Potatoes in the Refrigerator=no-no

The lowly potato is a marvel of the botanical world, biochemically.  Depending upon the stage of its life, it can self-heal, create sugars, create starches, and turn one back into the other.  The potato is a member of the Solanaceous family which includes the tomato, the eggplant, tobacco and Nightshade.  People have selected the white Irish potato for the storage tuber it creates underground during the growing season.  It grows fairly well for a member of the Solanaceous plant family since they usually need quite hot weather to do well.  White potatoes can thrive in cool rainy seasons and still store starches in underground tubers. 

Another selection trait that humans must have considered is the production of toxins by the potato.  The people of the Andes must have favored the types with less of the toxic alkaloid, Solanine.  The potato plant produces this in the above ground parts to avoid being eaten by animals.  The Solanine is concentrated in the fruits and seeds of many members of the family.  Potatoes also deposit it in the tubers in response to damage or sunlight. 

Many times you will see the shoulders of the potatoes peeking out of the ground around a plant.  The plant turns the parts exposed to sunlight green with chlorophyll.  It also will build up Solanine in the area just under the skin.  It is assumed that green potatoes will sicken people who eat them but this is very rare in our commercial varieties.  Apparently Solanine develops indepently from chlorophyll so the green color is not a true indicator of the toxin.  It may develop from improper handling and storage or damage from rot.  If you are trying to salvage damaged potatoes, you would want to peel them down and discard a wide amount near a rotten spot. 

Another reason that potatoes now-a-days are seldom harmful is that the potato of commerce is all Solanum tuberosum spp. tuberosum.  The vast majority of potatoes commercially grown are of one cultivar also, the ‘Russet Burbank.’  It is easy to grow although prone to insect and disease attack.  In response to decreasing day length, the potato plant puts its reserves of carbohydrates into the tubers.  After harvesting, the tubers are bumped and bruised and scratched no matter how much care is taken in their unearthing.  The next step is usually curing.  This is done to repair damage and thicken the skin to keep from dehydration and spoilage.  The storage room is held at a high temperature to rev up the tuber’s metabolism and form corky skin cells.  Temperatures of up to 122 degrees or more and low humidity are normal. 

After curing, potatoes are stored at the lowest possible temperature that decreases their metabolism but avoids chilling injury.  As we have seen, chilling injury can produce toxins.  It also causes the creation of ethylene gas.  Ethylene is not good for potatoes.  It makes them start to ripen and soften similar to a banana.  The texture softens and the starches start to change into simple sugars, not long chain carbohydrates.  The taste begins to sweeten.  If you were to cook with them this way, they would taste sweet and they would brown, not stay white, when the sugars carmelize with heat.  And this is why you should not keep the potato in the refrigerator!  Toxins, softening, taste, color, what more do you need?

Commercial storage facilities are very careful to keep potatoes cool but not cold.  They also have ethylene scrubbers to reduce ripening.  Before sale, the potatoes are gradually warmed up to within 9 degrees of ambient temperature.  This is to avoid condensation when the product is removed from storage to be packaged and sent out.  The consumer is then supposed to store the potatoes in the mesh bags at room temperature, in the dark.  The stored starches will stay as starch and not turn sugary until the tuber begins to rot, about a month to 6 weeks after purchase.

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