Why beets turn black – the mystery continues

Also Read: How to Roast Beets – No Foil, How to Boil & Freeze Beets, How to Pickle & Can Beets

Why do beets turn black?

My first occurrence of this was in August of 2014, that’s when I wrote the following post. Since then, I’ve received feedback and comments from readers who have experienced black beets after preparing them in various ways – boiling, roasting, with or without aluminum, it doesn’t seem to matter. To this date, I do not have a definitive answer.

My latest theory is that maybe the blackening of beets is similar to blackening of boiled potatoes or After-cooking darkening – a widespread issue across the world and of great concern to commercial potato processors. Here’s what the American Journal of Potato Research has to say about it:

After-cooking darkening (ACD) is one of the most widespread, undesirable characteristics of cultivated potato. After-cooking darkening is caused by the oxidation of the ferri-chlorogenic acid in the boiled or fried potatoes.

The Idaho Potato Growers add this

If the potatoes were stored too cold (below 40 degrees F) then they can turn black. They could also have black bruising from being handled (dropped) when cold. If your potatoes turn black after they are boiled, you may be using an aluminum or reactive pot, so it’s important to use a pot that’s non-reactive.

While cooling, iron in the potato combines with other natural compounds, causing a grey, black, or bluish purple color. To prevent this, after the potatoes are cooked and drained, stir in a small amount of lemon juice and keep them covered with a tight-fitting lid.

Are potatoes and beets similar in this way?

I don’t know. But after repeated efforts, I’ve decided on the following processes:

  • avoid putting fresh beets in fridge if possible
  • leave skin on when roasting or boiling
  • avoid using aluminum foil when cooking beets

Wishing you all beautiful black free beets!

….

Here’s what I wrote in 2014:

I was so excited to harvest these red and gold beets from my garden.  It’s the first year that I grew golden beets and I was excited to cook up my first batch.  Look how gorgeous these guys are!

red and golden beets
amazing beet color
roasting beets

Normally, I boil my beets, peel ’em then dice ’em.  But I wanted to treat these beauties special, so I looked up an Ina Garten recipe for roasted beets.  It said to peel and dice the beets, so I did.

When I pulled them out of the oven, I was disappointed.  The beets looked dirty with a few black spots and an all over look of gray.  The beautiful color was gone, I didn’t even take a picture because they were really not photo worthy.  We ate some and they still tasted good, but they weren’t pretty or special. I put the leftovers in the fridge. Here’s what those leftovers looked like the next morning – CAUTION these images may be upsetting to some readers!

black golden beets
beets turn black

The black dirty look had intensified.  It looked horrid.  Even the red beets turned black, it was just more difficult to see. What happened?  The flavor wasn’t affected (yes, we tried them), just the color.

I scoured the internet looking for answers – was it just me, was it my beets, was it the recipe??  What?

Google came up with tons of results to my query, but it did not provide the straight forward answer I was looking for.  There were lots of discussion threads about similar occurrences and quests for answers like mine – but no conclusive answers. At least it wasn’t just me or my beets.

People had lots of guesses: beet variety, oxidization, the sugar/starch in beets, too much manganese in the soil, a reaction to aluminum foil, peeling them before roasting, the beets were picked too early, need to soak them in lemon juice, etc.

I didn’t find anything conclusive, so I thought about what I did differently this time than the gazillion other times I’ve cooked red beets and did not experience this issue. This was the only time I peeled the beets before cooking and I roasted them on aluminum foil.

beets

Last night I harvested more golden and red beets, determined to do better. I cooked them right away, ie. they didn’t spend any time in the fridge. I made them the way I normally cook beets.  I washed the soil off, cut off the greens and tossed the whole beets in a pot of water where I boiled them until they were fork tender (20-40 minutes depending on size).  I took them out of the hot water, rinsed them in cold water, allowed them to cool, peeled and diced them.  Here’s what they looked like:

red beets boiled
yellow beets

Beautiful and photo worthy!  Not a spot of black.

red and yellow beets boiled
red and gold beets boiled

I put the leftovers in the fridge – the next day they still looked beautiful.

What was different?

  • no aluminum foil
  • no refrigeration of beets before cooking
  • boiled instead of roasted
  • different batch of beets but same soil and growing conditions

Which of these factors is making the difference? I can’t say for sure.

Here’s my plan moving forward.

  • avoid putting fresh beets in fridge if possible
  • leave skin on when roasting or boiling
  • avoid using aluminum foil when cooking beets
apple and beet salad

Now I can make Apple and Beet salad or Beet and Feta Salad.

Have you ever had your beets turn black?  Do you know the scientific explanation – please tell us!

