Abstract
Dried beans are a major ingredient in dishes served all over the world. In their dried form, they can be stored for years and then "brought back to life" by soaking them in water. In this cooking and food science fair project, you will measure just how much water is absorbed by beans when they rehydrate (soak up water). Can such a little bean really hold that much water?Summary
David B. Whyte, PhD, Science Buddies
Objective
Measure how much water is absorbed by dried beans.
Introduction
Beans come in dozens of shapes, sizes, and colors, as shown in Figure 1, below, and have been consumed throughout the world for thousands of years. They are low in fat and are good sources of protein, carbohydrates, and fiber. The U.S. Department of Agriculture dietary guidelines suggest that beans, along with other foods that are low in fat, oils, and sugars (including fruits, vegetables, and grains) should make up the largest portion of our daily meals. Beans are a type of legume, which is a group of vegetables that also includes peas and lentils.
Figure 1. This picture shows a mixture of beans (including pinto beans, black beans, black-eyed peas, lima beans, and others) as well as peas (including green split peas and yellow split peas). (Wikimedia Commons, QuimGil, 1969)
In addition to their nutritious qualities, beans are convenient because they can be dried and stored for years. Soaking the beans in water for a few hours softens the dried beans and prepares them for cooking. This process of rehydration of dried beans also occurs in nature. Beans are a form of seed, and they can sprout and grow new plants when they are exposed to water. Beans stay viable (which means they are thought of as being "alive") for long periods of time if they are kept dry. This feature lets them survive long periods of drought in natural settings, and allows us to store them for long periods of time before cooking them.
As beans soak in water, their volume and mass increase. In this cooking and food science fair project, you will determine the amount of water that is absorbed by dried beans. The procedure calls for weighing the beans after they have soaked for different periods of time. You could discard the beans after they are weighed, or you could add them to a pot of water to soak overnight and make a bean-based recipe of your choice!
Terms and Concepts
- Legumes
- Rehydration
- Viable
- Mass
- Absorb
- Control
Questions
- What advantage does a plant whose seeds can survive for years in a dry environment have?
- How many kinds of dried beans are there at your local grocery store? How many have you tried?
- In nature, what role is played by the proteins and carbohydrates in a bean? Hint: Beans are seeds.
Bibliography
- Kids Health. (n.d.). So what's a legume?. Retrieved December 1, 2009.
For help creating graphs, try this website:
- National Center for Education Statistics. (n.d.). Create a Graph. Retrieved June 2, 2009.
Materials and Equipment
- Plastic cups, 12-ounce size (18)
- Permanent marker
- Dried beans, pinto (2 16-ounce bags)
- Scale, accurate to 1 gram (g), such as the digital pocket scale from Amazon.com
- Measuring cup, liquid, metric
- Water
- Lab notebook
- Timer or stopwatch
- Plastic wrap
- Strainer or colander
- Paper towels (1 roll)
- Adult helper
- Graph paper or an online graphing resource like Create a Graph
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Experimental Procedure
-
Label six plastic cups with the permanent marker, as follows:
- Cup #1: Zero
- Cup #2: 0.3 hour (20 minutes)
- Cup #3: 1 hour
- Cup #4: 3 hours
- Cup #5: 9 hours
- Cup #6: 27 hours
- Put one plastic cup onto the scale and zero the scale. Have an adult show you how to do this if you do not know how. Then weigh out and put 50 grams (g) of the dried beans into each of the six cups.
-
Add 100 mL of water to cups 2–6.
- Cup # 1 is a "no water" control. Having a control leads to more-trustworthy data.
-
Record the time that the water is added in your lab notebook.
- Choose a start time that will allow you to weigh the beans at the times listed above.
- Cover the cups with plastic wrap.
- After 20 minutes (0.3 hours), pour the contents of cup # 2 into a strainer.
- Shake as much water as you can off of the beans in the strainer.
- Pour the beans onto several sheets of paper towels.
- Gently dry the beans with the paper towels.
- Put a clean dry cup on the scale.
- Zero the scale.
- Add the beans that soaked for 20 minutes (from cup #2) to the cup on the scale.
- Record the weight of the beans from cup #2 in a data table, like Table 1, below, in your lab notebook.
| Soaking time | Mass for Trial #1 (in g) |
Mass for Trial #2 (in g) |
Mass for Trial #3 (in g) |
Average Mass (in g) |
|---|---|---|---|---|
| 0 | 50 | 50 | 50 | 50 |
| 0.3 hours | ||||
| 1 hour | ||||
| 3 hours | ||||
| 9 hours | ||||
| 27 hours |
-
Discard the beans from cup # 2 (or add them to a pot and soak them overnight for cooking).
- Describe the appearance of the beans in your lab notebook.
- Compare them to the beans in cup #1.
- Repeat steps 6–14 for cups 3–6, at the appropriate times (listed in step 1). Also weigh the beans from cup #1 when you are done comparing them to the soaked beans.
- Repeat the entire procedure two more times, for a total of three trials. This ensures that your results are accurate and can be repeated.
- Calculate the average masses. To do this, add the data from the three trials for each amount of time together, then divide by three (for three trials). Ask an adult if you need help with this step. How did the masses change over time?
- Graph the average mass of the beans over time. Put the mass (in grams) on the y-axis (the vertical axis) and the time (in hours) on the x-axis (the horizontal axis). You can do this by hand on graph paper, or use a website like Create a Graph.
Ask an Expert
Variations
- Compare water absorption by trying this science fair project with different kinds of beans, peas, and lentils.
- Determine the rate of water absorption, as follows. Subtract 50 g from the average weight, in grams, to get the weight of water absorbed. Divide the weight of water absorbed by the time in hours. Add this data to your table and graph the time (in hours) on the x-axis and the rate of absorption (in grams per hour) on the y-axis.
- Soak the beans at different temperatures. For example, soak them for 3 hours at 0°C (ice water), 30°C, 60°C, and 90°C (simmer in a pot on a stovetop). Compare the rates of rehydration at the various temperatures.
- Devise a procedure to measure the change in volume of the beans vs. time in water.
- See the Science Buddies science fair project Tough Beans: Which Cooking Liquids Slow Softening the Most? for a procedure to determine how soft the beans are after soaking in water.
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