The first law of thermodynamics as it relates to delicious swine

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November 23, 2013 // Pork

There is no topic more steeped in swine-related folklore than the holy grail of delicious oinky goodness: crackling. We have spent the past year conducting an exhaustive study into the science of crackling it in order to sort grandma’s fiction from the science of piggy perfection. Our journey has taken us through the fields of thermodynamics and burns medicine.

This post is 90% rant so the TL;DR is if you want to cook this:

The Tunnel of Love

Read this: Perfect Crackling – TwoPorkSwords Style

The secret is all in the type of heat you subject the surface of the skin to, and how you go about managing the temperature gradient when you cook. Everything else is a sideshow.

Crackling myths and pseudoscience

Firstly, let’s take grandma’s folklore out back and shoot it. Almost every ‘guide to perfect crackling’ mindlessly follows a few techniques, none of which our testing showed as making a jot of difference to the end result.

Myth #1: Pouring water to render the skin/fat

Whether you pour boiling water over the skin or not makes zero difference to the end result. A jug/kettle of water renders our almost no fat and just makes your kitchen smell like damp pork. It does not help make crackling.

Summary: Folklore. Use if you like the smell of damp pork.

Myth #2: Boiling the rind

Closely related to the above, some people propose that you put the rind-side down in a shallow pan and boil it prior to cooking. Similarly to pouring boiling water over the rind, this makes no difference. It has the added effect of par-boiling the meat itself.

Summary: Folklore. Also ruins the meat in the process.

Myth #3: Rubbing oil all over the skin

This myth appears to be followed by the less observant who probably haven’t noticed that the giant lump of pork rind they are preparing is really just a giant lump of fat held together by some skin. How does rubbing fat on some fat help you get the end result you’re after? Beats us too.

Summary: Mostly a waste of time. You might need a small amount of oil to make the salt adhere.

Myth #4: Start with a really hot oven

This is the most common myth and the most incorrect. We had very little success in reliably making quality crackling with a normal fan-forced oven. Ovens generally deliver the wrong kind of heat and nowhere near the control you need for reliably creating a defect free surface of perfect crackling.

Summary: Unless you have a very expensive/commercial oven you’re likely to burn whatever is facing the fan and achieve no crackling with the other side.

Myth #5: Leave it in the fridge overnight with salt on it

One common crackling preparation theme that comes up is the need to extract as much moisture as possible from the rind. Again, in all of our year long programme of testing, this made no difference. We did once lay the rind face down on a bed of rock salt overnight near the cold air exhaust in the fridge. By the next morning the skin was like leather, most of the moisture had been drawn out of the meat, and the overall presentation of the cut looked like some sort of pork from a zombie. Cooking it only made it worse.

Summary: Worse than folklore. This is a sure-fire way to ruin your dinner before you even light the BBQ.

Myth #6: Put lots of salt on

People do this ostensibly to draw moisture out of the skin. Whether you salt the rind or not makes no difference to the crackling. Lots of salt does however make the crackling delicious.

Summary: False for crackling; True for delicious piggy.

Myth #7: Do X then cut the skin off and cook it Y

This plan starts from the principle that you don’t know what you’re doing – at all – and expect the cracking to fail and then need repair.

Summary: Failure is not a plan.

Let’s seek some professional advice!

And by professional advice, I mean a collection of random and made up opinions. You would think that a professional restaurateur, quoted in The Sydney Morning Herald might know what they’re on about, wouldn’t you? Well, clap your peepers on this:

A catastrophe of epic porkportions

Someone was actually proud of themselves for publishing this disaster in the Sydney Morning Herald.

Someone phone PETA, because if this isn’t animal cruelty, then I don’t know what is. It is mind boggling someone would actually put this picture on the Internet with pride. There is 2 square centimeters of average crackling on the bottom right of the entire surface, the rest of it would be like chewing on the cover of an old Gideon Bible. The chef responsible for that catastrophe should hang their head in shame. The full horror inflicted on this otherwise delicious piece of meat is recounted here: http://www.smh.com.au/lifestyle/homestyle/blogs/tried-and-tasted/the-quest-for-the-perfect-roast-pork-20110711-1haas.html

Read the ‘expert advice’ throughout the article. Lemon juice (WTF), oil, vinegar – why not wave a dead chicken over it too to see if that helps? It gets worse in the comments.

The only thing you can take away from this is that all of these people are doing what grandma said in the hope that a light and fluffy slab of cracking will emerge. Importantly, no one explains the actual reason they can get crackling. Again, it is all down to the method of heat transfer.

