For a science fair project examining how the sugar in the banana changes as it ripens, you need five dark green, unripe bananas similar in size for each of three trials, a metal fork and knife, a plate (not paper, foam or plastic), (15) 6-inch squares of cheesecloth, scissors, a handheld refractometer, a camera and a lab notebook with graph paper. If you decide to run the three trials of this experiment concurrently, purchase 15 unripe bananas, instead of five, at a time.
Cut a three-inch long piece of one banana. Take a picture of the banana, and label it with the date, to document the changes in the color of the peels as the experiment progresses. Add the pictures to the science fair display. Peel the banana section, and place the piece on the plate. Thoroughly mash the banana piece with the fork. Enclose about one-third of the mashed banana in each of three squares of cheesecloth. Slowly squeeze one of the cheesecloth squares, and allow several drops of banana juice to fall onto the refractometer lens. Read the refractometer through the eyepiece. Record the measurement in degrees Brix (ºBrix), a unit that describes the ratio of dissolved sugar-to-water of a solution. Clean the refractometer according to manufacturer's directions. Repeat the process with each of the two remaining cheesecloth squares. Discard the used cheesecloth squares. Record the average of each day's three readings.
Repeat the procedure approximately every two days, using a different banana. You may adjust the testing schedule if the bananas ripen faster, or slower. At the end of the trials, plot the results on a graph. Put the days on the x-axis, and the ºBrix on the y-axis. Include the pictures of the bananas used for each test coordinated with their position on the graph, the refractometer and the lab results in the Science Fair display. Optionally, include a seven-stage banana ripeness chart showing the progression from dark green to yellow, spotted banana.
To see if temperature affects the ripening process, perform the experiment with bananas stored at various temperatures. Do not change any other variables, such as humidity.
Repeat the experiment to compare bananas stored in a closed paper bag to bananas stored in an open paper bag.
Compare the ripening of bruised bananas to un-bruised bananas. (Hint-Bruised bananas emit higher amounts of ethylene gas.)
Repeat the experiment to measure the difference in ripening between bananas in a sealed container, and bananas in no container. Keep the other experiment variables, such as temperature, humidity and size of the bananas, the same between the two groups of bananas (Hint-More ethylene stays close to a banana in a closed container.)
Label six spots on a paper plate with one of each number, 1 through 6. These represent the stages of ripeness for a banana. Starting with the unripe bananas, slice each one into 10 pieces, and put a toothpick into each one to facilitate handling. Unripe bananas are safe to eat. Place one slice on each paper plate in the number "1" spot. Repeat the process with each ripening stage of the remaining bananas. Divide the testers into groups of two. Blindfold one partner of each group. The other partner will randomly give the taster one sample at a time, making sure the taster drinks a bit of water or milk between each sample. After testing all six samples, the taster must tell his partner which one he liked best. The tester will circle that number of the paper plate. The partners should switch places and repeat the test. Make a bar graph showing the various stages of ripening, and how many tasters preferred each one. According to the Chiquita Brands, the majority of individuals prefer to eat bananas that are yellow with green tips and necks, or yellow with a green neck.