Weird Science: Scrumptious Slime

A hilariously horrific activity the kids will go bats about this Halloween!  This slime flows like a liquid but can be rolled like a solid – and the best part is that it’s edible!

Scientific Principle: Viscosity                

Time: ​45 minutes cooking time, 2 hours cooling time 

Equipment & Ingredients

  • Saucepan
  • Plastic sandwich bag
  • 395g (14 oz) can sweetened condensed milk
  • 10g (1 Tbsp) cornflour/cornstarch
  • 45ml (3 Tbsp) chocolate syrup


  1. Pour the milk into the saucepan and heat on a low heat.
  2. Slowly stir the cornflour into the warm milk. Continue heating and stirring over a low heat for 20 minutes or until the mixture thickens.
  3. Remove from the heat and stir in the chocolate syrup.
  4. Place in a sandwich bag and refrigerate.
  5. Once cold, roll and squeeze into any slimy shape you want – and watch it flow!

The Science Behind Edible Slime

Cornflour or cornstarch is a starch made up of long chains of sugar molecules called glucose which are joined together in a coiled-up ball. When exposed to heat and milk, the starch particles absorb water from the milk, causing them to swell. These swollen particles start to press up against each other. This reduces the movement of the liquid, resulting in it thickening or becoming more viscous. Eventually the starch particles burst, freeing up long strands of starch which swell further and absorb the fluid outside the particles. This traps the remaining water in the mixture and turns it into a highly viscous gel or slime. The slime flows like a thick liquid but can be rolled around like a soft solid. The advantage of this recipe is that the slime is edible once you have finished with it!

Explore Further

» What edible treats could you add to your slime to add more texture? Does this change the way that it flows?

» How does the slime flow differently when it is warm compared to when it is cold? Why is this?

» Can you think of other ingredients you could add, instead of the chocolate sauce, to make different flavoured edible slime?

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