Heat transfer and the first law of thermodynamics

Everyone who operates a BBQ or oven should understand this.

There are three means by which heat can be transferred in the kitchen. Convection, conduction, and radiation (http://en.wikipedia.org/wiki/Heat_transfer). One of these is the answer for perfect crackling.

Convection: This is what happens in a fan forced oven. A heating element makes the air hot, the air is pushed around whatever it is your cooking and transfers heat. Convection is a pain in the proverbial. It is hard to control the temperature gradient. If you want to intervene in the cooking process you’ll lose all of the heat in the oven. Convection cooking is what all advice on the Internet recommends you use for crackling. Convection is used in all the myths above. CONVECTION CRACKLING IS A LIE.

Conduction: Heat transfer by conduction is what happens when you put something cold (i.e. a piece of meat) on something static and hot (i.e. a frying pan). It goes without saying this is not suitable for crackling purposes.

Radiant heat in action. My old Nexus 4 didn't have a very good IR filter so you can see the radiant heat coming off the coals.

Radiant heat in action. My old Nexus 4 didn’t have a very good IR filter so you can see the radiant heat coming off the coals. Note this is cooking kebab meat – NEVER wrap your pork in tin foil!

Radiation: Radiation is the transfer of heat by electromagnetic waves. Sounds complex? It isn’t. Examples of radiative heating include sunshine, cooking under a grill, cooking over heat beads. Radiative heat transfer is the answer for crackling. You can control the heating of the surface of the rind instantly by rotisserie or adjusting the grill temperature. Radiant heat won’t overly heat the meat so you can separate the slow cooking of the pork from the creation of delicious crackling through the fast cooking of the surface.

Perfect Crackling – TwoPorkSwords Style

The Theory

The sort of result you can expect under an electric grill. It can go pear shaped really quickly so you need to watch it closely. To achieve the s-curse you just pull it out from under the grill periodically.

The sort of result you can expect under an electric grill. It can go pear shaped really quickly so you need to watch it closely. To achieve the s-curve you just pull it out from under the grill periodically.

Lemon and salt and whatever other voodoo you’ve read about is irrelevant (except for taste!) – this is all you need to know. You need to heat the rind of the pork in what is called an s-curve of temperature. You need to do this using mainly radiant heat. This means you are heating the rind up, then as the heat builds you remove it from the heat just short of it burning but don’t let it cool down too much, and apply heat again. You need to watch what you are doing closely however you will be rewarded with perfect crackling, across 100% of the surface of the rind, every single time without exception.

You will achieve the best result with a rotissorie/spit roaster. No need to spend up big, a $70 unit from your local hardware/outdoor like Bunning’s Jumbuck Spit Roaster (http://www.bunnings.com.au/jumbuck-spit-roaster_p3180333) will do perfectly.

We’ve applied the same theory to an electric oven grill and it worked perfectly though you need to watch it like a hawk.

The process

Choosing the breed and cut of pork

The TwoPorkSwords method works with any pork with rind on. You will, however, get a much better result if you choose a quality piece of pork with a decent backing of fat behind the skin. We recommend a boneless pork shoulder, rolled and tied. If you a looking for a great breed, then Bangalow Sweet Pork (http://sweetpork.com.au/) are the go-to people. This collective of farmers is committed to breeding beautifully flavoured sweet pork in contrast to the ultra-lean and flavourless meat you’ll get at Coles or Woollies. We get ours from the James Street markets (http://www.jamesstmarket.com.au/). You will be amazed by the sweet flavour – it is unlike any other breed of pork you’ve had.

Bangalow Sweet Pork

Bangalow Sweet Pork

Step 1: Setting up and flavouring

We like our crackling to have a salty flavour so we use a lot of flake salt on the surface. You may need to use a small amount of oil to help the salt adhere. Neither are necessary for crackling.

Salting Pork

Salting Pork

Salted Pork

Salted Pork

Step 2: Lighting the spit roaster

Light up a bag of heat beads and leave them until they are white hot. Spread them into a single layer of beads. This is important, too much heat and you won’t be able to control the s-curve you’re chasing and you’ll go straight to burned.

Lighting the Spit Roaster

Lighting the Spit Roaster

Ensure the coals are spread in a thin layer

Ensure the coals are spread in a thin layer. Stamp them down with a garden tool if need be.

Step 3: Start cooking in segments.

This is the only slightly tricky part of the process.

Start off cooking one segment at a time.

