Why is my coconut milk blue?

September 24, 2006 12:19 AM

Why did my coconut milk turn blue?

I used half a can of organic, light coconut milk in a recipe and then forgot about the rest of it. Two weeks later, I unearthed it from the back of the fridge, and it was blue. Vibrant, eye-stinging, cobalt blue. Very pretty, actually. But why?

posted by changeling to Food & Drink (16 answers total)

Is there anything on the ingredients list except for coconut extract and water? That's a frightening colour for food and not one I'd expect to get from a reaction with the steel can.

Was there anything above it in the fridge that may have dripped in? Is it blue all the way through or just at the top?
posted by polyglot at 12:50 AM on September 24, 2006

It's obviously a bacterial or fungal growth.
posted by delmoi at 12:55 AM on September 24, 2006

Wow.

That's one hell of a blue.
posted by evariste at 1:57 AM on September 24, 2006

Wowzers.

Coconut milk contains a plant growth hormone that promotes cell division, and so is often used as a culture medium in experiments. So, apparently, that's not bad coconut milk - that's SCIENCE! Congratulations on your new.... um, whatever!
posted by taz at 3:14 AM on September 24, 2006

Yeah, I'd have to buy lab mice just to make them eat it. Are you sure this isn't coconut milk from a cracked meteor?
posted by adipocere at 5:00 AM on September 24, 2006

(In the remote case you're still thinking this coconut milk is salvageable, please don't eat it.)

Could it be blue mold? That's an airborne fruit-infecting spore which likes refrigeration.
posted by brownpau at 5:58 AM on September 24, 2006

You either have mold or children.

Children with food coloring.
posted by Wolfdog at 6:16 AM on September 24, 2006 [2 favorites]

"Open cans of coconut milk must be refrigerated, and are usually good for a few days. An open can should never be left at room temperature, as the milk can sour and spoil easily."

Whatever it is, no way it's still safe to consume.
posted by luftmensch at 6:42 AM on September 24, 2006

From the color I'd wager it's a proliferation of some kind of Penicillium fungus. It's a common, ubiquitous household mold, grows easily, and can form blue colonies.

(Various penicillin species are responsible for the fuzzy blue mold that hits fruit (as mentioned by brawnpau), for the blue mold that destroys tobacco crops, for the blue-green moldy color in roquefort cheese, another species is used in brie & camembert, and Fleming's famous p. notatum from which he isolated the antibiotic penicillin. That shit is everywhere--most people reading this could probably find some sort of penicillium in their kitchen right now.)
posted by neda at 7:42 AM on September 24, 2006

fwiw, I've had coconut milk go bad and turn blue (a much whiter color, though).
posted by maniactown at 8:21 AM on September 24, 2006

Response by poster: Good morning everyone!

When I finally poured it down the sink, it was as solid as yogurt, and the dazzling blue layer was just a sort of peel, maybe half an inch thick. I assumed it was mold. I did not taste it. Bleehhh.

Do you think it being organic had anything with it?
posted by changeling at 10:09 AM on September 24, 2006

The cream in coconut milk rises, so that would account for the thicker top layer - also, was it uncovered in the fridge? That could cause the top to dry out and thicken, and maybe get contaminated by some other... something dripping or floating around in your fridge.

Garlic contains a chemical which can turn blue under certain circumstances (cooking immature garlic in a copper pan or exposing it to acids, I think). I've never seen it happen, but apparently the shade of blue is quite drastic. Also, once in a while my dried cranberries turn bluish-gray around the edges. Possibly coconut milk shares a chemical compound with garlic or cranberries? I did a little poking around but could find no evidence of this, but at least it proves it's not unheard of for a non-blue food to turn crazy shades of blue, given the right situation.
posted by jessicapierce at 11:26 AM on September 24, 2006

I would consider disposing of any other unsealed food in the fridge and hosing down the inside of the fridge with antibacterial and antifungal agents. If it got in your coconut milk, it could've gotten into anything else.

Our atavistic primate brains tell us "blue food is very bad," and this is solid, instincutal advice.
posted by solid-one-love at 12:28 PM on September 24, 2006

Could it be copper sulphates leaching from the tin can?

Or perhaps ferricyanide (aka Prussian Blue). After all, coconuts are very high in potassium.

It's a shame you didn't save a small sample. If you don't have a microscope to look for microorganisms, you could have spiked a *tiny* amount of the blue stuff into fresh coconut milk (kept in a glass container) and see if it gets bluer over time (suggestive evidence of microbiological growth - if it doesn't get more blue, it's suggestive that it was a chemical reaction; no iron around, nothing to get reacted into a blue compound).
posted by porpoise at 12:36 PM on September 24, 2006

jessicapierce, your cranberries turn blueish gray on the edges due to a pigment found in cranberries called cyanidin. When the pH of the pigment gets higher, the color will turn from red to blue.
posted by catseatcheese at 4:17 PM on September 24, 2006

Too much miles davis?
posted by DenOfSizer at 11:57 AM on September 25, 2006