How to clean and cut a whole crab

Video how to clean crab

This is a visual tutorial explaining how to clean and cut a whole crab. I’m using a mud crab but the same process applies to any large crabs. This accompanies the Singapore Chilli Crab I published today, arguably one of the BEST crab recipes in the world!

Singapore Chilli Crab - Mud Crab
  • Freshly made Singapore Chilli Crab ready to be served
    Singapore Chilli Crab
  • Dipping mud crab claw into Singapore Chilli Crab sauce

How to clean and prepare a whole crab

A whole crab – especially a live one – is not the sort of thing I cook with every day! So if your reaction to a crab is something like mine below, you’re in the right place. I’m going to walk you through step by step how to clean and prepare a whole crab, then show you how to make one of the most iconic crab dishes in the world, Singapore Chilli Crab!

It’s easier than you think. Trust me, you’ve got this!

Nagi live mud crab How to clean and cut a whole crab

After cleaning and cutting a crab

Once the crab is cut up, you will end up with:

  1. Crab pieces; and

  2. Crab juice plus tomalley which is also affectionately known as “crab mustard”. It’s actually the liver and pancreas of the crab, and this stuff is crab gold! It is packed full of crab flavour and, no self respecting foodie would ever create a crab recipe that doesn’t make use of it. It’s a secret ingredient in Singapore Chilli Crab that gives the sauce a massive savoury boost!

  • Cleaning and preparing crab 12 How to clean and cut a whole crab
    Crab pieces
  • Tomalley
    Reserved crab tomalley “crab mustard”

1. Buying and storing a live crab

1.1 Buying a crab

Nothing beats the fresh, sweet juiciness of a live crab! Here in Sydney, live crabs can be bought at the Sydney Fish Markets and some of the better, larger seafood shops.

  • Mud Crab at Sydney Fish Markets
  • Mud Crab at Sydney Fish Markets

The claws of large live crabs are strong and dangerous, so crabs will always come with their claws tied. Even so, always hold it from behind or by the top shell to keep your fingers clear of those nippers. If you’re still nervous about handling them while alive – and I don’t blame you – use sturdy tongs!

Raw mud crab

1.2 Storing a crab

For the juiciest, freshest and most flavourful crab, keep it alive until just before cooking.

If you’re cooking the crab the same day, simply leave it in a box or bucket in the open air. If you need to store it overnight, place the live crab in the fridge. The coolness of the fridge will subdue the crab, keeping it alive but in a physically depressed state.

Freezing and then thawing a live crab isn’t recommended – it defeats the whole purpose of a live crab! There’s also a noticeable loss of flavour and juice.

2. Dispatching a live crab

Dispatching a live crab is an unfortunate but necessary business. Doing it in a humane way will ensure the creature does not suffer.

2.1 How to humanely kill a crab

There are a couple of ways to humanely kill a crab for consumption:

  1. Spiking – This involves stabbing a knife or other sharp object into the brain and nerve centres of the crab. There’s one near the eyes and another near the tail. When done correctly, this kills the crab immediately.

  2. Freezing – The cold of a freezer puts the crab in a physically depressed, coma-like state so it feels nothing when you butcher it. This is the method I use, covered below.

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Putting mud crab in freezer to kill it humanely

2.2 How to dispatch a crab by freezing it

Place the live crab in the freezer until it completely stops moving but before the crab starts to freeze. This takes about 1 hour for a 1.5kg / 3lb crab. Don’t leave it longer or it will eventually freeze and die, which degrades the flesh and defeats the purpose of buying live crab!

Ensure that the eyes and limbs are no longer moving, it’s not bubbling around the mouth (breathing) and the legs hang limp.

At this stage, the crab will still be alive but is in a numbed, coma-like state of torpor. It is physically inactive and no longer feels any sensation. This occurs in crabs at temperatures of 4°C / 39°F or lower. Once it’s in this state, start preparing the crab immediately.

Watch how to do this step

3. How to clean and prepare crab

In this section, I’m sharing how to break down a crab for use in Singapore Chilli Crab. However, crab pieces prepared this way are suitable for use in any dish where crab is served in pieces in the shell.

3.1 Preparation and equipment

You will need:

  • A large cutting board

  • Kitchen scissors

  • A Chinese butcher’s knife, cleaver or very heavy duty kitchen knife

  • Three bowls – for edible crab pieces, reserving crab “mustard”, and a rubbish bowl

  • Wet cloths and tea towels

3.2 Remove sharp tips of legs

Place the crab you put to sleep in the freezer on the cutting board. Use scissors to cut off the sharp tip off each leg and discard. It’s best to get this out of the way first so you don’t poke yourself with them when handling the crab!

Cleaning and preparing crab template 1 How to clean and cut a whole crab

Watch how to do this step

3.3 Remove belly flap

Next, turn the crab over and remove the flap on the underside of the crab so we can remove the top shell. Lift up the flap and twist it off (discard).

Cleaning and preparing crab template 2 How to clean and cut a whole crab

Watch how to do this step

3.4 Remove top shell (carapace)

Next remove the top shell, called the carapace. Do this from the back of the crab, as indicated by the arrow in step 1 below. Stick your thumb under the shell, pull it up and off.

It’s usually easy but on occasion it just won’t budge! In this case, run a small knife down each side of the top shell then remove the top shell.

Cleaning and preparing crab 3 How to clean and cut a whole crab

Watch how to do this step

3.5 Reserve tomalley (crab “mustard”) from top shell

Inside the top shell you will see a funky-looking grey membrane and a yellow-green (or brown) substance. The grey stuff is of no interest to us, but the yellow stuff is gold! It’s called tomalley and it’s actually the crab’s liver and pancreas. Affectionately known as crab “mustard” or “crab fat”, it’s packed with intense crab flavour and is not to be wasted! It is a key ingredient in the magic sauce for Singapore Chilli Crab.

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To reserve the tomalley, scrape everything inside the top shell into a new bowl (let’s call this the Tomalley Bowl, we’ll add more to it later). Later we’ll sift through and sort out the good stuff (the tomalley) from the dud stuff (the grey and white stuff which is inedible membrane, guts etc).

Cleaning and preparing crab 4 How to clean and cut a whole crab

Reserve the now-empty top shell. We’re going to use it for decorative purposes in the finished Singapore Chilli Crab dish. Put this in a big bowl into which we will put all the crab meat pieces. Let’s call this the Crab Bowl!

Reserve crab top shell How to clean and cut a whole crab

Watch how to do this step

3.6 Reserve tomalley from crab body

Now we turn our attention to the crab body. First we’ll reserve the tomalley found here too. Use your fingers (or a teaspoon if you’re squeamish) to pull out all the tomalley and any attached grey tissue from the inside of the crab’s body. Add it all into the Tomalley Bowl.

Cleaning and preparing crab 6 How to clean and cut a whole crab

As with the top shell, there’s no need to be meticulous here. You can see above in step 2 that there is some tomalley stuck on the body cavity, and that’s fine. It’s going to make that body piece even tastier!

Watch how to do this step

3.7 Remove mandibles

Next, remove the mandibles, part of the crab’s mouth that’s marked in the photo below. Simple grab each one and twist them off. Discard.

Cleaning and preparing crab 7 How to clean and cut a whole crab

Watch how to do this step

3.8 Remove gills

The gills are inside the body and easily identified thanks to their other name, “dead man’s fingers”. They are not edible so need to be removed. They come off easily, just tear them off with your hands.

Cleaning and preparing crab 8 How to clean and cut a whole crab

Watch how to do this step

3.9 Cut off crab claws

This is the step that calls for a cleaver or heavy duty knife! Hack the crab’s arms off at the point where the arms meet the body. Bring the cleaver down on that point in one motion (watch your fingers!), letting the weight of the cleaver do the work.

