WARC apple maturity 10/13/2020

Apple Starch-Iodine test results for 10/13/2020 at WARC (Corvallis).

Cornell Starch-Iodine Index for apple maturity.  Fully stained fruit are rated 1 = less mature (less ripe), fruit with little to no stain are rated 8 = most mature (ripe).

 

Cornell starch iodine scale for apples

Blanpied, G.D. and S.J. Silsby. 1992, Predicting Harvest Date Windows for Apples. Cornell Cooperative Extension. Information Bulletin 221.

 

The starch-iodine index is a method to assess apple maturity (ripeness).  Fruit can either be sprayed or dipped in an iodine solution. After two minutes, fruit can be visually compared to rating scales to rank their maturity. 

Test principles.  As apples ripen, starch is converted to sugars. The iodine in the test solution binds to starch in the fruit: the more purple-black stain on a fruit, the less mature or ripe the fruit is. 

Visual rating scales.  Several rating scales exist. We are using the Cornell Starch-Iodine Index [1], which ranks fruit 1-8, with 1 being less ripe, and 8 being fully ripe. A 1-6 scale is popular with Washington growers, and due to unique starch patterns, a separate scale for 'Honeycrisp' has been developed [2].

Utility.  For dessert apple cultivars, picking fruit at optimal maturity for either fresh eating or for storage is an important part of marketing fruit. For cider apples, research suggests cultivar has more impact than ripeness on volatile profiles (aroma) of resulting ciders in one study [3], and phenolics were not greatly impacted by apple maturity (ripeness) in another [4]. In Montana, hard cider varieties tend to be picked at more advanced maturity or what would be considered overripe for dessert varieties.

How to obtain the iodine solution.  Pre-mixed iodine solution can be purchased through Wilson Irrigation in Yakima, WA. Virginia Cooperative Extension also has recipes for making the solution detailed in Harvest Maturity Resources [5].

Other tools for assessing fruit ripeness.  Brix (a measure of sugars), firmness, and other tools can also be used to assess fruit maturity and quality. See Apple Maturity and Harvest [6] by Washington State University for further details.

Weekly photos of starch-iodine testing at Montana orchards

8/25 - 10/13/2020 (in order from most recent to oldest)

Photo 1 of 2. Apple cultivars shown: 'Dabinette,' 'Chisel Jersey,' 'Cortland'Photo 2 of 2. Apple cultivars shown: 'Ashmead's Kernel,' 'Binette Rouge'Apple cultivars shown: Muscadette de Dieppe, Ashmead's Kernel, Dabinette, Binette RougeApple cultivars shown: Cortland, Chisel Jersey, McIntoshApple cultivars shown: Wealthy, Chestnut Crab, Sweet 16, Dalgo CrabApple cultivars shown: Chestnut Crab, Muscadette de Dieppe, Dabinette Apple cultivars shown: 'Cortland,' 'Ashmead's Kernel,' 'Wealthy'Apple cultivars shown: Chisel Jersey, McIntosh, Hewe's Crab, Binette RougeApple cultivars shown: Wealthy, Chestnut Crab, McIntoshApple cultivars shown: Hewe's Crab, CortlandApple cultivars shown: Dabinette, McIntosh, Wealthy, Hewe's Crab, Muscadette de DieppeApple cultivars shown: Cortland, Chestnut Crab, Binette Rouge, Chisel Jersey, Ashmead's KernelApple cultivars shown: 'Honeycrisp,' 'Prairie Magic,' 'Goodland,' 'Chestnut Crab,' 'Frostbite,' 'Zestar!'Apple cultivars shown: unknown, Wealthy, State Fair, Norland, Dalgo Crab, Chestnut CrabApple cultivars shown: Sweet 16, Mantet, Harel Red, New York 702, Geneva EarlyApple cultivars shown: Duchess and Wealthy Apple cultivars shown: Honeycrisp, Wealthy, Ginger Gold, Frostbite, GoodlandApple cultivars shown: McIntosh, Jelly Crab, Wealthy, Whitney Crab, Yellow TransparentApple cultivars shown: Wealthy, Mandan, Atlas, Chestnut Crab, Dakota Gold, Beacon, Wolf RiverApple cultivars shown: Breaky, Collett, Goodland, Idared, Whitney CrabApple cultivars shown: McIntosh, Chestnut Crab, Cortland, Wealthy, Hewe's CrabApple cultivars shown: Frostbite, Chestnut Crab, Goodland, Prairie Magic, Zestar, Honeycrisp Apple cultivars shown: Hewe's Crab (Virginia Crab), Muscadette de Dieppe, McIntosh, WealthyApple cultivars shown: Ashmead's Kernel, Chestnut Crab, Cortland, Binette Rouge, Chisel Jersey, Dabinett

Click on an image to view as a slideshow.

Starch-Iodine Index of apples at Montana orchards

Big Sandy (Bob Quinn's orchard)

Bozeman (MSU-Bozeman Horticultural Farm)

Bozeman (Sypes Canyon/Alexander orchard)

Corvallis (MSU-WARC orchard)

Lodge Pole (Wasay Wakpa orchard)

Pryor (Chief Plenty Coups State Park orchard)

Townsend (Thompson orchard)

Whitehall (Redmond orchard)

Big Sandy (Bob Quinn's orchard)





 Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
9/1/20
Cultivar Harvest Date S-II n
'Atlas'   7.0 1
'Beacon'   7.0 1
'Chestnut Crab'   2.5 6
'Dakota Gold'   1.0 1
'Goodland'   5.0 1
'State Fair'   6.6 5
'Wealthy'   5.8 5
'Wolf River'   2.0 5

Bozeman (MSU-Bozeman Horticultural Farm)

Visit the Horticultural Farm's website.





 Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
9/1/20*
Cultivar Harvest Date Yield/Tree (lbs) S-II n
'Breakey' 9/5  9.92 3.4 10
'Collett' 9/5  38.80 4.9 10
'Goodland'     3.5 4
'Idared' 9/5  81.35 3.3 10
'Whitney Crab' 9/4  20.94 3.9 10

NOTES

9/1/20: a lot of dropped fruit

Bozeman (Sypes Canyon/Alexander orchard)

Large 1900s orchard with many additions over the years. 

   Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
9/5/20 9/25/20
Cultivar Harvest Date S-II n S-II n
'Chestnut Crab'   1.3 10 7.9 10
'Dalgo Crab'   1.1 10 8 10
'Geneva Early'   2.0 10 - -
'Harel Red'   1.2 10 - -
'Mantet'   3.4 10 - -
'New York 702'   3.4 10 - -
'Norland'   8.0 10 - -
'State Fair'   4.8 10 - -
'Sweet 16'   1.0 10 2.5 10
'Wealthy'   4.7 10 7.9 10
unknown variety   1.0 10 - -

NOTES

9/5/20: light fruit year; much fruit dropped already

Corvallis (MSU-Western Agricultural Research Center)

Sample size for tests = 10 fruits

   Starch-Iodine Index measurement date and value
Cultivar Harvest
Date		 8/15 9/1 9/8 9/15 9/22 9/29 10/6 10/13
'Ashmead's Kernel'   1 - 1.0 - 2.9 - 2.5 2.5
'Binet Rouge'   1 - 1.0 - 1.1 - 1.1 1.1
'Chestnut Crab'   1.2 1.0 2.3 2.4 2.3 - - -
'Chisel Jersey'   1 - 1.0 - 3.5 4.89 - -
'Cortland'   1 1.0 1.1 1.4 2.1 1.6 4.7 4.9
'Dabinett'   1 - 1.0 - 1.1 - 2.1 1.7
'Hewe's Crab' 9/17/20 1 1.0 3.8 6.5 7.5 - - -
'McIntosh' 9/10/20 1.6 2.2 2.1 3.3 4.3 - - -
'Muscadette de
Dieppe'		   1 - 1.3 - 2.9 - 2.3 -
'Wealthy' 9/15/20  1.2 2.2 2.5 5.1 6.1 - - -

Lodge Pole (Wasay Wakpa orchard)

   Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
 9/2/20
Cultivar Harvest Date S-II n Avg. approx. fruit
counts per tree
'Frostbite'    2.0 5 75
'Ginger Gold'    1.0 5 11
'Goodland'    3.9 5 7
'Honeycrisp'    1.0 5 33
'Wealthy'    5.0 1 4

NOTES

9/2/20: First fruit on some trees since planting. Limited fruit available.

Pryor (Chief Plenty Coups State Park heritage orchard)

   Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
 9/3/20
Cultivar Harvest Date  SI-I n 
'Duchess'   5.3 10
'Wealthy'   6.6 10

Townsend (Thompson orchard)

   Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
9/2/20
Cultivar Harvest Date  SI-I n 
'Jelly Crab'   6.3 3
'McIntosh'   2.6 3
'Wealthy'   3.0 5
'Whitney Crab'   3.0 5
'Yellow Transparent'   7.6 5

Whitehall (Redmond orchard)

   Starch-Iodine Index
measurement date, value
(S-II), and sample size (n)
 8/25/20  9/7/20
Cultivar Harvest Date S-II n S-II n
'Chestnut Crab'   1.0 2 3.2  10
'Frostbite Crab'   1.0 3 1.2  10
'Goodland' 9/4/20 2.5 2 4.7  10
'Honeycrisp'   1.0 1 1.0  10
'Prairie Magic' 9/1/20 7.3 3 8.0  3
'Zestar' 9/4/20 1.3  3 6.5  10

References

  1. Blanpied, G.D. and K.J. Silsby, Predicting harvest date windows for apples, Information Bulletin 221. 1992, Cornell Cooperative Extension Publication: Cornell University. p. 1-12. Available from: https://ecommons.cornell.edu/bitstream/handle/1813/3299/Predicting%20Harvest%20Date%20Window%20for%20Apples.pdf;jsessionid=AA54A3E7FD1F8262EA372ECF34AF9A52?sequence=2 (Accessed Sept. 11, 2020)
  2. Hanrahan, I. Starch Iodine Index Honeycrisp. 2012. Washington Tree Fruit Research Commission website. Available from: Starch Iodine Index HoneycrispAccessed Sept. 11, 2020)
  3. Rosend, J., et al., The effects of apple variety, ripening stage, and yeast strain on the volatile composition of apple cider. Heliyon, 2020. 5(6): p. e01953-e01953.
  4. Ewing, B., et al., Management of Apple Maturity and Postharvest Storage Conditions to Increase Polyphenols in Cider. HortScience, 2020. 54: p. 143-148.
  5. Peck, G. Harvest Maturity Resources. 2012. Available from: https://blogs.ext.vt.edu/tree-fruit-horticulture/2012/08/23/harvest-maturity-resources/. (Accessed Sept. 11, 2020)
  6. WSU Tree Fruit Comprehensive Tree Fruit Site, Washington State University. Apple Maturity and Harvest. 2017. Available from: http://treefruit.wsu.edu/web-article/harvest-apples/. (Accessed Sept. 11, 2020)