Why lobsters turn red when cooked

The reason why lobsters turn red during cooking is because of a fascinating combination of chemistry and quantum physics. Find out how in Curious Cook's first of a two-parter lobster tale.

It is fair to say that I work in an unforgiving industry - it's a business where one is expected to deal with terms like interpolation, heteroscedasticity, tolerance invariance, etc.

Sometimes I wonder why I do it but for my current stint, there's at least one very good reason - my workplace is practically next door to the best lobster house in London, if not the UK, a friendly unpretentious joint which I frequent at least twice a week.

It is really worth coming in to work just to have lunch or dinner here. And all my colleagues agree.

You would already know that raw live lobsters are not red in colour, though they are always red when they are served at the table.

When alive, lobsters range in colour from muddy dark olive to speckled grey - not hugely attractive colours which they adopt simply because they like to be camouflaged and remain unseen by predators on the sea bed.

The reason why lobsters turn red during cooking is because of a fascinating combination of chemistry and quantum physics. The story starts with a carotenoid called astaxanthin.

Carotenoids are organic pigments - for example, the orange colour of carrots is due to carotenoids.

Lobsters do not manufacture astaxanthin themselves - they get it from ingesting microalgae such as Haematococcus pluvialis.

Free astaxanthin is actually bright red in colour and the carapace and shell of the lobster's exoskeleton contains prodigious amounts of astaxanthin.

However, we don't see much of the default red colour of astaxanthin on living lobsters because the red compound has undergone either bathochromic or hypsochromic shifts due to the interaction with a protein called crustacyanin.

To re-phrase that, it means that the colour spectral band (the colours we see) of the astaxanthin molecules has been modified to a longer light wavelength (bathochromic) or a shorter light wavelength (hypsochromic) due to the protein crustacyanin.

How this chromic modification occurs is really curious - one might have assumed that crustacyanin just coats the astaxanthin and stops the red colour appearing. And to a certain degree, this does indeed happen but the whole story is much more intriguing.

If it was just crustacyanin coating the red astaxanthin molecules, then this would mean that the colour change of a cooked lobster would only be around 30 per cent of the dramatic colour transformation that we observe - it would be like wiping some dust off a car body to see more of the colour underneath, and the lobster itself would also appear much more red as well, even while it is alive.

But we know that live lobsters normally never ever exhibit much red colouration at all.

So the reason for most of the potency of the colour change is actually due to the quantum arrangement of astaxanthin itself when it is held inside a crustacyanin molecule.

The astaxanthin molecules are re-arranged into "X" formations within crustacyanin, a particular structure that serves to change their quantum energy states, altering the wave lengths of the light they would normally absorb, so that the lobster appears darker, more bluish, more greenish, or just more grey.

There are 16 protein chains of crustacyanin binding to 16 molecules of astaxanthin in a convoluted arrangement, so it is quite a complex configuration.

When heated, the crustacyanin proteins become chemically unstable and break up - allowing the bound astaxanthin molecules to untangle themselves and display its natural dramatic deep red colour.

Notwithstanding the colour changing aspect, lobsters are exceptional creatures in other respects.

For one, they can regenerate any part of their body that has broken off or is damaged - sometimes they even self-amputate parts of their bodies to escape danger.

They do not lose fertility with age and very old lobsters would appear to be actually more fertile than younger ones.

As with most arthropods, they have to moult as they grow in size. However, lobsters tend to overdo their moulting cycles - for example, even while inside the egg, a lobster larva will moult six times, and once hatched, they will moult another nine times within the next months, making 15 moults in the first year of life.

The moulting slows after the first year, only occurring four times the second year, and two to three times the next year until they moult only once every two to three years after the seventh year. They are ready for eating after about seven years.

Unlike some creatures, even the eyes of the lobster moult - talking of which, the retinas of lobster eyes are convex unlike most mammalian eyes which have concave retinas.

That's probably because they don't use their eyes much as they rely mostly on their long antennae for sensory perception.

