The Science of Yeast

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SWBAT explore, discover and develop a simple understanding of the chemical changes that yeast goes through when activated.

Big Idea

Observing and understanding the chemical changes that can happen within a chemical is exciting. Understanding what causes that change is confusing until you understand the science behind it.

Setting the Stage

5 minutes

This lesson is taught during the short week of Thanksgiving. It is an engaging set of lessons that incorporates history, art, and science.  

The days that lead up to the first big holiday break for most students are busy.  Teachers run into snags in planning their days, when they do not have a full week to work, but still have many requirements in teaching that need to be addressed.  However, the children are already beginning to have the mindset of vacation.  This means a teacher needs to have a really strong and engaging lesson planned to keep that momentum of learning going.  The fun smells and reactions that yeast can bring give this lesson it's punch and enough excitement to keep the kids focused and learning.  

It offers students the opportunity to explore setting up and conducting an entire investigation and using the senses to make distinctions of observable properties of yeast (PS1-1).

Engage (Day 1)

5 minutes

I pose the question..."Did the Pilgrims and Indians eat bread at the first Thanksgiving?" This simple question actually sets the stage for entire investigation (SP1). 

The question is on the screen. The Power Point is a great visual for those students who need to have the words on the screen.  

Classroom conversation ranges from a myriad of ideas: the Pilgrims brought it with them on the Mayflower, to the Indians made it.  However, none of the children are really too sure how the Pilgrims or the Indians made their bread.  They do know that there are different ingredients, but to name the ingredients escapes them.  

I explain that we are going to spend the next couple of days learning about bread and what it takes to make it.  Many eyebrows go up and I am sure they are wondering where this lesson will lead.  I continue to explain to the children that there is one small ingredient that makes bread become more than just a food we eat, but truly an amazing observation of science.  

Explore (Day 1)

10 minutes

I bring out a slice of bread and show it to the children.  I explain to the children that we are going to look at a bread with our jewelers loops.  The children are excited, they love to use the loops and enjoy getting to observe different items with them.  

I ask each team leader to come and gather materials for their team: a plastic picnic plate, slices of bread, jewelers loops, sketching paper and black ink pens.  The team leaders take the materials back to their teams and distribute the materials to each member.  The children are very accustomed to working in teams and the leaders have had enough practice to know instantly to pass out materials quickly. 

The children are sketching their observation on small pieces of paper.  Usually a quarter of a regular sized 8 1/2" X 11" page.  I explain that we will glue these into our journals when we are finished with our work.  

The plastic picnic plates work well as science trays for specimens and observations.  They are easy to store and clean up.  This makes management in the classroom much simpler.  

The children are familiar and comfortable with using the jewelers loops. I remind them to only observe one place on the bread slice and sketch what they are observing.  They love using the ink pens and refer often to the scientist visitor who shared with us that she only sketches in black ink. It is a huge connection for the children when they refer to her.  The sketch allows the children to develop a simple model of their observation (SP2). 

The children become quite excited when they begin to observe the bread.  They see so many tunnels and pathways inside the bread.  The comments are so fun to hear....

"OH! wow!!! this reminds me of a maze."  

I open my browser on my computer and navigate to the Red Star Yeast website.  It is full of great information explaining the science of yeast.  It is not written for Second Grade students to read, but provides a great opportunity to practice gathering scientific information from media to explain natural phenomenons (SP8). 

After reading through some of the information, the children are quite intrigued to find out what else we are going to do with the yeast. I then flip my screen back to the Power Point and show the children slide six. It has magnified pictures of yeast.  I want the children to understand that a living breathing organism does not have to be large, but can be quite small and still have a significant impact on the world.  

Explain (Day 1)

20 minutes

After the children have had a chance to explore the slice of bread, I explain to them that there is one very important ingredient that is responsible for creating all those pathways and is called yeast.  

Slide five than asks...."What is yeast?"

By now, most of the children know that it is an ingredient in the bread and that it can have amazing results.  But they really are not sure how it works.  This is when the lesson becomes very exciting.  

I show the children this short video clip....

The video clip does an amazing job of explaining in a simple and engaging way the effects of yeast. It also incorporates new vocabulary that is important to the science behind yeast.  

