change is this? What food molecules are we working with?

Observe the fats on the table. Are all types of fat the same? How do you know? Observe the ​saturated fats​. These typically stay solid at room temperature, like coconut oil, butter, animal fats (like in steak), cocoa butter, etc.

Observe molecular structure of saturated fats. They’re saturated with hydrogen!

Now look at the ​unsaturated fats​. These are typically liquid at room temperature, like olive oil, avocado oil, sesame oil

Observe molecular structure of unsaturated fats. They’re ​not​ saturated with hydrogen and form bent structures

What type of fat is butter? What do you need to make butter?
Discuss different fat content of different cows milk, how we as a country use Holsteins, even though other cows are said to produce better tasting butter

Review; what is the change here? What are the food molecules involved?

Finally, you can all eat bread and butter together!


This lesson covers a lot of topics, and can be expanded or truncated easily. It can even be part of a larger unit. Below are some ideas on how to use this lesson as a jumping off point:

Nutrition – whole grains versus processed grains, fermented foods and their nutritional benefits, microbiome and gut health.

Observation and lab examining differences in commercial yeast and a sourdough starter, under microscope, experimentation baking breads with the sourdough versus commercial method, implications for health and the food system.

You can have students delve deeper into the sourdough bread baking process. They can feed the starter, make a levain, observe a risen levain, make the dough, and they can observe a risen dough (this requires more prep for you at home to have bread at all stages for the class like a cooking show).

Observation and lab examining differences in butter made from factory farmed milk versus butter made from cream from local cows, examination of cream under microscope. Explore the implications for health and the food system and lead a discussion on genetically modified cows and proteins of different cow breeds and their digestibility.

Use observations and lab time to explore the fat difference in other animal fats. Making butter (a physical change) and then reversing the change in the same class