Yummy Science – Sticky Milk . Experiments you can try in the kitchen – Magical Water, Growing Crystals, Spud Guns, Designer Onions, Honeycomb Toffee, Toast Busters, Toasty Science,Custard Bouncing Balls, Self Slicing Banana, Secret Messages

Science Links

More fun nutrition activities at
the Rowett Research Institute, eduweb
Check out National Science & Engineering Week at:
The BA (British Association for the Advancement of Science)

Further food science ideas for the primary aged audience are presented in the ‘Food for Thought resource, downloadable at The BA

For secondary pupils, there are lots of great kitchen chemistry ideas available in the Salters Chemistry Club handbooks or in various publications produced by the Royal Society of Chemistry

Exploring the science:

Milk contains a variety of substances suspended in water but one of the main constituents of skimmed milk is the protein CASEIN. Adding vinegar to milk (changing the acidity) causes the Casein to polymerize i.e. the structure of the casein changes, long chained molecules are formed, and the casein comes out of solution. Plastics are well known polymers, they are usually made from petroleum oil but in this case, we have created a plastic made from milk.

At one time buttons were commonly made from casein ‘plastic’, nowadays petroleum-based plastic is used due largely to cost.

In the glue-making process, the bicarbonate of soda neutralizes the acid residue and causes the casein to become soluble again - not only soluble but now at a much higher concentration. Un-refrigerated glue will spoil after about 48 hours, discard when it develops a sour milk smell!

Taking it further:

What happens if you replace the vinegar with another acid? Such as lemon juice - try it and see.
Maybe you could find a way in which to colour your casein buttons?
How much of 1 litre of skimmed milk is actually curd solid? (do you need to use a litre of milk to find out?).
Test the strength of your glue - think up a test and compare the strength of your milk-based glue to other glues such as PVA & copydex.

Milk is amazing stuff did you know that you can use it to make a ‘natural’ plastic? You can even create buttons to sew on to your designer onion t-shirt! Vary the recipe slightly and you can use milk to make a really a strong glue. Sounds too good to believe? Here’s how to do it....

You’ll need:

Tub of dried skimmed milk powder
Vinegar (white vinegar preferably)
Coffee filter paper
Couple of clean empty jam jars or other suitable containers

And for the glue: Bicarbonate of soda

What to do:

Into one jam jar put 2 tablespoons of dried skimmed milk powder and mix with about 100mls of hot (about 60^oC) water.
Add 1 tablespoon (about 15 mls) of vinegar and stir well. The mixture should curdle. Leave it to stand for about 3 minutes - liquid and solid will begin to separate out.
Cover the top of the other jam jar with the coffee filter paper and filter the milk/vinegar mixture by pouring the liquid into the filter.
Discard the liquid but retain the solid residue on the coffee filter paper.

For buttons: Take a lump of residue, press into a thin layer and mould into the button shape of your choice don’t forget to make a couple of holes in your button for sewing on with a needle and thread. Put the button on a piece of aluminium foil and allow to dry overnight.

For glue: Scrape the residue into a clean container and add 1 tablespoon of warm water and half a teaspoon of bicarbonate of soda. Mix well for a couple of minutes until mixture is smooth.

What happens:

The milk curdles as the vinegar is added - effectively creating ‘curds’ (the solid) and ‘whey’ (the liquid). There should be sufficient curds to make some buttons AND glue.