Southwest Michigan apple maturity report – September 11, 2024

Apple harvesting in southwest Michigan is moving rapidly.

Cross-sections of apples that have been stained blue.
Cross section of fuji apples with starch staining blue with iodine. The center core regions no longer stain blue because the starch has converted to sugar, indicating the apples are nearly mature. Photo by Diedrie Hulshof.

This is our weekly southwest region apple maturity report. Reports are sent out following the Michigan State University Extension fruit team apple maturity calls on Wednesday morning. View Michigan State University Extension’s Apple Maturity page for regional reports throughout the state and additional resources.

Overview for this week

Picking has focused on harvesting of Jonagold and Honeycrisp over the past week in central Berrien County. More moderate temperatures over the past week slowed apple maturation.

Honeycrisp 

Internal starch conversion for this variety for the last three weeks averaged 5, 6.8 and now 7.3, very mature. The mature starch threshold is 3.5. Fruit are internally mature. The current average firmness reading is 13.5, below the recommended firmness for short-term controlled atmosphere (CA) storage (15 lbs). The predicted peak harvest date for central Berrien County is Aug. 29. Refer to this article by MSU researcher Randy Beaudry on Honeycrisp harvest and storage recommendations. As of early this week, about half of the area Honeycrisp orchards remained to be harvested or finished harvesting. 

Collection Date 

Red Color (%) 

Firmness (lbs) 

Starch (1-8) 

Soluble Solids (Brix) 

Aug. 19 

48.0 (45-55) 

15.7 (14.3-16.4) 

1.9 (1.4-2.8) 

10.8 (10.3-11.4) 

Aug. 26 

56.6 (35-67.5) 

14.9 (14.2-15.6) 

5 (4.2-6.0) 

11.6 (11.1-12.1) 

Sep. 3 

60 (55-72.5) 

13.7 (12.7-15) 

6.8 (5-7.4) 

13 (12.6-13.5) 

Sep. 10 

70 (60-75) 

13.5 (12.3-14.4) 

7.3 (7-7.6) 

13 (11.3-15) 

*Starch values according to the 1-8 scale developed by Cornell University. 

Empire 

This variety is averaging 4 for the starch test—the mature starch threshold is 3.5. The current average firmness reading is 17.3 lbs, about the same as last week, still close to the desired minimum firmness for long-term CA storage of 16 lbs. The predicted peak harvest date for central Berrien County for fresh market CA storage is Sept. 7, which still is on target. Approximately half of the area Empire remain to be harvested.  

Collection Date 

Red Color (%) 

Firmness (lbs) 

Starch (1-8) 

Soluble Solids (Brix) 

Aug. 26 

59.3 (40-89) 

18.3 (17.4-19.7) 

2.2 (1.6-3.0) 

11.0 (9.9-12.3) 

Sep. 3 

75 (55-97.5) 

17.3 (16.6-17.6) 

3.5 (2.6-4.2) 

11.3 (20.8-12.4) 

Sep. 9 

87 (72-97) 

17.3 (15-17.9) 

4 (2.8-4.8) 

11.4 (10.8-12.6) 

*Starch values according to the 1-8 scale developed by Cornell University. 

Golden Delicious 

This variety is averaging 3.1 for the starch test, considered mature—the mature starch threshold for fresh market is 3. The current average firmness reading is 16.7 lbs, about the same as last week, the desired minimum firmness for long-term CA storage is 17 lbs. This variety is ripening close to the predicted peak harvest date of Sept. 13 for central Berrien County. Picking has not started in most Golden Delicious orchards in central Berrien County. 

Collection Date 

Red Color (%) 

Firmness (lbs) 

Starch (1-8) 

Soluble Solids (Brix) 

Sep. 3 

35.9 (20-30) 

16.7 (15.8-18.2) 

2.6 (1.6-3.2) 

11.5 (10.7-12.3) 

Sep. 9 

30 (20-40) 

16.7 (15.4-18.4) 

3.1 (2.2-3.6) 

12.2 (11.7-12.5) 

*Starch values according to the 1-8 scale developed by Cornell University. 