Start off cooking one segment at a time.

  1. Turn the rotisserie off. You will hear the pork start to make a sizzling sound as the fat is heated. Allow it to heat for a minute or so (you will have the judge the correct time based on the proximity of your rind to the coals and so the amount of heat it is receiving). Ensure it does not blacken. At this point you’re building the heat on the skin. You should not be aiming for crackling now, just heat the rind and see it dry out slightly.

  2. Turn the rotisserie motor on and allow the pork to do one 360 degree rotation and stop it back where it was in step one. At this point you’re allowing the sector of crackling you’re creating to cool just enough to avoid burning the surface.

  3. Allow the section of rind to heat. Again, you must watch it carefully. Repeat the process of exposing that sector of crackling to the coals with a ‘rest’ rotation.

  4. At some point you will notice the crackling form very quickly when you hear the surface of the rind make a small pop/fizz sound. It might take several rotations like this for the crackling to ‘pop’.

  5. At this point you are done with that section and need to rotate the rind to the next section that has no crackling and repeat.

You'll see crackling form in segments as you work your way around the meat.

You’ll see crackling form in segments as you work your way around the meat.

Once you've worked your way around you'll have created the Tunnel of Love.

Once you’ve worked your way around you’ll have created the Tunnel of Love.

More crackling

More crackling

 

Step 4: Cooking the pork itself

Once you have performed this across the entire surface of the rind, you should leave the rotisserie on for the rest of the cooking. The fat under the skin renders during the cooking process and bastes the surface in its own juices. This does not in any way soften the crackling.

Ensure you have meat thermometer in the centre of the pork and take it off when it indicates it is done (77 degrees celsius, 170 degrees fahrenheit). It is okay (and we think preferrable) to have the pork slightly pink in the middle so long as the liquid runs clear.

Pro tip: When the core of the meat is around 50-55 degrees celsius, put your roast veges on. They’ll finish at the same time as the meat.

Even more crackling

The meat itself will cook on autopilot provided you don’t have too much direct heat.

Step 5: Crackling and resting

Once the pork is off the heat, immediately cut the butchers twine and discard. The entire cylinder of crackling easily separates from the meat leaving you with a solid tube of crackling. We call this the tunnel of love. Use a desert spoon to scrape the excess gelatinous fat off the inside of the crackling and toss it in your gravy. The crackling can be left to stand on the bench. Do not cover it.

Take excess gelatinous fat off the outside of the meat and add it to your gravy. The meat should then be covered in foil and allowed to rest. We normally leave it rest for the time it takes to round up the guests, get the veges out of the oven and salted.

Remove the butcher's twine

Remove the butcher’s twine

Step 6: Carving the meat

The meat itself does not look very appealing with the cracking removed so presentation through carving is important.

Place the meat on a cutting board. Any juices from the meat resting should be poured into your gravy. The meat itself should be carved into medallions approximately 10mm (⅓ of an inch) thick and placed on a serving dish.

Step 7: Crackling and world peace

The butcher’s twine leaves heavy ring marks in the crackling. You can snap the crackling along these marks easily. Alternatively, you can cut it in halves with a cleaver and serve it in squares.

The beauty of the TwoPorkSwords method is that there is no fighting! It works so reliably you can produce crackling in abundance. Be careful though, with ultimate power comes ultimate responsibility. We once blew our pork fuses and couldn’t eat pork or crackling for a month.

When your four year old son looks at you with heavy eyes and says: “Dad, I’ve had enough crackling.” you know you have hit a parenting milestone.

About the author

David Connors is a consultant and software engineer working with a number of firms. He like pork.

5 Comments

  1. Sooo…. Ive wasted the last 4hrs of my life reading about all the fanciful ways of cooking pork correctly, when in 5 mins i had 99% the answers I needed.
    Roughly how many kgs is the one you cooked in the photos?
    And how long was it go to whoa ie: light the heat beads to off the shaft?
    Ill post some pics after the Christmas feast.
    Yours in porking
    Slackjaw(Cletus)

  2. Some nice protips there; will have to try.

    Thank you sir.

  3. Pingback: Use The Power Of Science To Make The Perfect Crackling Pork | Lifehacker Australia

  4. Fantastic! The best cooking article I have EVER read! Nice work David.

  5. Will be trying this for my next pork roast, haven’t been having much success with the crackling so far but this looks promising.

    Out of curiosity, would the same principles apply to crispy skin on poultry? I’m also working on my roast duck, with about as much success as my pork so far…

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