13 February 2021 | New Scientist | 51The back pages
TETIANAVI
TSENKO/ALAMYSam Wong is social media
editor and self-appointed
chief gourmand at
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These articles are
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newscientist.com/makerWhat you need
1 egg yolk
1 tbsp lemon juice
1 tsp Dijon mustard
250 ml vegetable oil
OIL and water famously don’t play
well together. Water is a polar
molecule, with a negative charge
concentrated around the oxygen
atom and a positive charge at the
two hydrogen atoms. This means
that water molecules attract each
other, the hydrogen atoms
forming bonds with the oxygen
atoms of nearby molecules. Oil,
on the other hand, is made from
non-polar molecules, which aren’t
attracted by the water molecules,
so it is hard for them to mingle.
If you shake oil and vinegar
vigorously enough, you can get
the vinegar to be dispersed as tiny
droplets in the oil, making what
is called an emulsion. But they are
likely to separate before long.
Chemicals called emulsifiers
can make the emulsion more
stable because an emulsifier
molecule has one pole (or part)
that loves oil and one that loves
water so it can form an interface
between oil and water. Mustard
plays this role well in a vinaigrette,
helping ensure the dressing
won’t separate so readily.
A vinaigrette that isn’t well
emulsified will make salad leaves
wilt quickly, because the oil can
get through the waxy cuticle of
the leaves. But if the oil droplets
are properly dispersed in vinegar,
with the help of mustard, the
leaves remain crisp for longer.
Egg yolks contain compounds
called lecithins that are very
effective as emulsifiers. These
allow large volumes of oil to
be suspended in a relatively
small amount of lemon juice to
make mayonnaise. Even thoughFrom eggs to mashed chickpeas, making great mayonnaise means
grappling with the chemistry of emulsions, says Sam WongScience of cooking
Marvellous mayonnaise
mayonnaise is mostly oil, it
doesn’t feel greasy because your
mouth senses only the so-called
continuous phase of the
emulsifying process – which
is water-based.
Proteins can also work as
emulsifiers, because they have
polar and non-polar parts too.
Vegan mayonnaise can be made
using a few mashed chickpeas and
some of the protein-rich liquid
from a tin of chickpeas, known
as aquafaba, instead of egg yolk.
In sauces such as gravy,
thickening agents like flour help
to create a stable emulsion. They
work differently: by increasing
the viscosity of water, they prevent
fat droplets from moving through
the liquid and coalescing.
The traditional way to make
mayonnaise starts by whiskingegg yolks with a bit of mustard
and lemon juice. The oil must be
added very slowly and whisked
in vigorously so it becomes
dispersed as droplets in the
water. If oil is added too quickly,
it forms a continuous phase on the
surface instead of an emulsion.
You can think of mayonnaise as
a template for making emulsion
sauces from any flavour you
like. Add an egg yolk to pureed
vegetables, garlic, herbs, miso
paste or anchovies, for example,
then add oil slowly in the same
way. For a fancy finishing touch
to your presentation, use a
squeezy bottle to put blobs
of emulsion sauce on the plate. ❚Feedback
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