New_Scientist_May_27_2017

MENTION the words “science” and “cooking”
in the same sentence and the phrase “molecular
gastronomy” springs to mind. Scientific
techniques have added zest to high-end cuisine, but
you don’t have to be using liquid nitrogen, spherification
and the like to benefit. Home cooks can learn a lot from
science, especially when it comes to knowing which bits
of kitchen folklore are worth swallowing.
It turns out that many top tips make little difference,
while others undermine flavour or even increase the risk
of food poisoning. We’ve sifted through some of the most
commonly promoted techniques, chewed over the
science and put the tips to the test to figure out which
should be saved and which should be thrown away.
SEARMEATTOLOCKINJUICES
Many chefs say to sear meat first at
a high heat to trap moisture. But if
you cook identical steaks to the same
internal temperature, one that is
roasted then seared is often juicier
than one that is seared then roasted.
Why? Higher heat makes the muscle
fibres contract more, forcing liquid out.
A cold steak takes longer to sear in a hot
pan than a steak that has been warmed
in the oven, so loses more liquid.
To retain moisture, the most
important step is to rest the meat after
cooking. As muscle fibres cool, they
widen, holding on to more juice.
Searing does boost flavour by
browning the outside. This is caused by
Maillard reactions: as sugars and
amino acids react, usually under heat,
they produce a huge range of flavour
compounds that contribute to the
distinctive tastes of everything from
roast beef to popcorn. It is Maillard
reactions that turn bread into toast
and provide the savoury crunch of
roast potatoes. But they also produce
acrylamide – particularly in starchy
foods cooked at high temperatures.
In the body, acrylamide is converted
into glycidamide, which can bind to
DNA and cause mutations. In animal
studies, consuming acrylamide has
been shown to cause cancers.
There is less certainty about its
effects on us, and whether the amounts
we consume are dangerous. Still, to be
safe, the UK’s Food Standards Agency
says to limit acrylamide exposure by
aiming for golden, rather than brown,
with foods like roast potatoes and toast.
COOKPASTAATAROLLINGBOIL
Many Italian chefs say you must add
pasta to a big pot of water at a vigorous
boil. This is because it will return to the
boil quicker and the extra room stops
the pasta sticking together.
It’s true that adding a set amount of
pasta to a smaller pot will lower the
water temperature more than adding it
to a bigger pot. But returning to a boil
takes the same amount of energy and
may even be quicker in a smaller pot
because it has less surface area.
As for sticking, this only happens
during the first minute or so of
cooking, when surface starch granules
swell and pop. Stir the pasta for the first
minute and you can happily leave it to
cook in your small pot. In fact, you can
turn the heat off and leave the lid on
and it will cook just fine, as starch
gelatinises at about 82°C, well below
water’s 100°C boiling point.
RISOTTO:NEVERSTOPSTIRRING
To make risotto, you must add stock
slowly and stir constantly, right?
Traditionalists are adamant that doing
so ensures even cooking and the perfect
creamy consistency.
This creaminess comes from
dissolving starch. Rice contains two
forms: amylose, made of long, straight
chains packed tightly together, and
amylopectin, which has a branching
structure. Constant stirring and the
slow addition of stock are supposed to
help dislodge amylopectin – by rubbing
rice grains against each other and
pushing liquid through gaps in the
branches. The amylose stays tightly
packed, so the rice retains some bite.
But chef J. Kenji Lopez-Alt, author
of The Food Lab: Better home cooking
through science, points out that most
of the starch that thickens risotto
comes from fine particles on the grains’
surface and it is the addition of liquid,
not stirring, that mostly affects its
release. (If you rinse the rice before you
cook it, the starch comes off and you
get a risotto with little creaminess.)
Lopez-Alt found that vigorous stirring
for a couple of minutes at the end of
cooking gives equally creamy results.
Still, traditionalists have a point, says
Matt Hartings, who teaches a chemistry
of cooking course at the American
University in Washington DC. The
higher the ratio of released starch to
liquid in the pot, the thicker the risotto
will be. Adding stock gradually gives
you more control over that ratio. “But if
you control your ingredients just right
from the outset, a no-stir method
should give you the creaminess that
you’re looking for,” he says.
AVOIDCERTAINOILSFORFRYING
Don’t fry in olive oil. This common
advice is based on its low smoke
point of around 165 to 190°C. When
the oil is heated to this temperature,
fat molecules get oxidised, producing
aldehydes and other compounds that
can be toxic and give an acrid flavour. >
MARCUS NILSSON/GALLERYSTOCK
27 May 2017 | NewScientist | 33