Getty Stewart is an engaging speaker and writer providing tasty recipes, time-saving tips, and helpful kitchen ideas to make home cooking easy and enjoyable. She is a Professional Home Economist, author of Manitoba’s best-selling Prairie Fruit Cookbook, Founder of Fruit Share, mom and veggie gardener.

58 Comments

  1. Glad to have found this blog. I just roasted a roaster of yellow beets to freeze and, sure enough, they turned black/grey. So did my hands when slicing the raw beets. I’m guessing it’s oxidation. We’ll be eating them anyay, just not for company.

    Last year I didn’t have many yellow beets, so just boiled them in their skins for each meal, and peeled and froze some left over cooked ones. These were ok. I’m not going to roast them next year. By the way, I always boil and pickle red beets, and they always turn out just fine.

    Will visit this site next fall before doing anything with the tasty yellow beets.

    1. Thanks for sharing your experience Sandra. Maybe it’s just so much more noticeable with the yellow beets.
      All the best,
      Getty

  2. Hi, at my work we had a very similar situation. We peeled and diced the beets for our upcoming Thanksgiving dinner and because of the volume of beets we needed, we had then peeled a couple days in advance. Nothing happened to them as they sat in the cooler waiting to be cooked. We par steamed them as our plan was to roast them the next day for service. When we checked on them the following morning they were all black, the yellow and the red. So disappointing.

    After reading your story, it must be something to do with taking the skin off and exposing them to the air and once it’s cooked, that is when it alters the appearance.

    We are serving them once again for this Thanksgiving dinner so hoping that we can figure out a different method so that this will not happen again.

      1. Aluminum foil is the culprit if the beets have been peeled/cut. I just tried to make a pilaf in the oven with grated beets and dill. To seal the pyrex lid better I thought I’d try a layer of foil between the lid and the dish. Oh my goodness! When I took it out, the entire top layer had gone from beautiful deep purple to a disgusting totally black colour. It was lovely underneath so I mixed it up and it tastes great but holy cow was that a frightening unveiling of a new dish. Yuck!

        1. It’s so frustrating! You start with such beautiful vegetables and have them ruined! It still baffles me because I have had this happen even when not using aluminum foil.

  3. Hello Getty,
    I canned my Detroit Dark Red beets from this past spring in pint jars, in a pressure canner. Just 1/2 tsp salt, and water (I do carrots the same way). Boiled them, peeled the skins off, and sliced into bite sized chunks. Pressure cooked them at 12-13 lbs pressure for thirty minutes. They were simply cooled to room temp and stored under my stairs in the basement (no refridgeration). They have black spots, and some of the concentric rings are black alternating with the dark red of the beet. My wife and I were terrified of botulism, but all of the jars have this issue, so it’s not an issue of not having a good seal. I got brave and ate a few, and have not suffered any ill effects. They taste like beets should, the color just looks absolutely horrible. I was hoping someone at our county extension office could offer an explanation.
    -Wichita, KS

    1. Oh no, how very disappointing. I hope your extension office can provide some information to help avoid blackness in the future.

      Your canning method sounds right on track for safe pressure canning of beets according to the National Centre for Home Food Preservation http://nchfp.uga.edu/how/can_04/beets.html.

      Just remember if Clostridium Botulinum is present in a jar, you will not be able to taste, smell or see it. It thrives in low acid, low oxygen and moist environments.

      Gosh, I sure wish we all had an answer to this!
      Getty

  4. Good to know I’m not alone. I washed, partially pared the skin and roasted in olive oil with a little garlic. Upon removing them from the oven, black spots. Today more black sots. No aluminum foil. Pretty upsetting as I have done this many times and never had this happen. I, like many of you stumbled on this site looking for the cause. Oh well. I love beets and do not like wasting money.

    1. I haven’t had black beets for a long time now – roasted or boiled. I try to avoid letting them get too cold or stored to long in the fridge – just in case the culprit is prolonged storage at too low temps.

  5. I was so glad to read this. I was horrified after my beautiful roasted beets were black this morning. I threw them away, then came across this article. Thank you for this article and your blog.

    1. There is some comfort in knowing it’s a thing that sometimes happens with beets and it’s not you! Glad the article provided some comfort even if there isn’t a definitive answer yet.

      1. That is a good question. I would pose it an expert like Alton Brown if I had the chance to speak with him.

        As of recent, I have been obsessing over beats and eating them practically everyday and I have been wondering that very same thing. I have found some storage tips that you may find useful too.

        A note on oxidation: Beets turn brown when they start to oxidize. The skin is a protective layer and once that is removed, or once the beet is sliced, oxidation begins. To minimize this effect, immediately put sliced beets into water, removing their contact with the air, or if eating them raw slice them right before you eat. This effect is purely cosmetic, they will still taste delicious even if they do brown slightly.

