Teachers Guide Scientriffic 81 - CSIRO

NAME ______________________________________________
Moo goo
CurriCulum links
Science understanding: Year 2, Year 4 and Year 6
chemical sciences
Science inquiry skills: Foundation – Year 4
Questioning and predicting, planning and
conducting
Aim
Make a sticky substance from milk and observe
its properties.
BACkground
Read the article ‘Tasty cheeses’ on pages 22–23
of Scientriffic.
CAution
Milk ‘glue’ will spoil after several days. It can
be kept in the fridge to increase its shelf life;
however, it should be disposed of when the
activity is complete.
You will need
• 2 cups
• 1 spoon for stirring
• Coffee filter paper or piece of thin rag
• 1 packet of powdered non-fat milk
• Vinegar
• Baking soda
• Measuring spoons
• Measuring cup
• Kitchen scales
• Hot water
• Cardboard or another material to test your
glue
whAt to do
1. Measure about ¼ cup of hot water into a
cup.
2. Add 2 tablespoons of powdered milk to the
water and stir until has completely dissolved.
3. Add a tablespoon of vinegar to the mixture.
Weigh the cup and the mixture on the scales.
Record the weight in the table.
4. Stir the mixture with the spoon. You should
see the milk begin to separate into solid
chunks of curd and a watery liquid called
whey. Stir until the milk is well separated.
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4 St | www.csiro.au/scientriffic | Scientriffic Teacher’s Guide | September 2012
5. Line the clean, empty second cup with the
coffee filter, and then pour the lumpy mixture
into the filter.
6. Lift the filter slowly. The liquid whey should
drain through the filter, leaving only the lumpy
curd.
7. Squeeze the filter containing the curds to
remove as much of the liquid whey as possible.
Put the curds into an empty plastic cup.
8. Weigh the cup with the curds. Record the
weight in the table.
9. Use the spoon to break the curds into small
pieces.
Material Weight (grams)
cup + milk powder + vinegar
cup + curds
• Roughly how much of the milk mixture is
made of curds?
• How much of the milk mixture is whey?
• Do you think milk from all mammals would
produce the same amounts of curds and
whey? How might milk be different in
different mammals?
10. Add one teaspoon of hot water and about
¼ teaspoon of baking soda to the curd and
mix thoroughly. You should see some slight
foaming or bubbling. Keep mixing until the curd
becomes smoother and more liquid.
11. The curd has now become glue. Test your glue
by sticking together two sheets of cardboard.
Milk reacts with an acid like vinegar to make a new
substance. The vinegar curdles the solids in milk,
and then the rubbery solid is separated from the
liquid part of the milk. The curds dry to form a hard
plastic-like substance called casein plastic. After
the casein is separated from the whey by filtering,
baking soda is added to neutralize the acid. When
the curd no longer has acid in it, it returns to a more
liquid form. The foaming you see when the baking
soda is added to the curd is carbon dioxide gas,
which is made when the baking soda reacts with
the acid in the vinegar. The resulting liquefied casein
protein is our natural glue.