7

Freshly bought carrots turn black (like coal) on peeled surfaces in minutes if not seconds. I wonder why and why are these special. Obviously it is not black rot. The carrots taste normal, albeit not too sweet. Too much fertilizer nitrates? Or just contain lots of starch like in potatoes? The carrots were clean to begin with and I washed my hands too :-) peeled carrots turning black

Update: I live in Denmark and these carrots are from Spain, perhaps Canary Islands, fresh veges seem like a bit of a struggle here, hence I am surprised.

  • 1
    Anything notable about the tool used to peel the carrots? – PoloHoleSet Dec 29 '17 at 17:59
  • @PoloHoleSet just ordinary knife – MariusM Dec 29 '17 at 18:01
  • What type? Stainless steel? Carbon steel? Ceramic? – Catija Dec 30 '17 at 4:03
  • @Catija stainless steel – MariusM Dec 30 '17 at 11:00
7

I must admit that my answer contains a bit of speculation.

Let me start with beta carotene which is the pigment responsible for the orange colour of common carrots. It is easily and quickly oxidised by exposure to air and enzymes already present that get activated upon cutting and exposure to light. As such it looses its orange colour very quickly.

Now, browning of fruits and vegetables happens for oxidative processes when they are exposed to air. It is a common an unpleasant occurrence.

Where I do speculate a bit is on why the browning is so pronounced in the case of carrots to be even described as "blacking".

I have few possible reasons that make sense to me (consider I have to deal with "colours" at work, if this gives a bit of credibility).

  1. Carrots are deep orange. The dark layer of oxidised surface on the underlying orange gives us a almost black colour.

  2. Carrots contains other deeply coloured pigments. Some are darker than beta carotene (indeed carrots originally came in purple, and some are indeed black!) and more resistant to oxidation. As such oxidation of beta carotene can reveal darker pigments (anthocyanines) otherwise unnoticed.

    This is somehow similar to what happens with leaves. At first they are green due to their content of chlorophyll. Once they fall, chlorophyll has been degraded and other red and yellow pigments become visible.

  3. A mix of the above, depending on the type and amount of pigment present in that particular carrot.


Extra: if cooking with carrots they get a green tint, this is due to a too high (alkaline) pH. For instance too much baking soda in the batter. Pigments can be sensitive to pH, too.

Based on the comment of Lorel C. Indeed the level of tissue damaged as well as porosity are know to exacerbate the browing process.

https://www.ncbi.nlm.nih.gov/m/pubmed/10971842/

This is evident when instead of sharply peeling the carrots we clean them by scratching with a blade hold perpendicular to the surface. This is likely to be the case depicted in the photograph by OP.

Many recipes indeed recommend the use of soft brushes to clean carrots.

  • 1
    Carrots are purple. In the S.Pacific. Medical plant. In west China carrots are yellow. A medical plant. A cross breed of the 2 gives you today the eating carrot at the store. Orange. – J Bergen Dec 29 '17 at 4:46
  • 1
    @J Bergen. Right. Yellow and purple are the original ones. Some are so dark purple to be referred to as bkack. – Alchimista Dec 29 '17 at 8:25
  • Oxidation of carotenoids does seem most likely. Haven't seen it here in the States, but we've probably all been eating clones of the same carrot for 25 years. Spanish carrots, who knows? – Wayfaring Stranger Feb 13 at 0:33
5

This looks to me like simple oxidation. It is just that your batch shows it more than others.

It is completely normal for plants of the same species to have very different amounts of the same chemical compound. Think of capsaicin in peppers, which vary from sweet to your-intestines-will-be-on-fire-for-days, anthocyanins in tulips (or carrots) which can have none (whitish) to be chock full of them (dark purple), or the aroma compounds which are concentrated in oil roses and absent in the roses bred for the grocery store shelves.

Oxidation browning occurs when oxygen from the air activates an enzyme in the fruit (or vegetable) which then reacts with phenolic compounds in the plant tissue. You must have happened upon a batch of carrots which has high amounts of phenolics, or an unusually efficient enzyme, or large amounts of the enzyme.

  • 3
    From your picture,it looks like you scraped the outer surface off the carrots rather than peeling them (with a sharp blade). Mine do that too when I scrape them - not so extremely dark as yours, more a grayish brown. But I just figure since they get so rough from the scraping, there is a lot of exposed surface area for oxidation, more than the smooth surface from a knife or peeler. – Lorel C. Dec 29 '17 at 17:44
  • Not sure phenols are involved in carrots. Otherwise good answer too. – Alchimista Dec 30 '17 at 9:48
  • @Lorel C. I will add few lines to my answer based on your comment. – Alchimista Dec 30 '17 at 9:51
-5

To me it looks like black fungus. If these carrots were picked right after the typhoon. Washed in a bleach solution. Then stored. They would look good at the store. Once peeled the fungus could be there. Then show very fast. This is just a guess may not be.

  • As I understand fungus grow within days, but in my case the first carrots turn black while I peel the second, it's like my hands were in soil without soil :-) – MariusM Dec 29 '17 at 10:47
  • You do not live in the tropics. After a long rain or typhoon. Black mold can set in. On root crops very fast. So you wash them to remove. Store cool & dry. Once removed from storage peeled the fungus root is still there below the skin. Warm & moist. It can spout very fast. Or root crops after a storm can be washed in vinegar. To kill the surface mold or fungus. Leaving a light acid coat on the skin. But this is a guess. I would need a microscope to know for sure. – J Bergen Dec 29 '17 at 14:46
  • 1
    This is such a common discoloration. Bringing in fungus, typhoons and bleach is an amazing stretch that would leave Occam baffled. – Willem van Rumpt Dec 29 '17 at 15:46
  • @WillemvanRumpt - since OP did not specify a geography, I prefer to think of it as just being especially thorough and open to possibilities. I would be surprised if this were the cause, though. – PoloHoleSet Dec 29 '17 at 18:01

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