Cleaning and preparing crab 9 How to clean and cut a whole crab

Watch how to do this step

3.10 Crack claws

Now we’re going to partially crack the shell of the claws. This serves 2 purposes: firstly to let some heat in so the claw cooks more evenly. And secondly to make the crab meat easier to remove. Be careful not to crack the claw fully open, otherwise the meat might fall out when cooking and break up in the dish.

To crack the shell of the crab claws, use a solid, general-purpose kitchen knife (like a chef’s knife). Lay the claw flat, and using the back of the knife (not the blade), smack the middle of the claw firmly until it cracks. Make one crack on each side of the claw.

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Cleaning and preparing crab 10a How to clean and cut a whole crab

Now using the cleaver again, cut each claw off at the joint. Add the claws and arm pieces to the Crab Bowl.

Cleaning and preparing crab 10c How to clean and cut a whole crab

Watch how to do this step

3.11 Cut crab body into pieces

The crab body should be cut into 4 or 6 pieces, depending on how large the crab is. For a large crab around 1.75kg / 3.5lb, I would cut the body into 6 pieces (two halves, each cut into three). For a smaller 1.25kg / 2.5lb crab, cut the body into 4 pieces.

Using the cleaver, cut the body in half down the middle (step 2 below). Stand one half on its side and cut down through it, so you have two pieces each with legs attached. Repeat with the other half. (Cutting the body up is easy as the shell is quite soft.) Add the crab pieces to the Crab Bowl.

Cleaning and preparing crab 11b How to clean and cut a whole crab

Watch how to do this step

3.12 Crab pieces, done!

And with that, you’ve got your beautiful crab pieces! Before you start cooking though, we need to deal with the tomalley. No self-respecting foodie would ever create a crab recipe that didn’t make use of the tomalley. It’s a built-in booster of free crab flavour!

Cleaning and preparing crab 12a How to clean and cut a whole crab

Watch how to do this step

3.13 Cleaning the crab tomalley (crab “mustard”)

Scrape all the crab juices that have collected on the cutting board into the Tomalley Bowl – more free crab flavour!

Cleaning and preparing crab 12b How to clean and cut a whole crab

Pick up a piece of membrane (the grey or white lining-like bits) and use your fingers to scrape the yellow and green “paste” off back into the bowl. (OK fine, slime is a better description!)

Cleaning and preparing crab 12d How to clean and cut a whole crab

Discard the membrane. Continue until you’ve picked out all the membrane and you’re left with the yellow and green crab “mustard” in crab juice.

Cleaning and preparing crab 12c How to clean and cut a whole crab

This bowl of completely unappetising-looking goo is worth its weight in flavour gold. Think of it as liquid crab concentrate, supercharging with crab flavour anything it’s added to, like the sauce of Singapore Chilli Crab (the recipe today’s crab is for).

Singapore Chilli Crab 0 How to clean and cut a whole crab

Watch how to do this step

3.14 Cooking the crab

Tomalley ready to go, crab pieces prepared … congratulations! You just successfully broke down a whole crab! Give yourself a pat on the back. Pour yourself a wine and have a well-earned break. While you sip, let your mind wander to the delicious things this crab is about to be transformed into.

Because now it’s time to cook this beauty!! (Like the Singapore Chilli Crab recipe, right here 😇) – Nagi x

  • Close up photo of Singapore Chilli Crab
  • Dipping mud crab claw into Singapore Chilli Crab sauce

Watch how to make it

Life of Dozer

Dozer’s reaction to a live mud crab vs mine. 😂

But I couldn’t let Dozer show me up! So I gave the giant wriggly mud crab a kiss! 😂

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Ethan Smith is a seasoned marine veteran, professional blogger, witty and edgy writer, and an avid hunter. He spent a great deal of his childhood years around the Apache-Sitgreaves National Forest in Arizona. Watching active hunters practise their craft initiated him into the world of hunting and rubrics of outdoor life. He also honed his writing skills by sharing his outdoor experiences with fellow schoolmates through their high school’s magazine. Further along the way, the US Marine Corps got wind of his excellent combination of skills and sought to put them into good use by employing him as a combat correspondent. He now shares his income from this prestigious job with his wife and one kid. Read more >>