Peel damage, Abrasion damage

The injuries affecting tubers fall into four categories according to the level of damage to the skin and the underlying cell layers:

• Peel damage
• Shatter bruises
• Internal black spot
• Pressure bruising

In all cases, mechanical damage observed on tubers has been caused by shocks they have received during harvesting or handling operations (bulk or box filling and packing etc.). The force, angle and direction of the impact, the degree of suberisation of the skin and the physicochemical characteristics of the tuber (dry matter and tyrosine content, cell turgor pressure etc.) result in the appearance of one of the symptoms described in this chapter.

Symptoms on tubers

Scratches, abrasions and peel damage are examples of superficial damage involving a partial loss of skin (exfoliation) on the surface of the tuber. Under the effect of enzymatic browning, this may cause the formation of rust-brown areas likely to seriously spoil the visual aspect of the tuber (photos 1 to 4). This may also result in significant weight losses during storage and increase the risk of burns caused by the use of sprouting inhibitors in storage.

Control

Skinning are typical signs of tubers that have been lifted before complete maturity. They are observed chiefly on early tubers, on seed potatoes or ware potatoes whose skin is insufficiently suberised, e.g. haulms destroyed prematurely, too short a retention time in the soil and excessive nitrogen fertilisation.

Preferably, harvesting must be done when the tubers have had sufficient maturation time in the soil to have a well suberised skin. At the same time, it is necessary to avoid too dry conditions.

During harvesting, the settings must be very accurately adjusted: chain rotation speed consistent with the engine speed (ideally, a ratio of 0.8 to 1.2), minimum shaking, minimum aggression by devices used for the elimination of haulms and clods.