Wednesday, April 25, 2012

Bread on the Rise Lab

Its lab time again! And this time we're doing microbiology using supplies you have in your kitchen and pantry. I did this lab with boys ages 13-18, but it can easily be adapted for younger students. Here is the STUDENT HANDOUT.

Overview of the Bread on the Rise Lab

Questions students try to answer in the lab: (Inquiry level = 1)  
  • What ingredient in bread makes it rise?
  • Can you increase the speed at which bread can rise?

Each student (or groups of students) has four small bread dough balls to manipulate an independent variable.  Some choose amount of water, sugar, flour, or yeast. Others see if artificial sweeteners work differently than sugar. What the student changes is up to them, They just need to be sure to keep everything else the same.

Teacher Preparation Notes

Make some dough ahead of time. 

I made mine approximately 2 hours before the beginning of my first lab. (It may be possible to use thawed Rhodes frozen dough, but I'm not sure whether the proportions of yeast will work. If someone tries this, let us know if students observe noticeable changes between their groups.) Directions for making dough from scratch:
This recipe is enough for 2 groups, adjust amounts accordingly. In a bowl, mix 1 cup of flour, 2 tsp of sugar, and 1 tsp of yeast. Very slowly add warm water a tablespoon at a time mixing with a large spoon until you can pick up the dough and kneed in more water. The dough should not stick to your hands or work surface. If its too sticky add more flour.  You can store the large mix of dough in an airtight container for hours (even overnight) just knead it before you separate it into smaller quantities for student groups.

Prepare student's workspace

For each group (2 or 3 students per group) prepare a work surface, either cafeteria tray or cutting board, and put flour and dough into cups, and set out 12 straws, teaspoon (or plastic spoon) and a ruler.  

Have the following materials for students to use, depending on their choice of independent variable. 
  • Flour
  • Sugar
  • Yeast (w/ 1/2 teaspoon for measuring) 
  • Artificial Sweetener (Splenda, Sweet & Low, or Equal)

Philosophy Behind the Lab

I modified this lab from a book called "Meet the Microbes" put out by the National Association of Biology Teachers. The lab was originally titled, "Yeast on the Rise," but I wanted to give kids the opportunity to test which ingredient makes bread rise. Here is some background to help you guide discussions during the prelab; lab and postlab. (From pg. 62)

Yeast are living organisms that require food, water, and a warm place to grow. They break down sugars as a food source for their energy needs and produce carbon dioxide gas and ethanol as waste products. This process is called fermentation.

Fermentation is important in the production of many food products such as bread, yogurt cheese, pickles, and sauerkraut. When flour is mixed with water, sugar, and yeast, the yeast feed on the sugar. As the yeast release carbon dioxide and alcohol, the gas becomes trapped as bubbles in the dough, causing it to rise. When the bread is baked, the gas is vaporized, leaving a honeycomb texture. 

The various types of bread vary not only because of the type of grain used (wheat, corn, rye) but also in how much yeast is used. Different cultures have their own variations of bread, such as pita bread, tortillas, and unleavened bread. 

Student Lab Experience

Here is the STUDENT HANDOUT. My students found that flattening the dough balls into "bowls" allowed them to add their ingredients more easily. 

Here are some samples of what my students choose to study. 

Exp. Group #1
Exp. Group #2
Exp. Group #3
No sugar
½ tsp sugar
1 tsp sugar
1 ½ sugar
No yeast
¼ tsp yeast
½ tsp yeast
¾ tsp yeast
Straws stored in room temperature
In the sun
In the fridge
In the freezer

Note, each mound of dough receives yeast, sugar and water, depending on what their independent variable.   

Encourage students to enjoy the messiness of combining the ingredients, and encourage them a find a way to keep each of the groups correctly identified.  

While students could just observe the three mounds of dough and watch and describe any changes, in order to quantify how much the breads rise, students will mark drinking straw at 3 cm and fill the straw to this line with dough. 

Getting the dough into the straw is easier said then done. Allow the students to find a method that best works for them. But encourage them to work quickly because they need to have all 12 straws filled within a 5 minute time period. (This is when working in groups is helpful.)   

The student version of the lab describes two ways to make stands for the straws. One is by using clothespins and the other using clay. We found the clothespins to be more trouble than they are worth.

However, clay worked well as stands for the straws. They held the straws upright, and allowed us to seal the bottom of the straw so we didn't have to pinch the dough above our 3 cm mark.

Students had the idea to color code the straws to their groups. For example; red stripe = control, green = exp. #1 etc.

Fair warning, make sure the bottom of the straw seals with the clay so that dough can't push out the bottom. This makes the measurements less accurate, as we are measuring  upward movement in the tube, not downward. 

Students collect their dough data measurements at 10, 20, and 30 minutes.

Since our straws weren't clear (I would recommend this if you have them laying around) we had trouble seeing the height of our dough. So we used lamps and window light to make it more clear.

I designed the student handout so students would have things to do while they wait between their 10 minute data collection times. During their first break they are making predictions of what dough groups will rise the most and least. And during their other breaks they are calculating the mean for the 3 straws of each group. They are also to graph their results, and they can be setting this up as they wait as well.

The post lab questions work to get student "talking" about their graphs, considering how procedure may have influenced results, and then discussing whether or not students' predictions were correct, and whether or not they could speed up the rising of bread. 

Science Sunday [Note: This activity is modified from a lab titled "Yeast on the Rise" put out by the National Association of Biology Teachers in 1999.]

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