Black pattern inside a raw potato?

March 25, 2020



What you see: A black pattern inside your potato
What it is: A number of issues cause black areas to form in potatoes; the potato pictured above most likely spent too much time in a place that was too cold.
Eat or toss: Eat! This potato might be a little sweeter than normal. Cut around the black area if you find it unappealing. 


The story:
As we’ve seen in other EatOrToss adventures, when produce is kept too cold for too long, weird things happen. Potatoes are no exception. While a number of mishaps can cause black patterns to appear in potatoes, the most likely issue here is something called “chilling injury.”


Stored somewhere south of 38 degrees Fahrenheit for too long, this potato’s cells suffered damage, resulting in that smokey black effect. It’s unappealing, but not a safety issue. 


Might taste sweeter
Low temperatures also cause potatoes to convert some of their starches to sugars, which means that both the black areas and the normal-looking areas in this potato might taste sweeter. But the starch to sugar transition is reversible. If, after being exposed to cold, the potato were then stored at warmer temperatures, the sugar and starch levels may have gone back to normal, explained Nora Olsen, professor and potato specialist at the University of Idaho. 


Tubers harvested too early are more sensitive to cold temperatures, but just because these are little potatoes doesn’t mean they were pulled from the field prematurely—they just happen to be potatoes that only get so big.  


Unexpected browning in fries and chips, another sign of chilling injury
Chilling injury in potatoes doesn't always advance to smoky streaks. Fries or chips that brown in unexpected areas may be showing the effects of too-cold storage (the brown is essentially those unwanted sugars browning in the heat). The same goes for potatoes that turn black after boiling. 


And, fortunately, this potato never got so cold that it froze. Freezing injury is much worse, leaving the tuber soggy and then chalky as the water dissipates. 


Many scenarios can lead to black areas inside potatoes
Chilling injury can happen while potatoes are still in the field, while they’re in storage after harvest, or while they’re in transit. Could you cause chilling injury by storing your potatoes in the fridge? Olsen said research on typical household fridge temperatures' effects on potatoes is limited. However, if you put some potatoes in your freezer for a couple hours, you might be able to bring about chilling injury (but please don't, #nofoodwaste). 


And, just to cover our bases, while this potato seems most likely to be suffering from chilling injury, a number of scenarios can turn potatoes black on the inside.  Tubers that are oxygen deprived, either from flooding or being stored in a low-oxygen environment can get something called “blackheart.” Some potato pathogens can cause internal blackening. 


So don’t worry about a potato like this, but do steer clear of anything mushy, fuzzy or moldy. 


Thanks to Brian Lipinski of Washington, DC for submitting this photo of his potato! In addition to trying to make the most of produce in his home kitchen, Brian works on food waste reduction at the World Resources Institute. Check out WRI's 10-step plan for the world to cut food waste and loss in half by 2030. 




Nora Olsen. Professor and potato specialist. University of Idaho. 
Biochemical and molecular control of cold-induced sweetening in potatoes. Joseph R. Sowokinos. American Journal of Potato Research. May 2001.
Tuber Internal Growth Defects: CHILLING. Institute of Agriculture and Natural Resources. CROPWATCH. University of Nebraska - Lincoln. 
Chilling and Freezing Injury. Chien Yi Wang. Produce Quality and Safety Laboratory, USDA, ARS Henry A. Wallace Beltsville Agricultural Research Center, Beltsville, MD 

Vegetables Produce Facts - Potato, Early Crop. Recommendations for Maintaining Postharvest Quality. Trevor V. Suslow and Ron Voss. Department of Plant Sciences, University of California, Davis

Internal temperature-shock injuries. Working Party on Agricultural Quality Standards Specialized Section on Standardization of Seed Potatoes Fortieth session Geneva, 14-16 March 2011

Compendium of Potato Diseases. W. J. Hooker. P. 8. International Potato Center. 1981. 

Diseases, Pests and Disorders of Potatoes: A Colour Handbook. Stuart Wale, H.W. (Bud) Platt. Nigel Cattlin. 2008. Manshon Publishing. P. 154 - 158. 

Frost Necrosis of Potato Tubers. Lewis Ralph Jones, M. Miller, E. Bailey. Agricultural Experiment Station of the University of Wisconsin. 1919.

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© 2020 by EatOrToss.

Content may not be duplicated without express written permission from All information posted on this blog is thoroughly researched, but is provided for reference and entertainment purposes only. For medical advice, please consult a doctor. Please see our terms