        Thank you for posting your blog I found it while I was searching for the answers and I’m happy to share this with you all.

        Buy local and be well.

        1. Thanks for commenting, Greg. I appreciate your thoughts and information.

          I’m about to harvest a nice crop of golden and red beets. Looking forward to some delicious raw and cooked beets in the next little while. I’ll also be freezing some for the winter.

          All the best,
          Getty

  6. Thank you for this. I roasted and froze my yellow beetroot only to find they’d started to turn black. I was worried about the rest of the vegetables, but now I know why the beets turned bad. I’ll be more careful with my next harvest, thanks again.

  7. I cooked a pair of beets for the same amount of time, one was smaller than the other and cooked more thoroughly whereas the larger one remained hard and relatively uncooked in the center. They were both golden when I peeled them after roasting in aluminum foil, then refrigerated for a day. The well cooked one looked great, including within the same tupperware stored with the undercooked one, which turned black only in the centers. This lends me to believe it is all a matter of how well the beets are roasted!

  8. We canned beets in summer 2016 all off them boiled with skins on. Some of the beets turned black and others arecstill red like usual. All of these were pickled and canned in the same process. Are they safe to eat?

    1. Oh Deborah, how disappointing that must be! I can appreciate how much time, energy and heart goes into every can of homemade goods!

      In this case, because we don’t know exactly what’s causing the darkening I would rely on the old adage – “if in doubt, throw it out”. I know that’s not what you wanted to hear, but it’s what I would do – and I really, really don’t like throwing away food!

      Based on what I’ve read, beets that turn dark after cooking are safe to eat – just like potatoes that suffer “after cooking darkening” are safe to eat. But with the added element of canning, it makes me a little more leery. You would think the acid in the pickling brine might actually prevent the darkening?! Too many unknowns.

      Do you remember if all the beets were harvested and stored in the same way at the same time? I wonder if some of them were stored too cool for too long (ie in the fridge for a couple of weeks) if they would be more prone to darkening? Just a thought.

      Wish I could offer more concrete information.

      All the best,

      Getty

  9. I have experienced this a few times. Roasted on a sheet pan, peeled, unpeeled, etc. they’ve turned black! I shredded raw golden beets and chioga beets and immediately saw them start to grey. I promptly filled the container with water to stop oxidation and they stopped but stayed gray. Tossed into lemon tahini dressing and hoped it wasn’t too bad but then I couldn’t bring myself to serve it grey! Tossed straight into trash before Christmas dinner!!!!

  10. I came across your post while looking for the answer to the same dilemma. I roasted golden beets in the oven, but not directly on the aluminum foil. I lined a cookie sheet with the foil but then placed rack over the foil. Then I washed and quartered the beets leaving the skins on and put them in the oven. The next day I took them out of the refrigerator and they were black – skins and all. The taste was fine, but they looked awful – like they had oxidized. I think I will try boiling them next time. Thank you for your post.

    Marianne

  11. I boiled my golden beats until they were tender than cooled them off in a bowl of cold water.. that’s also help the skin to peel off easier. I’ve been doing my beets like this the last few times but this time the next day when I took them out if the fridge the had black in half of all the pieces. .. I thought that was a bit creepy lol.. and I was bummed since I was excited to have them in my salad along side of my salmon for dinner.. Anyway.. so I’ve actually never roasted them in the oven yet with aluminum foil. So it must be getting it just rightb (who lnows) at the right tenderness maybe so it doesn’t blacken in the fridge. This time they weren’t as tender as they usually are… but so weird.

    1. Hi Lizzie,
      Thanks for sharing your experience. Based on the various reports, I believe that roasting or boiling, in or out of aluminum has nothing to do with it. My latest theory is that some beets, if stored too cool (ie. in the fridge) they’ll turn black – just like potatoes. I have an email in to a crop specialist with Manitoba Agriculture to see what he thinks of this theory.

  12. It’s not the cooking! I recently shredded some golden beets to use as salad prep for the next day and noticed portions of them turning a greyish black color. The next day, all were this color. They do not smell, feel or taste different, but I was concerned on if the quality had been compromised. Seeing as how it happened so quickly, and nothing else appears to be off about them, I have to assume it is related to the air and some sort of oxidation reaction.

    1. Thanks Julie Ann. Yes, I’m starting to suspect it may be similar to some potatoes turning black/gray and others not. Thanks for sharing your experience – as disappointing as it likely was.

  13. I work in fine dining and have to cook beets every other day (red and gold). I cut off both ends, sprinkle with kosher salt and pepper, wrap the beet completely in foil and place them on a sheet pan, cook in the oven for an hour and a half to two hours (depending on size), unwrap them to let them cool and then cut. I never peel them before cooking and I never get black spots. I hope this helps.
    Also, never leave them wrapped in foil sitting out for too long. They are a root vegetable and that can cause botulism.

