25 February 2009

Meringues maybe

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


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?


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


The more you whisk…..


the more bubbles get trapped…..


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


to something that looks quite different.


‘mashed potato’


‘cotton wool’

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


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?


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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