Checking apple maturity: What to look for

Follow these apple maturity guidelines to help target apple harvest at the optimum maturity and best storage life.

Maturity and storage guidelines by variety have been developed over the years through the Michigan State University Apple Maturity Program. These guidelines help target the harvest of apples at the optimum maturity and best storage life. Firmness and starch iodine index readings are easily performed in the field. Table 1 lists the suggested firmness and starch index levels for long-term and shorter-term storage by variety. The starch index "mature" level is a guide for long-term CA storage and the "over mature" level for short CA or cold storage.

Table 1. Suggested firmness and starch index levels for long-term and shorter-term storage by variety.

Variety

Firmness   (pounds)*

Starch   Index*

Short CA

Mid CA

Long CA

Export CA

Mature

Over mature

Braeburn

16

17

18


3

7

Cortland

14

15

16


4

6

Empire

14

15

16

18

3.5

6

Fuji

16

17

18


3

7

Gala

16

17

18


3

6

Golden Delicious

15

16

17


3

6.5

Honeycrisp

15

16

17


3.5

7

Idared

14

15

16


3.5

6

Jonagold

15

16

17


3.5

5.5

Jonathan

14

15

16


3.5

5.5

McIntosh

14

15

16


5

7

Mutsu/Crispin

16

17

18


3

6

Northern Spy

16

17

18


3

6

Red Delicious

16

17

18


2.5

5

Rome

15

16

18


3

5.5

Spartan

17

18

19


4

6

Winesap

17

18

19


2.5

6

*Firmness is measured with a mechanical 11-mm wide probe inserted into the pared flesh of a fruit to a distance of 8 mm. Starch index is measured on equatorial cross section of an apple stained with iodine solution and rated using the Cornell University starch-iodine index chart for apples on a 1-8 scale (Predicting Harvest Date Window for Apples by Blanpied and Silsbey, Cornell Extension Bulletin 221.)

Empire has a firmness level guideline for CA empires that are to be held for export. Empire needs an additional 2 pounds of firmness if they are to be exported. They need to be a minimum of 16 pounds firmness coming out of storage at shipping time to arrive at their export destination in good condition.

Starch iodine index indicates the gradual change of starch to sugars in the fruit. In general, immature fruit are nearly 100 percent full of starch and will stain black (1 or 2) on the 8 point New York Starch Iodine Index Chart. As the starch stain clears the core and starts to clear the flesh, the fruit then are mature and ideal for long-term CA storage. Fruits will often remain in the "mature" for seven to 10 days and then start to enter the "over mature" class. Over mature fruit are good for short CA or cold storage.

Brix readings are a guide for target sugar levels in fruit. The higher, the better, but from year to year there is quite a lot of variation. Light crops will tend to have higher brix levels and heavy crops will be on the low end. Honeycrisp are expected to have higher a brix.

Table 2. Brix readings on Honeycrisp and other varieties.

Brix Guide

Low

Fair

Good

Excellent

All Varieties

Less than 11

11

12

13

Honeycrisp

Less than 12

12

13

Greater than 14

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