PI-009: Seed Potato Tuber Inspection
Appendix 10: Pressure Bruises

This page is part of the Guidance Document Repository (GDR).

Looking for related documents?
Search for related documents in the Guidance Document Repository

Pressure bruises develop in storage on tubers usually late in the season. Tubers are most susceptible to pressure bruising when the humidity in storage drops below 90% causing the tubers to lose moisture, particularly in the initial months of storage. This defect is most often the result of pressure at points of contact with adjacent potatoes, or the floor and appears as flattened or depressed areas on the tuber (80). In most instances, there will be no discolouration of the underlying flesh at time of packing; however, grayish to black discolouration may develop in the affected tissue with time (81). It is impossible to predict whether discolouration will occur, or how extensive it will be, from the appearance of the flattened or depressed areas. Over time pressure bruises may become sunken (82, 83) and develop into a rot (84)Footnote 9.

80 | Pressure bruise
80 | Pressure bruise. Description follows.
Description for 80

This is an image of a potato demonstrating a pressure bruise. The defect shown in this image is often the result of pressure at points of contact with adjacent potatoes, or the floor. It appears as a flattened or depressed area on the potato. This bruise takes up around 30% of the surface area of the side of the potato that is shown, and is a slightly grey colour.

81 | Pressure bruise with internal discolouration
81 | Pressure bruise with internal discolouration. Description follows.
Description for 81

This is an image of a potato demonstrating a pressure bruise. This potato has a dark brown skin with a cream coloured interior. The end of the potato has been peeled off and placed beside the potato in order to demonstrate the bruise occurring both on the outside and inside of it. The bruise takes the form of a grayish to brown to black discolouration and covers only 10% of the surface of the side of the potato that is shown.

82 | Pressure bruise
82 | Pressure bruise. Description follows.
Description for 82

This is an image of a potato demonstrating a pressure bruise. This potato has a dark skin, with it still intact. On the side of the potato that is viewed there is a pressure bruise that has sunken in. The bruise takes up 30% of the viewed side’s surface area.

83 | Pressure Bruise
83 | Pressure Bruise. Description follows.
Description for 83

This is an image of a potato demonstrating a pressure bruise. The potato has very light skin and almost appears dusty and covered in soil. The bruise is on the top side of the potato and has sunken in. The bruise takes up 40% of the top side’s surface area.

84 | Wet pressure bruise
84 | Wet pressure bruise. Description follows.
Description for 84

This is an image of a potato demonstrating a pressure bruise. This potato has a dark brown skin. The bruise is on the top side of the potato and has sunken in. This bruise takes up 75% of the top of the potato’s surface area; because of the rot that has begun, the sunken portion appears slightly moist, with dark brown and black rings forming on its edges. The spot itself is a dark brown colour.

(85) Pressure bruises are scored under a special tolerance for pressure bruises when the sunken and discoloured areas are in excess of 10% of the surface area of the tuber. To approximate percentage coverage, tubers can be divided into quadrants as illustrated below. This is a two dimensional image, one side is shown as 50 %; this represents one half of a tuber sliced down the middle.

86 | Pressure bruise scoring
86 | Pressure bruise scoring. Description follows.
Description for 86

This image shows four pictures of the same potato with a pressure bruise. The first image shows just the potato with the pressure bruise. The second image shows the pressure bruise outlined in yellow. The third image shows the pressure bruise covered with white showing just the remainder of the tuber. The fourth and final image has the pressure bruise cut out and super-imposed on the tuber; the tuber is marked to show the percentage that the super-imposed cut out of the pressure bruise covers.

Date modified: