When do you know that potatoes are bad?

When do you know that potatoes are bad?

Pawel Malczewski
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Short Summary

While green potatoes are the most obvious sign that they have gone bad, there are other, less evident, signs that you have to consider before eating potatoes.

This article provides insights on how to recognize the potatoes that are bad and should not be eaten. It also provides optimal buying and storage tips. For a quick answer click here.

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Explanation

How can you tell when potatoes are bad?

Even after harvesting, potatoes continue to live”, which means that they still absorb oxygen and release carbon dioxide. Potatoes stay in this dormant state for 1 to 4 months (depending on the variety), until they start sprouting.

The process of respiration and change from a dormant to a sprouting stage considerably reduces the nutritive value and begins the process of deterioration of potato until it becomes unfit for consumption. It can manifest in various ways.

The following list describes how to spot a bad potato that is unfit for consumption (1)Sprout suppression on potato: need to look beyond CIPC for more effective and safer alternatives. Paul V, Ezekiel R, Pandey R. Available here. (2)Rich AE. Potato diseases. Academic Press. January 1983. Available here.:

Green potatoes – indicate toxicity, which may lead to serious health consequences and even death. This includes potatoes with a green discoloration of the skin (whether in patches or the majority of the skin) or the flesh. Potatoes with any sign of green color should not be eaten. (read more..)

Sprouted potatoes – may indicate that the potatoes have either been stored for a long time or in warm temperatures. Depending on the variety, potatoes start sprouting naturally after more or less between 1 and 4 months of harvesting, unless they were treated with sprout suppressants.

Sprouted potatoes, especially if they are firm, don’t necessarily mean that they are bad for consumption.

The sprouts contain the same toxin as green potatoes, called solanine, which can be very toxic and should not be eaten. Therefore, before cooking potatoes, you should remove the sprouts.

However, potatoes with long sprouts and are soft or look wrinkled should not be eaten since it indicates advanced deterioration or spoilage. (3)MedlinePlus. Potato plant poisoning – green tubers and sprouts. Available here.

Wrinkled, sunken potatoes – indicate spoilage (dry or wet rot) and should not be eaten.

Potatoes with deep cracks – thumb-nail size cracks indicate rough storage and handling. The product may contain harmful microorganisms such as mold or fungus or may be spoiled. Choose potatoes without deep/large cracks.

Small and shallow surface cracks that look healed may be ignored since they indicate natural cracking that occurred during the growing process.

Soft or mushy potatoes – have reduced nutritional quality and may indicate spoilage. They should not be eaten. Pick only firm potatoes.

Potatoes with mold – not only indicates spoilage but mold is harmful for your health. Moldy potatoes are often damaged (cut or bruised) since the damaged area is the most vulnerable to mold formation. They should not be eaten.

Potatoes with a bitter taste – indicates that the potatoes contain solanine – a poisonous substance. Bitter potatoes should be discarded.

When you can tell that potatoes are bad

How to store potatoes

To maintain the quality and freshness of the potatoes and to prevent them from going bad, there are a few hints on buying and storing potatoes.

Buying potatoes

  • Buy from trusted sources, that consistently sell good quality potatoes;
  • Buy only the amount you intend to use within the next few days in order to avoid long term storage. However, if you are going to use the potatoes within a week, don’t worry about storage, just use common sense and the usual storage methods.
    They will not go off in that short period of time unless they will be kept in extreme conditions. (details below);
  • Preferably buy organic potatoes to reduce the amount of chemicals.

How to store potatoes

In case you need to store the potatoes for a long time, you will need to make sure that the storage area and method is adequate to avoid potato spoilage or toxicity. The following are descriptions of the best ways of storage potatoes.

  • In an area with some degree of humidity to avoid dehydration and becoming wrinkled and withered;
  • In a dark area to prevent greening of potatoes. The greening process may occur from exposure to sunlight, indirect daylight and artificial light;
  • In a well ventilated area to prevent rotting;
  • In an ideal temperature, that varies, depending on the source, from about 8 to 12 degrees Celsius (46-54 Fahrenheit) (4)Sprout suppression on potato: need to look beyond CIPC for more effective and safer alternatives. Paul V, Ezekiel R, Pandey R. Available here. or 5 to 9 degrees Celsius (41-48 Fahrenheit). Generally, the storage temperature of potatoes should be higher than 2 degrees Celsius (36 Fahrenheit) and lower than 12 degrees Celsius (54 Fahrenheit). (5)Aung MM, Chang YS. Temperature management for the quality assurance of a perishable food supply chain. Food control. Volume 40, June 2014, Pages 198–207. Available here. (6)Jobling J. Temperature management is essential for maintaining produce quality. Sydney Postharvest Laboratory Information Sheet. Available here. (7)Aml EA, Moghazy AM, Elshatoury G, Elshatoury RSA. Inhibition of Sprout Growth and Increase Storability of Processing Potato by Antisprouting Agent. ScienceAlert. Available here.The best home storage areas are a cool garage, cellar, basement or pantry. If you don’t have any of these storage areas, the refrigerator set to a slightly higher temperature than usual is a good alternative.Storing potatoes at warmer temperatures, such as at home temperatures (which are on average about 68 degrees Fahrenheit/ 20 Celsius), may result in a quick reduction in of the potato quality and in the growth of microorganisms, fungus and sprouts.In cooler temperatures, from 0 to 2 degrees Celsius (32 to 36 Fahrenheit), starch present in potatoes turn into sugar, making them taste sweeter. If the potatoes have developed a sweet taste, due to cold storage, place them in the higher temperature of about 15 Celsius (59 Fahrenheit) for 1-2 weeks. This is especially important if you want to fry the potatoes (chips/French fries).

    Chips from potatoes stored between 1-2 degrees Celsius (34-36 Fahrenheit) are darker. Cooking or baking theses potatoes doesn’t have a darkening effect. (8)Kumar D, Singh BP, Kumar P. An overview of the factors affecting sugar content of potatoes. Annals of applied biology. 145, Issue 3. December 2004. Pages 247–256.Annn Available here.

    Potatoes can withstand temperatures slightly below 0 degrees Celsius (0 to –2 degrees Celsius or 32 to 28 Fahrenheit) provided they are not damaged. The flesh of damaged potatoes will develop a red, brown or grey color and will lose its quality. Potatoes are often stored or transported by retailers at temperatures between -1 and -2 degrees Celsius (30 and 28 Fahrenheit).

    Temperatures below -2 degrees Celsius (28 Fahrenheit) cause a break-down of the tissue of the potatoes, where tissue cells rupture. After thawing, the potatoes become wet and often contaminated with bacteria, causing a bad smell.

  • To maintain the potatoes’ moisture and to provide them with fresh air, store the potatoes in a perforated plastic bag. Potatoes should not be stored in airtight containers. Storing potatoes in a perforated bag also reduces their moisture (and weight).
  • Don’t wash potatoes before storing them.

NOTE ON CONSUMPTION OF RAW POTATOES: raw potatoes can be juiced. While drinking fresh potato juice is safe, if you want to eat potatoes you need first to cook them in order to avoid stomach upset. (read more..)

Conclusion

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Avoid potatoes that are green, wrinkled, soft, mushy, moldy, with scars or bruising and if they have a bitter taste. Sprouts need to be discarded before cooking the potatoes.

When storing potatoes, insure that there is a humid, dark cool area with a good air flow to avoid spoilage, sprouting, drying out, and starch turning into sugar.

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References   [ + ]

1. Sprout suppression on potato: need to look beyond CIPC for more effective and safer alternatives. Paul V, Ezekiel R, Pandey R. Available here.
2. Rich AE. Potato diseases. Academic Press. January 1983. Available here.
3. MedlinePlus. Potato plant poisoning – green tubers and sprouts. Available here.
4. Sprout suppression on potato: need to look beyond CIPC for more effective and safer alternatives. Paul V, Ezekiel R, Pandey R. Available here.
5. Aung MM, Chang YS. Temperature management for the quality assurance of a perishable food supply chain. Food control. Volume 40, June 2014, Pages 198–207. Available here.
6. Jobling J. Temperature management is essential for maintaining produce quality. Sydney Postharvest Laboratory Information Sheet. Available here.
7. Aml EA, Moghazy AM, Elshatoury G, Elshatoury RSA. Inhibition of Sprout Growth and Increase Storability of Processing Potato by Antisprouting Agent. ScienceAlert. Available here.
8. Kumar D, Singh BP, Kumar P. An overview of the factors affecting sugar content of potatoes. Annals of applied biology. 145, Issue 3. December 2004. Pages 247–256.Annn Available here.

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