Did you know that milk (along with a few other common ingredients) can be used to make glue? What fun!

Here's a few recipes that you can try with your kids next time Science Fair season rolls around at school:

Simple Milk Glue
Ingredients:
1 Enameled pot (non-metallic)
500ml skim milk
90ml vinegar
60ml water
15ml baking soda

Method:
1) Heat milk and vinegar slowly, stirring constantly until milk begins to curdle (separate).
2) Remove from heat and continue stirring until curdling stops.
3) Let the mixture sit until all the curds (thick white bits) have settled to the bottom.
4) Strain the curds or pour off the liquid (whey).
5) Place the curds on newspaper or paper towel and allow to dry to a glue-ish consistency.
6) Mix curds, water and baking soda. The vingegar will react with the baking soda. Stir until bubbling stops.
7) Store glue in an air-tight container.

This glue will keep for a couple of days, but once it starts to smell like old milk you should probably throw it away. This applies to all these glues.


Simpler Glue
1) Add one cup of milk and 1/3 cup of vinegar to a mason jar.
2) Let stand until the milk separates.
3) Pour off the liquid (whey) and discard.
4) Add 1/4 cup of water and 1 tbsp of baking soda.
6) Mix and let stand until bubbling stops.

I haven't tried this glue but it seems much simpler than the recipe above and requires no cooking, which makes it easier and safer for the kids.


A bit more toxic Glue
Ingredients:
1tbsp low fat milk powder
80mL water
vinegar
ammonia

Method
1) Mix water and milk powder until dissolved.
2) Add drops of vinegar to mixture and stir until milk curdles.
3) Strain curd and allow to dry.
4) Add drops of ammonia to curd, stirring until creamy.

Haven't tried this one either; I'm allergic to ammonia. But it follows the same principles as the other recipes, except it uses ammonia as the base to neutralize the acidity of the vinegar. I'd stick with vinegar for the kids though.

Why it works
It's all about the Casein
All of the above recipes use milk as a source of casein, the active ingredient in this type of glue. Casein is a sticky protein composed of complex chains of amino acids that can be used to make glue as described above or even biodegradable plastics. But that's another node.


Sources:
http://www.zetatalk.com/shelter/tshlt21z.htm
http://www.tki.org.nz/r/science/scienceschool/resources/1999/milk_glue.htm
http://chemistry.about.com/cs/howtos/ht/gluefrommilk.htm