Freezing

Tuber Internal Growth Defects: FREEZING

Freeze injury to tubers can occur in the field, in storage or in transit due to exposure to below freezing temperatures, <30oF. In storage of seed and table stock tubers, freezing is usually associated with poor ventilation and poor insulation.

External Appearance:

Prior to thawing, affected tuber area is hard. After thawing, affected tuber area appears wrinkly and flabby. It may have a "weeping" effect, that is, water will leak from tuber surface.

Diagnostic Method:

Cut through affected area.

Internal Appearance:

Although seemingly similar to chilling, the underlying tissue will be bluish-grayish and the margin will be sharply defined, not diffuse. Also, unlike chilling, there will not be a net necrosis. Upon thawing, affected tissue will gradually change from a dull, off-white (grayish) color to pinkish-reddish to brown-black. The tissue breaks down from being hard (frozen) to a watery texture, soft and wet.

Cooking Appearance:

Not suitable for table stock or processing. Tissue breaks down during cooking, such as sloughing during boiling and becoming a watery mush during baking. May be used for dehydration.

Development:

Ice crystals form in cells upon freezing. These puncture the cell and organelle membranes. Upon thawing, the cells loose structural integrity and spill out their contents. Bacterial soft rot commonly will attack thawed affected tissue in storage. Don't use for seed due to poor sprouting and high susceptibility to soft rot.

Control Measures:

Avoid exposure to temperatures below 30oF. If freeze occurred in the field, discard affected tubers; don't store them. Don't mix tubers from fields exposed to a freeze (tend to get soft rot) with those that weren't.

  1. Harvest before soil temperature drops to freezing.
  2. Tarp truckloads.
  3. Don't store against an outside wall.