Shower cakes
Scientific principle Crosslinking Time required 30 minutes plus 3 hours setting time This recipe is not edible
Make bath time much more fun by washing with your personally designed, and scientifically crosslinked, wobbly shower cakes!
Equipment
Silicone muffin tin or small round plastic container
Ingredients
3g (1 tsp) gelatin
60ml (1⁄4 cup) boiling water 85g (1⁄2 cup) bar soap 1 drop food colouring 1 drop olive oil
Instructions
1. Carefully pour the boiling water into a bowl and add the gelatin, stirring until completely dissolved.
2. Add the oil and food colouring.
3. Grate the soap and add to the bowl, stirring gently to mix.
4. Carefully pour the mixture into a silicone muffin tin or plastic container.
5. Refrigerate for 3 hours.
6. Use in your next shower.
7. Store in an airtight container to stop the cake from evaporating.
Science behind the shower cakes Gelatin is made up of coiled up proteins, which are unique because they can be heated up to 100degC without breaking down or denaturing. When gelatin is dissolved in hot water, the protein chains unravel and stretch, floating around in the water. As the water cools, the gelatin strands start to coil again, but they become tangled with other gelatin chains, trapping some of the water inside their coiled structures as they do so, through weak bonds called hydrogen bonds. This process is called crosslinking. The coiling results in the soapy water getting caught in between the molecules so it cannot move freely anymore and the mixture transforms from a liquid to a gel. As you rub the gel on your skin in the shower, the friction or rubbing help to release the soap and water from the gel on to your body.
Explore further
What happens when you mix more or less of the gelatin into the hot water? How does the structure of the shower cake change? Why do you think this is?
Can you add other ingredients such as glitter or peppermint oil to your cakes to add some sparkle and scent?
What happens if you don’t store your shower cake in an airtight container? Why do you think this happens?