They live a long time too, perhaps up to 100 years - but that's just an estimate as nobody knows for sure.

The earliest clawed lobster fossils date back to the Cretaceous Period, some 140 million years ago. They are from the Nephropidae family and have 10 limbs, of which six are extensions of the mouth.

For the food lobsters that we dine on, the first pair of limbs are enlarged pincers which we know as the claws but there are also smaller claws on the next two pairs of limbs which we seldom notice.

In Europe, the main lobster species we eat is Homarus gammarus but the ones I enjoy at the restaurant near work are Homarus americanus, shipped in fresh from North America daily.

The blood of lobsters is clear in colour though it turns blue when exposed to air - this is because their blood uses haemocyanin for its oxygen transport.

Haemocyanin is based on copper as opposed to the blood of most mammals which uses haemogoblin which is persistently red and based on iron. Lobster blood turns opaque white after cooking and has no discernible taste.

Talking of taste, gourmet diners have acknowledged that the tastiest lobsters are those which have just moulted. The new shells are still paper-thin and the meat is really very sweet and delicious.

Old lobsters have less meat, and are also often significantly less tasty - but ironically, the older and tougher the lobster, the higher the price.

This is because just-moulted soft lobsters are very difficult to transport without killing them, while lobsters with firm shells can be transported alive for longer distances and hence are more valuable to restaurants.

The older (and least tasty) lobsters which have not moulted for a year or more have even harder shells and can be transported and kept alive for even longer distances - hence they command the highest prices.

So the less tasty the lobster, the more expensive it is, purely because of the survivability rate. This is why one should perhaps avoid those lonely lobsters that you sometimes see in fancy tanks in swanky restaurants - the meal would be more about presentation and showing off the lobster than the flavour. And it will be expensive.

Regarding expensive restaurants, a friend had texted me to say that she had a terrible reaction after eating lobster at such a place.


While there are unquestionably people who are allergic to shellfish, the most common causes for such reactions in ordinary people are more to do with environmental contamination, food hygiene - and tomalley.

Lobsters and all other shellfish can suffer environmental contamination, particularly from toxic algae in the waters.

One such group of contaminant poisons is okadaic acid toxins (or OA-toxins) which causes rather nasty diarrhoeic shellfish poisoning.

So it is important to ensure that the source of lobsters come from good, safe regions. Due to the cost, many restaurants will serve lobsters that are not fresh; that is, lobsters that are dead on arrival. This is not a good idea at all.

The reason is that the inside body cavity of a lobster is filled with tomalley, which is the hepatopancreas of the arthropod - it turns into a dull, greenish paste when cooked.

Tomalley functions as both the liver and the pancreas, and as such, can accumulate significant amounts of toxins which they filter out from their environment - for example, they are particularly good at extracting and accumulating PCBs, stuff which you really don't want to ingest.

Tomalley also has another deleterious effect - as part of its pancreatic function, it is full of enzymes and once the lobster is dead, these enzymes gush out and set about digesting and destroying the protein structure of the lobster flesh, rendering it somewhat squishy in texture, like the inside of a rotten cucumber.

At the same time, bacteria and other toxins in the tomalley will also leach out and contaminate the rest of the carcass, giving rise to a slight ammonia odour.

So if the lobster meat you get in a restaurant is mushy or smells a little like bleach, refuse it at once. If you are unsure, you can also request that the tomalley be removed before the lobster is served as some restaurants still serve it inside the shell.

That is what I do myself - although the taste of tomalley is rather rich and flavoursome, I am less keen on the unwholesome extras that come with it.

One common fallacy is that cooking kills off all bacteria and toxins in food.

The truth is that while cooking temperatures will kill off almost all bacteria, many food toxins which have already been produced by the bacteria are heat-resistant chemicals and cooking does not impair their toxicity at all - OA-toxins are not at all affected by normal cooking heat, for example, though the heat will kill off all the algae that produce OA-toxins.

* The story of lobsters continues in the next Curious Cook column.