8 February 2020 | New Scientist | 51IF THERE is someone you would
like to impress on Valentine’s day,
this swirly chocolate slab could be
just the thing. Simply melting and
mixing the chocolates won’t do,
however. To make glossy, smooth
chocolate with a pleasing snap,
you need a little knowledge of its
chemical structure.
The chocolate we know is a
far cry from the astringent cocoa
bean from which it originates.
The cacao tree has been cultivated
in Central America for more than
3000 years. Archaeologists have
found chemical traces of cacao on
pottery dating to 1600-1800 BC.
Cocoa beans grow in large pods
packed with fibrous, sugary pulp.
To make chocolate, the beans are
first fermented in the pulp. Bitter
phenolic compounds react and
form less bitter complexes, while
enzymes in the beans break
down sugars and proteins into
compounds that react more easily
in the next step: roasting. Maillard
reactions then produce the full,
complex flavour of chocolate.
The roasted beans are ground,
breaking the cells into particles
suspended in fat, known as
cocoa butter. The mixture can be
turned into chocolate by adding
ingredients such as sugar and
milk solids. It is then mechanically
worked in a process called
conching, before being cooled
into solid bars.
The texture of chocolate
is determined by the crystal
structure of the fat molecules.
The glossy surface and pleasing
snap of a good bar of chocolate
arise when the fat molecules alignin a dense network of compact
crystals. If chocolate melts and
resolidifies in an uncontrolled
way, the molecules form loose,
irregular crystals that result in
soft, mottled, crumbly chocolate.
Tempering is a way of creating
the right crystalline structure. You
will need a thermometer because
the key is to hold the temperature
at 31 to 32°C, which is below the
melting point of the right crystals
and above the melting point of the
wrong crystals.
Break or chop 300 grams of dark
chocolate into small pieces and
hold a few in reserve. Melt the rest
in a bowl over a pan of hot but not
boiling water. Once it is all melted,
remove from the heat and stir in
the reserved chocolate, which willseed the melted chocolate with the
right kind of crystals. Keep stirring
until the temperature falls to 31 to
32°C. Hold it at this temperature
until you are ready to use it.
Do the same with 300 grams of
white chocolate in a separate bowl,
but keep it at 27 to 28°C.
Line a tray with baking paper.
Pour in the dark chocolate, then
pour the white over the top. Use
a chopstick to make patterns and
ensure there are no holes in the
slab. Drop in some hazelnuts and
coffee beans – or anything else you
like – along with flakes of sea salt.
Let it cool at room temperature
to allow the crystalline structure
to develop fully. Wrap up the
whole slab as a gift, or break it
into pieces. ❚Understanding the structure of chocolate will give you mastery
over it, says Sam WongPuzzles
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JAMES
WINSPEARSam Wong is social media
editor at New Scientist.
Follow him @samwong1
Science of cooking Week 6
Chocolate magic
Science of cooking online
All projects are posted at
newscientist.com/cooking Email: [email protected]What you need
White chocolate
Dark chocolate
Thermometer
Hazelnuts
Coffee beans
Sea salt
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