This time of year my potato supplier says that it’s natural to have potato bruising. What exactly does that mean? What causes it?

A great deal of planning, time, money and effort is required to produce a high quality Idaho® potato crop. But all of these investments by Idaho growers and shippers are of little importance when potatoes reach the foodservice operator in prime condition are then damaged by mishandling.

Despite their hardy appearance, potatoes can be bruised as easily as a banana or an apple.

They are living organisms made up of a network of cells that form skin (cork layer) and inner tissue (cortex). Bruising occurs when the tissue is crushed and cells rupture, releasing enzymes that produce a black discoloration. There are two types of bruising-internal bruising and shatter bruising.

INTERNAL BRUISING. Sometimes referred to as blackspot, internal bruising happens when potatoes are dropped more than six inches, or if something heavy is placed on top of them. The amount of bruise is directly related to the fall. It can appear beneath the surface of the skin, or penetrate deep into the tuber. The damage does not appear immediately, but becomes noticeable after one or two days in storage. Since the skin is not broken, the damage may not be found until the potato is cut or pared.

This type of internal bruising frequently takes place when potatoes are dumped into a display bin, dragged along a storeroom floor, potatoes are crushed in a carton when stacked under  several others or dropped into a shopping cart.

SHATTER BRUISING. Shatter bruising occurs when the skin of the tuber has been broken. The potato then produces a substitute covering known as wound or scar tissue. This is usually a thick unsightly layer that is hard to peel and result in excessive waste. Shatter bruising happens most often when potatoes have been refrigerated. The inner tissue becomes brittle and susceptible to impact damage.

To avoid bruising, potatoes should be handled as little as possible. Store them in a cool, dark, well-ventilated place, at 45*F. to keep the bruised area from spreading or rotting and possibly damaging surrounding spuds.

The Idaho® Potato Commission wishes to thank Robert Dwelle, Ph.D., Associate Professor of Potato Physiology, Idaho Research & Extension Center, for his expertise and assistance with the preceding information.