C1b 5.3 Everyday Emulsions
What happens if you let ice cream melt and then re-freeze it?
Separates into crunchy ice crystals and a buttery oily part
Made from
two runny
liquids!
Oil, water
Egg yoke stops the oil and water from separating out
Egg yoke is an emulsifier
mayonnaise
ice cream
milk
salad
dressing
What do these substances have in common?
They are all……
OK – so what is an emulsion?
Emulsions are foods made from a mixture of oil
and water and they are important foods as they
Oil
are smooth and creamy.
droplet
Water
But, oil and water don’t mix (immiscible) so we need a
special substance which stops the water and oil
separating out.
We need an EMULSIFIER
Emulsifiers stop oil and water from separating
out, but how do they work?
An emulsifier molecule
_
This end is attracted to oil
(Hydrophobic)
This end is attracted to water
(Hydrophilic)
water
oil
droplet
The charged oil droplets repel each other
(like charges repel), keeping them spread
throughout the water.
_
_
_
_
_
_
_
_
_
The negative charges repel
each other which stops the oil
droplets from coming together
and forming bigger drops.
_
_
Observing an emulsion (milk) with a microscope
Put a drop of one
type of milk in the
centre of the
microscope slide.
Place a cover slip
at the edge, and
support it with the
mounted needle.
Gently, lower onto
the liquid in order to
minimise air bubbles
getting trapped
underneath.
Put the slide onto the microscope
stage, and adjust for the lowest
magnification and bring into focus.
Repeat for other milk.
Draw diagrams of
what you see.