25 February 2009

Meringues maybe

When we made ice cream we cracked eggs and separated the yellow yolk from the ‘white’ or albumen.

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Remember how we whisked the ‘white’?  Let’s take another look.  What is happening when you whisk something?  What are you doing to it?  Look closely; what do you see?

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‘B u b b l e s !’  Yes, whisking puts bubbles in and the stretchy, sticky egg ‘white’ traps them.

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The more you whisk…..

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the more bubbles get trapped…..

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until it has changed from a clear slippery liquid…..

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to something that looks quite different.

Like:

‘mashed potato’

‘snow’

‘cotton wool’

Will those bubbles stay there forever?  Let’s look again after 15 minutes.  What do you see?

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Ah ha; there is some liquid that seems to have ‘leaked out’ of the foam.  Now put your ear really close to the foam.  What do you hear?  A kind of fizzy hissing noise; bubbles popping perhaps?

Do you think that if we leave it in the classroom overnight, all the liquid ‘white’ will have leaked back out; that all the bubbles will have popped?  Will it have gone back to how it was before we did all that whisking?

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Perhaps unsurprisingly, the heat of the classroom has had the effect of a cool oven; it has dried the white foam until now it is hard; it breaks into powder when you touch it.  The once-liquid part has also dried to a crisp transparent film a bit like when glue dries.

Maybe we have invented a new low-energy way of making meringues…..now where’s the (whipped) cream?

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