International Produce Training

Apples- Russeting (Stem or Calyx Basins)

Russeting on apples is a common quality defect.  To help you understand what russeting is, the following comes from Kansas State University:

Description: A tan-colored, corky tissue on the surface of apples is often called ‘russeting’ and is caused by damage to epidermal cells. It is a condition of the ‘skin’ only, so the usability of the apple is not reduced. Golden Delicious is one of the most susceptible varieties while red varieties are not as likely to develop russeting to any degree. Possible causes of russeting include:

* Wetness from heavy dew or rainfall on the fruit surface for several hours when the fruit was initially developing, along with cold temperatures during the late bloom period

* There is also some relationship between the use of certain pest control materials that contain sulfur, copper, zinc, calcium as well as products formulated as emulsifiable concentrates and an increased level of russeting

* Various fungi including that which causes powdery mildew (Podosphaera leucotricha) and bacteria have been associated with russeting

* Excessive fertilization

Recommendations: Although russeting can result in an unappealing appearance of the fruit, it is a condition that is only ‘skin deep’ and will not influence the use or storage of the apples unless the russeting leads to fruit cracking. Practices that can reduce russeting include the following.

* Plant varieties less susceptible to russeting.

* Prune trees for better air movement and thin fruit to one about every 4 inches on average.

* Avoid spraying emulsifiable concentrates. Wettable powders are less likely to cause damage.

The USDA has specific scoring guidelines when russeting is encountered.

Looking at the apples seen above, you can clearly see the russeting on these apples and the defect seems to detract from the appearance.  But, the U.S. Grade Standards for Apples states:  “Russeting (except russeting that is rough or bark-like) in the stem cavity or calyx basin which cannot be seen when the apple is placed stem end or calyx end down on a flat surface shall not be considered in determining whether an apple is injured by russeting.”  If these apples were placed stem end down, on a flat surface, the russeting would be hidden, thus the USDA deems this is not a defect.

OK, if that’s what the standard says, then we accept it.

But how about these apples seen above?  Let’s take this defect step by step.

Step 1- Is this russeting affecting the calyx basin; because if it is, according the Grade Standard it is to be ignored?

Answer:  No, this is a scar is caused by an insect, the Plum Curculio insect. An insect sting is a small insect puncture, which extends only slightly below the skin of the fruit while a worm hole continues well into the flesh and is unusually larger.  The larva of a codling moth is the most common insect causing stings and worm holes.  Generally all insect feeding punctures and actual holes made by insects will be scored using the scoring guide for insect and worm holes

Step 2- If this is caused by an insect then it should be scored as a defect, correct?  The US Grade Standard states the following: “Any healed sting or healed stings which affect a total area of more than one-eighth inch in diameter including any encircling discolored rings.”

Answer:  No, the USDA states in their Inspection Instructions for Apples (not in the US Grade Standards) the following: “Punctures made by the Plum Curculio for the purpose of laying eggs usually result in crescent-shaped, corky, russet scars, which shall be scored on the basis of russeting rather than insects.”

Step 3- So, if the USDA states this defect, caused by the Plum Curculo insect, is scored as a defect using the same scoring guidelines established for russeting, this defect would be ignored, because it is affecting the calyx basin, not visible when placed on a flat surface?

Answer: Yes.

You may be wondering why I made it a point to say this guideline is not written in the US Grade Standard, but it is found in the USDA Inspection Instructions for Apples……what’s the difference?  All grade standards are published in the Federal Register and are open to comments from all members of the produce industry.  If a grower/shipper, or retailer/wholesaler would like to see a change to a standard there is a process to follow.  The USDA’s Inspection Instructions are developed in-house, by the USDA, without a vetting process.  Scoring guidelines found in Inspection Instructions can be changed simply by the USDA making the change.  You can imagine for yourself how this process works (or doesn’t work).

One Comment on “Apples- Russeting (Stem or Calyx Basins)”

michael walker Says:

while reading and watching the slides i am learning a lot about defect and apples.

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