  14. I work in fine dining and have to cook beets every other day (red and gold). I cut off both ends, sprinkle with kosher salt and pepper, wrap the beet completely in foil and place them on a sheet pan, cook in the oven for an hour and a half to two hours (depending on size), unwrap them to let them cool and then cut. I never peel them before cooking. I hope this helps.

  15. FYI I just quartered & steamed some beets (chioggia & a couple yellow, they were a bit soft from age, not firm & fresh) in a smallish stainless steel pan & they blackened really bad, so it didn’t have anything to do with aluminum; something about steaming versus boiling…

  16. For the first time ever, I roasted my beets with the skin on as usual but on an aluminum sheet and experience the black marks once they cooled and were refrigerated. I usually use stoneware with the skins on and roast my beets. I think the aluminum is the common element in all these posts, no pun intended.

  17. I roast my beets (red and yellow) with peel on and roast in dish on bed of rock salt. I peel them when they come out of oven, I have also let them cool then peel. But my beets get black spots too. You’re right about no one on the net having a definitive answer! I have tossed them in olive oil and/or fresh squeezed citrus…still get spots!

    1. Frustrating isn’t it! Someone commented that undercooking/roasting the beets might cause the issue? I have been roasting and boiling yellow and red beets with the skin on all this summer and have not had the dark spots return. Go figure.

  18. a slow saute in butter resulted in the same state. ANY TIME I have par cooked them I get the same result. I think the cure is to cook them thoroughly in the skins before exposing them to the air.
    Thank you Getty…

    1. Hmm, interesting thought Harvey, maybe I didn’t cook/bake them long enough? I’ve been baking them and boiling them with skin on ever since this incident and have not had a repeat of black beets.

  19. I’m not sure about the turning black, but I have a golden beet that has these like blackish ‘fibers’ running through it where the darker ‘rings’ are in the beet. It’s strange since I haven’t seen one like that before. I was trying to figure out if I should eat it or not. I decided to discard it since I don’t know what it is, it could me mold of some sort maybe I thought.

  20. I came across your website searching for the answer to the black beet question. FWIW, I roasted my golden beets with the skin on and placed them directly on the oven rack. So, no tin foil. The search for an answer continues…

    1. I have omitted the tin foil and keep the skin on while roasting or cooking. That seems to have cleared up the problem for me. I’ve planted plenty of beets in the garden this year, so I’ll let you know if it happens again.

      1. I am wondering if I peeled and cut my beets too far in advance of putting them in with the pork ribs. Perhaps certain beets were exposed to the air for too long. I have been making borscht for years and this is the first time I have had a situation with the beets.

        1. Hi Gail,
          I’m still working on this puzzle. My requests to various Agricultural Departments and Veggie Crop specialists have been met with silence. My own experiments have not resulted in a definitive answer. But I will continue to work on it.
          Thanks for sharing your experience.
          Getty

  21. My beets just turned black.. almost completely black. The golden beets are a shade of dark grey. All the way through!

    I had roasted with an aluminum foil cover the baking and left them in the oven overnight to cool.

    They had their skins on, though, so that’s not the issue.

    1. Oh no, Lidia! I know how disappointing that is. Skin on or off I guess wrapping them in aluminum foil is not the best idea. Thanks for sharing your results – as frustrating as they may be.

    2. I have peeled, boiled and sliced golden beats twice. Only after refrigerating do they get black near the center of the beet. I even vacuum sealed a couple to see if oxidation was causing a chemical change. The spots still appeared so I’m debunking the aluminum foil and oxidation leaving only one conclusion, a collection of starch much like a bruised banana.

      1. I think you’re on to something Victor. My latest theory is that refrigeration might be a culprit. When potatoes are stored at cold temperatures and then later boiled they sometimes turn black. Could the same be happening to our beets? I’ll be experimenting with this summer’s beets. Cooking a batch from the garden with and without refrigeration.

    3. Is anyone using salt in the cooking process is it possible that iodine in the salt is reacting with the starch which I know turns black, take a small amount of iodine in a cup of water add tiny pinch flour, it turns black.

          1. If the yellow beet is black on the inside say like if it had seeds if you cut that out are they safe to eat?

          2. Hi Chris,
            We may be talking about two different kind of vegetables. The beets I’m talking about are root vegetables, both the red beets and yellow beets are pulled from the ground. They would never have seeds in them, they are the root of the plant. The leaves growing out of the roots are dark green to dark burgundy in color. If left to grow long enough, they will send up a stock that will eventually flower and form seeds.
            I’m not sure what kind of vegetable you are cutting into, but I highly recommend you do not eat anything that you can’t identify.

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