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I had many potatoes I wanted to preserve for a long time. Usually the potatoes I keep in my kitchen get rotten after a month or two (and I don't have a cellar to keep them cool), I decided to dehydrate them. So I grinded them in a food-processor and put in a food-dehydrator in 65 Celsius. After several hours they became dry but also got colored black - a strong black color on the (previously) white potatoes and a weaker color on the red potatoes.

Is there anything useful I can cook with these potatoes that turned black?

  • Did you peel them before grinding them? – GdD Aug 27 '14 at 8:16
  • @GdD yes, I peeled them. – Erel Segal Halevi Aug 27 '14 at 10:25
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Throw them away. I would not expect potatoes to go black in the dehydration process, and although they may be safe to eat I would not expect them to be palatable, or inviting in any way. You cannot be sure they aren't toxic, and you wouldn't put them on a guest's plate, so chuck them.

  • Indeed. They do go black after a long exposure to air in room temperature so any other indicators of foulness are void. – Captain Giraffe Aug 27 '14 at 22:01
  • The potatoes sat on the shelf for a long time and my wife didn't want to touch them. So you are probably right... I will have to throw them away. – Erel Segal Halevi Sep 10 '14 at 7:15
  • Hey, it was worth a try. – GdD Sep 10 '14 at 7:29
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The color on the potatoes is attributable to the oxidation that's a natural degradation process. The main cause is the direct exposure with open air but other factors can accelerate it (even the metal on the knife or the food processor's blades in your case). Some vegetables are more susceptible than others (for example, avocados turn black in a matter of minutes). There are some methods to slow this transformation like a bath in water mixed with some acid (lemon, vinegar ...) or baking soda. Now the good news: the result of oxidation is not toxic, the worst thing is that the more the process goes on the more vitamins the food lose. In your particular case, I think the food-dehydrator contributed to the oxidation. Since now they're dehydrated you sould regenerate them with a liquid and then you can try to cook them (maybe some puree) but you won't get back the nice clear color, they'll keep looking ... bad.

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    Oxidation is indeed common in potatoes, but it is a warm brownish colour. I doubt that somebody will describe it as "black". – rumtscho Aug 26 '14 at 12:17
  • @rumtscho I agree with your comment. I don't know, but wondered if the low temperature of the dehydrator over a period of several hours could have possibly made them unsafe to eat. Any ideas on this? – Cindy Aug 26 '14 at 13:34
  • @CindyAskew the danger zone starts at 60 Celsius, so it is just high enough not to be unsafe. Some unusual handling could allow bacterial growth though, or the potatoes could have caught some culture which is heat resistant. 60 Celsius doesn't stop all bacteria from multiplying, just the common disease causing ones. Frankly, I have no idea what the cause is based on that description, chemical and biological is both possible - but simple oxidation sounds very unlikely. – rumtscho Aug 26 '14 at 14:00
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    I think this extract from a book could help understand the problem a little more or at least, since there's a color picture, try to understand if it the same color @Erel-Segal-Halevi is referring. It's the description of a homemade test, so you won't find lab measurements or particular references to papers or pubblications, sorry about that. – Stefano Driussi Aug 27 '14 at 7:51
  • @StefanoDriussi the black color on my potatoes is similar to the black color in the top of the two cups. – Erel Segal Halevi Aug 27 '14 at 12:10
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I just dehydrated things for the first time yesterday, mainly russets. I saw something in the instructions about preparing potatoes but neglected to follow through. They were reeeeaaally black. I mean, they brought to mind black mold. But I knew it couldn't be that. They taste fine, but aren't attractive. I'm going to use them as snacks over the coming week. I ain't scared. It's not like I'm serving them to guests, which I wouldn't do. Next time I'm blanching, as strongly recommended by the following website. http://www.gettystewart.com/dehydrating-potatoes/

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I dehydrate potatoes all of the time, you need to slice them then boil them for 6to 8 minutes drain the water good then you can dehydrate them, if not they will turn black.

  • This does not answer the question, but another one: 'How can I dehydrate potatoes?' – user34961 Aug 31 '17 at 6:31

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