Store Cupboard Science for the Summer

We’ve some fun food science experiments for you to try over the summer holidays. No special equipment needed and you should be able to find everything you need in your kitchen cupboards.

Can you make flour puff up to create ‘puffy paint’?

 

Have you heard of ‘puffy paint’? Curious to find out what it is? Morgan and Tilly, our young food scientists discover how easy it is to make it using flour and a microwave and the knowledge of food science.

You’ll need –  self-raising flour, salt, food colouring, a mixing bowl, a clean paint tray, paper straws and a microwave oven – plus a bit of adult help.

Place two tablespoons of flour in a bowl with a pinch of salt.  Add enough cold water to make a smooth thin paste.  Divide the mix into six in the paint tray and add  different food colouring to each one to make coloured paste paints.  Stir well to combine.

Use the paper straws to paint onto plain paper.  Once you have finished painting place your pictures in the microwave and heat for 30 seconds – ask an adult to help you and make sure you watch whilst it’s being heated.

When it comes out, look what’s happened – the mixture has puffed up and is firm to touch.

Leave to dry.

 

 

 

 

Why did that happen?

Self-raising flour contains baking powder – which is a rising agent.

Mixing the self raising flour and water together creates a reaction which results in a gas Carbon Dioxide – CO2 being released, when

heated this expands making the paint puff up and the flour mix dries out leaving raised puffy paint which goes hard.

 

 

 

Changing the colour of your cuppa – without adding milk

 

Lots of us love to drinktea, it tastes great, but we’ve been using it in a fun food science experiment that investigates its colour. To try it yourself all you need is a mug (that is white on the inside), a teabag, some boiling water and a lemon or lemon juice.

Place your teabag into the mug and fill with hot water from the kettle (ask an adult to help you).
You need to make the tea in a mug with a white inside colour so you can see the colour changes.

Let it brew for a couple of minutes and take the teabag out.

Cut your lemon in half (or use lemon juice from a bottle).  Squeeze the lemon into the tea and
watch the tea change colour –we stirred the tea to make the colour change uniform across the liquid.

The more lemon juice you add the lighter the tea goes

 

 

 

 

Why the colour change?

 

The tea contains pigments which give it its colour – thearubigins – when we make tea they are a reddish/ brown colour.   If the water is acidic then the pigment changes to a lighter colour. As we have seen from our other Store Cupboard Science experiments lemon juice is acidic and by adding a squeeze of lemon juice to the tea we can change the colour of pigments.

 

 

Preparing fish to eat – no need to heat! 

 

Did you know you can use your knowledge of food science and acids to prepare fish to eat, without heating it?

We took our fresh fish (we used white fish) and cut it into small pieces and then placed it in a glass bowl , we then squeezed lemon juice over the raw fish.  We left for 15mins (covered over and in the fridge) and then checked the fish and turned it over.   After 30 minutes the fish was flaked and ready to eat. Look at the differences between the before and after – the fish takes on the appearance of being ‘cooked’.  We tried the fish and although it tasted very lemony it was flaked and no longer raw.

 

Before adding lemon juice –                         After marinading in lemon juice –

               

 

The Science Bit

When you cook a fish with heat the proteins in the fish denature (i.e. their structure changes) and turn white instead of translucent.  When the proteins denature their complex 3D structures unfold and change permanently and change orientation and this is what causes the changes in colour and texture.

 

When you use acid to prepare the fish the process is called ceviche and the acids denature the proteins by interacting with the side chains of the proteins.  The most commonly used acids are lime and lemon juice.  Unlike heating the fish there is no evaporation of moisture – but you can still ‘overcook’ fish if left in the acid for too long, which makes it rubbery.

 

For more details visit : Protein: acid denaturation | IFST