Heat 1 cup of milk to almost boiling in a pan, then take it off the burner.
Stir in 4 tsp of white vinegar and mix for one minute.
Pour it all into a strainer.
Scrape what’s left onto a paper towel. (It will have a gloppy consistency.)
Pat out the liquid. The more you get out, the sturdier the plastic will be.
Knead in food dye or glitter.
Mold it or press it into cookie cutters. We made fridge magnets and decorated the tops with paper måché, but here are a few other options:
- Christmas ornaments
- Candle holders
- Pots and saucers
- Hand-print tiles
How Does It Work?
When you add vinegar to your milk, it changes the acidity levels. The heat on the stove speeds up the reaction, and the casein proteins in the milk begin to separate and clump together—or coagulate—unfolding and reorganizing into a long chain called a polymer. Poly means many—and for good reason, because it’s a collection of all the single molecules (or monomers).
This long chain of molecules causes high molecular weight, which is why you can scoop the casein out and knead it like a dough.