GOAL
Kids realize the benefits of an
engineered environment.
GRADE LEVEL
Elementary
IMPORTANT: Before planning
this activity for a classroom, ask
if the school permits food to be
brought in and if there are special
restrictions.
MATERIALS
(per group of 3-4)
Quart-sized zip top plastic bag
Gallon-sized zip top plastic bag
Ice cubes
Salt
½ c. half & half
½ c. whipping cream
3 ½ T. sugar
¼ t. vanilla (optional)
Rubber spatula, mixing spoons, plastic spoons, small cups
DISCUSSION
When ice starts to melt, it is 32 degrees. This is not cold
enough to freeze ice cream. Adding salt actually pushes the
temperature of melting ice down below 10 degrees Fahrenheit
(F). Heat flows from the ice cream ingredients to the melting
ice. The melting ice warms up while the ice cream becomes
cold enough to freeze. Shaking the bag does two things. It
brings warmer ingredients in the middle into contact with
the cold outside and speeds up the freezing process. It also
makes the liquid ingredients mix with air. The air makes the
ice cream soft and light—enabling this to be soft enough to
eat with a spoon even though it is frozen!
ACTIVITY
TIP: keep towels or
paper towels handy.
Step 1
Divide class into groups
of 3-4. Help children
measure the ingredients
(you might need to pour
liquid for the youngest
kids.) Have children place
half & half, whipping
cream, sugar, and vanilla,
in the smaller bag. Zip bag and place inside the larger one.
Step 2
Pack ice inside larger bag around the smaller one. Pour at
least ¼ cup of table salt evenly over ice. Seal large bag.
Step 3
Now the fun begins! Kids take turns
to manipulate and shake their bag.
(Use gloves or wrap towel around
outer bag. It gets very cold!) Check
consistency of ice cream. If, after
15 minutes of shaking, it is not yet a
solid, drain excess water from larger
bag and add more ice and salt.
Shake for a few more minutes.
Remove ice cream bag from the
larger one and quickly rinse with
cold water before opening. (This
removes the salt.) Divide ice cream
into cups and enjoy!!
QUESTIONS TO ASK
After placing liquids in the smaller
bag…Is this ice cream yet? What do we need to make it ice
cream? Why? Before shaking the bags…What do you think
will happen to the white liquid? Why? When shaking…What
is happening to the liquid? When eating…How does this
taste? Would you like to make your own ice cream every time
you want some?
FURTHER EXPLORATION
Try making ice cream
without adding salt to
the ice. How does this
affect the process? You
could also have one
group do the activity
as a “control” group
without using salt –
although be sure to have
a batch of ice cream in
reserve so this group
can join in the tasting
later!
CONNECT TO ENGINEERING
Before engineers invented machines to stir the ice cream
mixture, making this treat was an expensive, labor-intensive
local effort. With the advent of refrigeration techniques,
especially the continuous process freezer in the 1920’s, large
scale manufacturing and transport of ice cream became
possible. Engineers design machines that make tasty—and
sometimes far-out—ice cream flavors possible, mixing and
swirling flavors and the right amounts of candy and filling
into each container.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Chair of
Engineers Week 2011, helps keep indoor environments comfortable, preserve the outdoor
environment, and deliver healthy food to consumers.
ICE CREAM SPECIAL
