My final guest post this week comes from Emma at Science Sparks. Science Sparks is one of my ‘Must Go To’ blogs and I highly recommend that you pop over there for a root around once you have finished reading this post! Today Emma is making toffee apples and popping a bit of science in for good measure!
Hello, I’m Emma from Science Sparks and I’m very excited to be guest posting on Thinly Spread today.
Science Sparks is a blog full of fun and easy science based activities for young children, so please come and take a look around if you haven’t already.
Autumn is my favourite time of year, I actually quite like it when the nights start to draw in, when outside is cold but inside is cosy and warm. Two of the things from my childhood I associate most with this time of year are toffee apples and treacle toffee, both of which are great for demonstrating changes of state.
Please be careful when cooking toffee apples as the sugar needs to get very hot!
How to Make Homemade Toffee Apples
200g golden caster sugar
1/2 teaspoon of vinegar
2 tbsp golden syrup
- Cover the apples with boiling water for a few minutes, this removes the waxy coating so the toffee will stick better. Dry the apples, remove the stalks and push a lollypop stick or wooden skewer into the apple.
- Add the sugar and 50ml of water to a pan and heat for about 5 minutes stirring gently. The sugar will melt and the two liquids combine.
- Stir in the vinegar and syrup.
- If you have a cooking thermometer ( we didn’t ) boil the sugar mixture to 146 C. This is called the ‘hard crack‘ stage. You can test whether the sugar is at the correct temperature by dropping a little into a bowl of cold water. If the toffee hardens immediately and can be snapped when removed it is ready.
- Very carefully pour the toffee over each apple and leave to harden on a non stick mat or baking parchment.
What do you think of our apples?
As we made the apples I showed the children the sugar in its solid state and asked them how they thought we could melt it. My 4 year old wanted to leave it out in the sun, but we decided heating on the hob might be faster.
As the sugar melted we could smell a toffee like smell and as it got hotter and hotter we saw more and more bubbles.
Once the apples had been dipped in the toffee I asked the children what they thought would happen as the toffee cooled down.
The Science Behind Making Toffee Apples
This experiment is a great way to demonstrate the process of changing state from solid to liquid and back again.
Everything we know exists in three states: A solid, A liquid or a Gas!
Substances can change from one state to another by different processes.
SOLID ––> LIQUID = MELTING
LIQUID ––> GAS = EVAPORATING/BOILING
GAS ––> LIQUID = CONDENSING
LIQUID ––> SOLID = COOLING/FREEZING
When the sugar was heated it changed from solid to liquid which is an example of melting and when we move back from a liquid into a solid it is an example of cooling/freezing.
The reason this happens is because when you provide heat the particles that make up the solid are given energy which cause them to vibrate which breaks the bonds holding them together. As they cool they lose this energy and so forms bonds again but not in the same shape.
When the sugar and water solution reaches the hard crack stage there is almost no water left. This is the temperature lollipops and toffee are heated to. At lower temperatures softer candies are made.
A much simpler way to demonstrate changes of state would be to melt chocolate and make rice krispie cakes!
Watch out for a whole host of candy themed experiments coming soon on Science Sparks.