A-maiz-ing - The Science of Popcorn - Part 2

A-maiz-ing - The Science of Popcorn - Part 2
Teachers Notes
This activity can be used to investigate how different preparations
(treatments) can affect the volume of the popped maize. Comparisons
can be made between different treatments. You may wish to give
students the facts sheet Explaining the popcorn explosion before they
design their experiment. All material has been designed to be
photocopied for classroom use.
What is special about popcorn?
Types of corn and how to prepare in advance.
Hydrated corn
This can be made by soaking normal
popping maize in water overnight. Drain and
pat dry before use. Unpopped popcorn
bought in shops contains approximately
14% water. This is the optimal water content
for popping maize. By soaking it overnight,
the water content in the kernel is raised above
the optimum level.
Broken maize
Maize can be slightly damaged by placing it
in a transparent plastic bag and cracking the
pericarp with a rolling pin. You are aiming to
damage the pericarp without breaking the
kernels open. Popping maize requires a
high pressure to build up in the kernel.
If the pericarp (outer casing) is broken, this
high pressure cannot be maintained and
the maize will not pop.
Non-popping maize
Maize that is used for feeding animals can
be obtained from pet shops. You may need to
extract these from a mixed feed. Starch
granules in popcorn are very tightly packed
within the cells. This tight packing is
essential for popping. Other varieties
have less tightly packed starch.
Normal popcorn
Popcorn can be bought in bags ready to pop
from most supermarkets. Do not use
microwave popcorn.
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Risk assessment
It is necessary to reinforce the message to students that even though
the laboratory where the experiment is done may be clean. It is not good
practice to consume food which has been in the laboratory.
Because of the high temperatures involved in popping maize, the equipment
used is likely to be hot.
Suggested Equipment
Measuring cylinders (of varying volume 10 — 20 cm3 for unpopped maize and 50 — 100 cm3 for
popped samples). Popcorn machine or heavy based saucepan with lid and oil for popping.
Popcorn machines can be purchased at many catalogue stores. These do not require the use of
oil and normally cost £15 — 25 each.
Predictions
You may wish to go through the information on Explaining the Popcorn Explosion with
students before they make their predictions.
Method
Measure a small volume of each sample, approximately 10 cm3. Record this initial volume
in the table. Pop each of the samples if you are using a popcorn machine, follow the
manufacturer s instructions). Otherwise heat 10 cm3 of oil in the pan and then add one sample of
the maize, cover and place on a high heat. As soon as the maize starts popping, turn the heat
down and wait for popping to stop. Measure the volume of popped maize and record the final
volume in the table. In each case a time limit should be recorded for the control sample and
maintained when popping other samples. You should make sure that the maize is popped
at the approximately same temperature to make it a fair test.
By using the results table to determine changes in volume, the students will be able to make a fair
comparison of different samples.
Observations and discussion points;
Some popping may occur in all cases. However, the volume of the normal popcorn will
be greater than that of the other maize samples.
The normal popcorn can be used as a comparison and is called a control .
Students may be asked to:
Æ make comparisons between samples
Æ use their observations and results to
draw conclusions
Æ judge level of uncertainty in observations
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