After watching the video clip, I ask the children several clarifying questions to make sure they understood what they saw in the video clip. 

1.  Is the yeast a living organism? (yes)

2.  What did the young woman say would be necessary to use to wake up the yeast? (warm water)

3.  What does the yeast like to eat? (sugar)

4.  What does the yeast create after it eats the sugar? (carbon dioxide)

Beyond this, if the children pick up any other information from the video clip, I am thrilled. However, these answers are what I am searching for.  I want to make sure they understand that the yeast is alive, but that it must be "activated" in order to awaken or it cannot complete it's process.  I also want them to know that the sugar is an essential part of the process. 

At this point, I explain to the children that we are going to stop at this step and pick up the next day.  There are sounds of, "Do we have to? Can't we please keep going?" 

Which means it is a perfect time to stop.  I have them where I want them. Motivated and asking their own questions.  A sneaky trick, yes, but also an essential teacher strategy to keep them guessing!!


Elaborate (Day 2)

15 minutes

We begin the day reviewing what we learned about the day before. The children are excited and remember a lot of what we discussed. 

I explain that during our lesson today, we are going to be working with the yeast more.  I pull out a small packet of active dry yeast that I purchase at my local grocery store.  I explain to the children that yeast has been used for thousands of years and it has been found in history all the way back to the Egyptian culture.  The children do not have a strong sense of time when it comes to history this far back, but many of them are able to connect it to their own experiences with learning in their church training. 

I begin the power point on slide seven which shows simple pictures with math symbols that reiterate what happens with the combination of sugar and yeast.  It is what the young woman in the video from Day One explains happens when the two are combined.  

So far, the children have not actually seen the process in person, but only on screen in the video.  In this portion of the lesson, we will activate the yeast and watch it's reactions.  

I turn on my document camera and enlarge it as much as possible. I open the small package of dry yeast and pour it into a bowl.  I want the children to see it first hand.  After we look at it up close, I tell them I will bring to each of them a small sample to observe with their loops.  

I circulate throughout the classroom and pour a small amount on the children's observation plates. They immediately begin observing and instantly comments of, "OH! wow! can you smell that?" "It reminds me of bread."  "No, it is like pizza dough."  The children are instantly making connections to their personal worlds.  

The children begin sketching a second time.  This sketch is not the bread, but the actual yeast. The children glue their sketches in to their journals underneath the bread sketch.  

I tell the children that when a scientist wants to see something that is microscopic, they sometimes will make a slide of the organism or whatever it is to view under a microscope.  I suggest, "What if we made microscope slides with our yeast specimens so we can keep them and look at them anytime?"  

The children are ecstatic and cannot wait!!! While the children continue to work on their sketches, I move from child to child helping them to make their slide.  The slides are really just clear packing tape that we fold over with the specimen inside.  The children tape the specimen into their journals right next to their sketch.  Including the actual yeast specimen into the journal also allows the children the opportunity to have the actual sample right next to the model (SP2). 

Evaluate (Day 2)

20 minutes

After all this has been completed, I gather all the children around the document camera again and I explain that the last part of our investigation will be to activate our yeast.  I have warm water waiting and pour it into the bowl that is holding our yeast.  The children are all watching closely. They know what will happen because they instantly remember the information from the video the day before.  

Within minutes, the yeast begins to bubble up and have a reaction.  The smell of the yeast is also very strong and aromatic. The children begin to make comments about the smell and the actual reaction they are seeing.  

The temperature of the yeast also begins to rise and I have each child hold the cup with the activated yeast in their hands.  They can feel the temperature rising and they are surprised to feel it.  

After all the children have had a chance to hold on to it, I have the children go back to their seats and have the children practice explaining what happened when the yeast was activated with the warm water (PS1-4). 

I hear the children using the actual vocabulary that has been introduced in the last two days. 

When the children are finished with their conversations, I go back to the original question that began our two days of discovery...Did the Pilgrims and Indians have bread at the first Thanksgiving?

The children are able to explain that they know from our other learning that yes, they did have bread, but they now have a much better understanding of where that bread came from.