25 April 2020 | New Scientist | 51BEING trapped inside has led many
of us to rummage in our kitchen
cupboards in search of inspiration.
I suspect I’m not the only one who
found a tin of condensed milk that
I’m not sure why I bought. If you
also have a neglected tin, there
are few more delicious things you
can make than dulce de leche.
Meaning “sweet of milk”, dulce
de leche is a kind of caramel sauce
that is popular in South America.
The traditional method begins
with milk, but using condensed
milk speeds up the process.
Condensed milk is milk in which
about 60 per cent of the water
has been evaporated, and sugar
has been added. Evaporated
milk is similar but unsweetened,
so it won’t work for this.
Remove the label and put the
tin on its side in a large pot and
cover with water. Then simmer
it for 2 to 3 hours, depending on
how dark you like your caramel.
It is crucial the tin is submerged
the whole time because this
stops overheating causing a
pressure build-up and a potential
explosion. Liquid water won’t
exceed 100°C, so a submerged tin
won’t get hotter than this either.
When the time is up, use tongs
to take the tin out of the water.
Make sure you let the tin cool
completely before opening it, or
else hot dulce de leche could shoot
out. The sweetened milk will have
turned into a thick brown paste
that you can spread on toast or
spoon on to fruit or ice cream.
Strictly speaking, the reaction
responsible isn’t caramelisation.
This term describes what happenswhen sugar molecules break apart
and generate a range of other
flavour compounds. This happens
only for sucrose – table sugar – at
temperatures above 170°C.
Just as with caramelised onions,
which I covered a few weeks ago,
the chemical process here is the
Maillard reaction. This occurs
when sugars react with amino
acids, the components that make
up proteins, which are abundant
in milk. The products are a range
of flavoursome compounds.
Maillard reactions happen
at lower temperatures than
caramelisation, but are quite
slow until you get to about 120°C.
In condensed milk, the high
concentration of compounds
for reactions and the prolongedcooking time can achieve
browning even at 100°C.
You can also make dulce de leche
the more traditional way, with a
litre of milk and 250 grams of sugar,
gently simmered on the stove. This
takes many hours but can be sped
up with a teaspoon of bicarbonate
of soda, which raises the pH,
accelerating the Maillard reaction.
Even so, it may take 2 hours,
and needs frequent stirring.
Alternatively, try cajeta, a
version made with goat’s milk,
which needs a mere 45 minutes or
so of simmering. Goat’s milk is
lower in lactose than cow’s milk,
so it is less likely to burn, and has a
higher concentration of various
amino acids, which confer thermal
stability and umami taste. ❚Dulce de leche is a supreme comfort food that is easy to make
when you are stuck indoors, says Sam WongPuzzles
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Follow him @samwong1Science of cooking Week 17
Sweeter and sweeter
Science of cooking online
All projects are posted at
newscientist.com/cooking Email: [email protected]What you need
Can of condensed milk
or
Milk
Sugar
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