“It still surprises me
that something as
simple as vigorous
mixing is enough to
shift things around on
a molecular scale”
ILLUSTRATOR: ANDREW LYONS
B
utter production is modern alchemy.
Those who know the craft can
convert a mundane white liquid into
a deliciously rich ingot of edible gold. I’ve
never really tried alchemy, unless you count
making ‘potions’ when I was six, using leaves
stolen from my mother’s precious geraniums.
But I’ve just tried making butter, and it’s easy.
All you have to do is to turn milk inside out.
It started when I put the butter back into
the fridge next to a pot of cream, and
wondered how much of one you needed to
make the other. I didn’t know, so I bought
some more cream and started whisking.
Cream and milk look smooth, but that’s
only because their structure is too small for us
to see. Both are mostly water, but the liquid is
carrying passengers: proteins and fat globules
that make up 5-10 per cent of the total (for
milk). The fatty treasure is made up of
hydrophobic molecules, which means that
they are repelled by water. To keep the water
at bay, the fat sits in little balloons made of
proteins and other molecules. This is an
emulsion, and it’s as close as you can get to
mixing fats or oils with water. The two types
of molecules don’t have to touch, because
their micro-packaging keeps them apart, but
every bit of water has fat globules in it.
When I started whisking, I forced all those
little balloons to whoosh past each other and
the whisk also pushed air down into the
mixture and made bubbles. So far, so good. If
a fatty balloon burst in the chaos, the fat
molecules could surround an air bubble
instead of mixing with the water. This is what
happens when you make whipped cream –
the whipping process breaks up some of the
fat globules and those fat molecules surround
and stabilise air bubbles. Instead of the bubbles
rising through the water to the surface and
being lost, they’re trapped by the fat and you
get lovely white foam.
It still surprises me that something as
simple as vigorous mixing is enough to shift
things around on a molecular scale. But after
a couple of minutes, I had a bowl of
whipped cream. I was just wondering
whether anything else was going to happen
when I noticed that a stripe of white specks
was collecting on the wall, and on me. The
contents of the bowl had suddenly gone
lumpy and were making a serious bid for
freedom. The fat globules had been joiningtogether as I’d been whisking and they’d
reached a magic threshold where they
couldn’t hold bubbles any more. The
bubbles had gone, the globules had grown
into lumps of butter, and the watery
buttermilk was just sloshing about at the
bottom of the bowl.
The oddest bit was washing the butter.
You need to rinse the buttermilk away, so
you put the butter in cold water and massageit a bit. It had never occurred to me that you
could wash butter, but of course it’s not going
to mix with the water you’re washing it with.
And there you are. Two pots of cream
produced about two Ping-Pong balls’ worth
of butter.
But I hadn’t washed away all the water.
Milk and cream are emulsions of fat in
water, and butter is the opposite: an
emulsion of water in fat. About 20 per cent
of commercial butter is little globules of
water that make an important difference to
the texture. The smaller they are, the
smoother the butter is. Once you’ve turned
your cream inside out, a beautiful buttery
golden reward is all yours.Take fat, water and add a little science to make your own butter
Comment & Analysis
DR HELEN CZERSKI is a physicist, oceanographer and BBC
science presenter whose most recent series is Super Senses