Jonagold 

This variety is averaging 4.9 for the starch test, a jump from last week’s 2.6 reading—the mature starch threshold for fresh market is 3.5. The current average firmness reading is 17.3 lbs, the desired minimum firmness for long-term CA storage is 17 lbs. The predicted peak harvest date for central Berrien County is Sept. 10. Most area Jonagold orchards have been picked or are in the process of being picked.  

Collection Date 

Red Color (%) 

Firmness (lbs) 

Starch (1-8) 

Soluble Solids (Brix) 

Sep. 3 

62.6 (37.5-89) 

19.4 (16.4-22) 

2.6 (2-4) 

12.3 (11.4-13.4) 

Sep. 9 

74 (50-96) 

17.3 (16.2-20) 

4.9 (3.4-6.6) 

13 (12.1-15.6) 

*Starch values according to the 1-8 scale developed by Cornell University. 

Red Delicious 

This variety was sampled for the first time this week. This variety is averaging 2.8 for the starch test—the mature starch threshold for fresh market is 2.5. The current average firmness reading is 17.9 lbs—the desired minimum firmness for long-term CA storage is 18 lbs. This variety is maturing slightly ahead of the predicted peak harvest date of Sept. 17 for Red Delicious in central Berrien County. Picking has not started in most Red Delicious orchards in central Berrien County.  

Collection Date 

Red Color (%) 

Firmness (lbs) 

Starch (1-8) 

Soluble Solids (Brix) 

Sep. 9 

99 (96-100) 

17.9 (17.3-19) 

2.8 (2-3.2) 

10.3 (9.7-11.1) 

*Starch values according to the 1-8 scale developed by Cornell University. 

Fuji (main season) 

This variety is averaging 2.8 for the starch test—the mature starch threshold for fresh market is 3. The current average firmness reading is 19.1 lbs, the desired minimum firmness for long-term CA storage is 18 lbs. The predicted peak harvest date for central Berrien County is Sept. 13, which seems to be on target. Picking can be delayed waiting for better size, blush and brix. Picking has not started in Berrien County area Fuji orchards. 

Collection Date 

Red Color (%) 

Firmness (lbs) 

Starch (1-8) 

Soluble Solids (Brix) 

Sep. 9 

51 (40-72) 

19.1 (17.7-21.5) 

2.8 (2-3) 

11.5 (9.9-13.2) 

*Starch values according to the 1-8 scale developed by Cornell University. 

Apple maturity sampling parameters

  • Color % = the visual percentage of red color (blush) from 0 to 100; range shown is for the orchard averages.
  • Firmness in lbs pressure, skin off, as measured with a FT Penetrometer; range is for the site averages.
  • Starch: 1 = all starch (solid blue staining), 8 = no starch (white); range is for the site averages. Starch Iodine Index Chart.
  • Brix = % sugar measured with Atago PAL-1 Pocket Refractometer

Suggested firmness and starch index levels for long-term and shorter-term controlled atmosphere (CA) storage by variety.

Variety

Firmness (lbs)*

Starch Index*

Short CA

Mid-CA

Long CA

Mature

Over mature

McIntosh

14

15

16

5

7

Gala

16

17

18

3

6

Honeycrisp

15

16

17

3.5

7

Empire

14

15

16

3.5

6

Early Fuji

16

17

18

3

7

Jonagold

15

16

17

3.5

5.5

Jonathan

14

15

16

3.5

5.5

Golden Delicious

15

16

17

3

6.5

Red Delicious

16

17

18

2.5

6

Idared

14

15

16

3.5

6

Fuji

16

17

18

3

7

Rome

15

16

18

3

5.5

Braeburn

16

17

18

2.5

7

See the following helpful resources for more information:

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