The science of crispy: how to make perfect pork crackling

Health

What is it that turns tough pork skin into amazing crackling? Sam Wong reveals the secret to that wonderful crispy crunch

1 April 2020

What you need

Pork belly

Salt (optional)

Vinegar (optional)

BECAUSE of the environmental impact of livestock farming, I don’t cook meat often. But I can’t resist the occasional roast. Pork belly is one of my favourites – the only challenge is getting the skin to go crispy. Can science guide me towards the perfect crunch?

The internet has plenty of tips for ultimate crackling, but few provide a scientific rationale and many are contradictory. I decided to do some research and tests.

Pork skin is about 30 per cent collagen, a strong, tough protein made up of three molecular chains wound into a triple helix. Heating it for long enough breaks it down into gelatin, which melts away.

To make pork skin crisp, all the collagen must break down. You also need the skin to completely dry out and remaining proteins to coagulate and stiffen.

According to The Food Lab by J. Kenji LÓpez-Alt, the key to achieving all three is to start by slow-roasting the meat at a lower temperature, ensuring that the skin is well softened. Then blast it with high heat, so that pockets of air and steam under the skin expand and stretch it, making it thinner. The high heat will quickly firm the skin and make it crispy.

The US television cooking show America’s Test Kitchen agrees that slow-cooking, then rapidly evaporating the remaining water in the skin to make it puff up, is what is needed. But it says the oven can’t do the second part quickly enough. Instead it recommends in a pan at that point.

Home cooks in China favour yet another technique that draws on restaurant methods. They start by then poke lots of holes in the skin. These allow moisture and fat to escape during roasting. Some recipes advise bathing the pork skin-down in vinegar overnight, which may help weaken collagen.

There is another slight variant: before roasting, you can wrap the meat in foil, leaving the top open, and cover the skin in a thin layer of salt to draw out water. Some way through cooking, the salt is scraped off and the meat goes back into a very hot oven to crisp the skin.

I tested these methods on four 400-gram pork belly pieces. All joints were roasted for 2 hours at 130°C, skin side up. Then, one came out to be pan-fried while the others stayed in for half an hour at 240°C.

The vinegar-soaked piece had a smoother surface, while the others formed bubbly, blistered crusts. The salt-covered pieces were slightly harder than the others, but all were excellent: crunchy yet easy on the teeth.

Without having tested a shorter cooking time, I can’t be certain but I suspect the key to success was to give the meat plenty of time in the oven to break down the collagen before applying a blast of high heat to finish off. Bear in mind that timings will need adjusting for larger pieces of meat.

Next week

Protein from plants: seitan, a form of wheat gluten, is a great alternative to meat - and you can make your own

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