Friday, 3 August 2018

5 Minute STEM Activity 6 - Turn Black To White (well, almost...)

Science can't explain everything, but sometimes it has a very simple explanation for something that seems impossible. If you hit yeast extract (Marmite, Vegemite etc) it appears to change colour from very dark brown to very light tan colour, almost from black to white. But why?


Turn black to white.
Marmite Bashing. 

EQUIPMENT:
1 level teaspoon Yeast Extract - Marmite, Vegemite etc.
A spoon, fish slice or other utensil to hit the yeast extract with.
A plastic plate or shallow bowl - not a Melamine camping plate, it'll break. The softer sort of plastic.


1. What you choose to hit the Marmite with and what you put the Marmite on are important because the amount of noise could be gentle, or eardrum-shattering. Have a test hit and try to find 2 things that don't make an awful noise. Silicone is good and quiet.


2. Pour about 1 level teaspoon of Marmite onto your plate/bowl

3. Hit the Marmite and watch it change colour before your very eyes...


Okay, so you'll find if you are gentle and just stroke the Marmite the same happens. It isn't the hitting that does the colour change, it's actually because you are stretching the Marmite particles and air is getting trapped in between. It takes so long for the air bubbles to 'float' to the surface that you can keep going and.... Voila!


You are doing the same as 'whisking' and it is very easy to do with Marmite because is so sticky and heavy. It holds shape really well and traps the air. The bubbles aren't able to rise to the surface very quickly, so they build up and up until the amount of bubbles is so great, and the Marmite is so spread out, it looks like it has changed colour.



Adding air to most liquids makes them fluffy and the colour goes lighter, although sometimes it's harder to see. They also take up more space, are generally softer and a cup full would weigh less. You see this effect when we whisk eggs or cake mix. You can also find it when you rub shampoo onto your hair.

Scientists call adding air Aeration. Some products are whipped to add air before you buy them, including types of chocolate, mousse and Margaret Thatcher's greatest achievement, Mr Whippy Ice Cream...


I'm taking tomorrow off because I'm at the CBBC Summer Social in Liverpool (see my NorthWest Summer Holiday Round Up), but it gives you chance to catch up! You can find the first 5 of the 5 Minute STEM Activities at the links below:

Fish In The Tank
The Floating Arm Trick
The 5cm World Challenge
What Is Gluten?
How To Step Through A Hole In A Postcard


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