It's an indication that the fruit has started to rot: When dark spots start appearing on the side of a mango, it's starting to rot.
A mango can rot from the pit, the skin, or from the non-stem end.
Any black fibers also indicate that the fruit has started to rot, and at that point, you need to toss it into the trash.
From: Student's Vegetarian Cookbook For Dummies, page 301 Edit
: Yes, the above is probably being overcautious in stating “ any black fibers?
→ trash!”
It's from a “Dummies” book after all.
;) I couldn't really find another good reference.
But I'm sure you can make the distinction between a piece of fruit that has a small brown spot and one that's black and shriveled.
Still, the color of the fibers is a result of the late ripening/rotting process of the mango, rather than a result of an earlier stage in its growth.
But having eaten this mango with the one, tiny black fiber shown in her picture, I don't really expect to read Mien's obituary on this site tomorrow.
;)
cooking.stackexchange.com/users/4012/Rinzwind
Black streaks in mango.
Please read the following articles from www.abc.net.au: Mango industry baffled by mystery disorder Mystery mango disease not so mysterious These articles identify the presence of well delineated black veins in otherwise good, fresh mango as a "disease" of the fruit.
It turns out that this is caused by the mango trees lacking sufficient fertilizer.
cooking.stackexchange.com/users/25548/John
I believe some mangos do that in early stages of over-ripening (similar to how an avocado does that).
I usually cut around them and keep eating.
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It's not mango rot its actually a disease called Resin Canal which causes black fibers to appear in mangoes, there is no idea what causes the problem
cooking.stackexchange.com/users/73639/Raimond Bin
Mango industry discovers highly infectious bacteria as cause of ugly veins of resin canal discolouration https://www.abc.net.au/news/rural/2019-03-19/resin-canal-discolouration-breakthrough-for-mango-industry/10912520
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Just to keep this thread accurate and current, the black fibers/veins in the picture are known as Resin Canal Disease, or RCD.
Although unappealing, they are safe to eat, as described in this article: https://www.abc.net.au/news/rural/2019-03-19/resin-canal-discolouration-breakthrough-for-mango-industry/10912520
cooking.stackexchange.com/users/85140/Researched in 2020
I was cutting up a mango, when I noticed some black threads inside.  What are those?   They are quite tough, brown-black, about an inch long (2.5 cm):
What are those black fibers in my mango?
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<mango>
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This could be a sign that the mango is starting to rot, or has a disease called Resin Canal which causes black fibers to appear in mangoes. This can be caused by the fruit starting to rot or a disease in the fruit.
This is an indication that the fruit is starting to rot. This is caused by a disease in the fruit.