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University of Maryland Extension &
Department of Plant Science and Landscape Architecture, University of Maryland, College Park

Apple Maturity Assessments 2022: Red Delicious Week 9

On our ninth week of evaluating fruit apple maturity, we started evaluating Red Delicious fruits harvested from Federalsburg, MD. None of these fruits have received any plant growth regulator. Red Delicious fruits are ready to be harvested for mid to short-term storage, as they are displaying 65% of red coloration, firmness values ~16.5 lbs, flesh starch disappearance values of 3.5 as well as soluble solids contents of 12%. Red Delicious is a cultivar that presents high susceptibility to harvest drop, thus it is important to harvest at the right time to avoid further losses. We also observed presence of moldy core in this cultivar, as expected, due to its known susceptibility to it. The information is summarized in Table 1.



Surface color (eye-balling): Delicious fruits are presenting ~65% of red coloration.
Background color (DA index): Red Delicious fruit is presenting high values of ~1.6, typical of this cultivar. Readings of 0.6-0.7 are recommended for harvesting fruits for long-term storage, while an index of about 0.35 is targeted for harvesting fruit for short-term storage. Fruits were measured with a DA meter, a device that measures the absorbance difference between 670 nm and 720 nm light. A higher DA index indicates a larger content of chlorophyll-a in the fruit skin.


Fruit firmness: Red Delicious fruits are displaying firmness values of ~16.5lbs this week. In general, Red Delicious apples that are destined for long-term storage (>3 months) should be harvested with a firmness of at least 18lbs; while for fruit for mid- or shorter-term storage (1-2 months) a firmness of 16 - 17lbs is appropriate. Firmness was measured with a penetrometer with a 7/16-inch diameter plunger.


Starch content: Red Delicious fruits are displaying values of ~3.5. The common starch index rating system (Cornell chart) on a scale from 1 to 8, where 1 is full starch (all blue-black) and 8 is starch-free (no stain), was used. In general, on a 1 to 8 scale, values ranging from 3.5-5 are recommended for harvesting apples for storage, while 6-7 for fresh market.

Sugars and Acids

Soluble solids contents (SSC): SSC values, measured with a portable refractometer, are showing values of ~12.0% for Red Delicious. In general, it is recommended to harvest fruits with readings around 12% to 14% SSC.

Acidity Red Delicious acidity values are ~0.35, characteristic of this cultivar. A decrease in acidity content is an indicator of advancing maturity, reason why this indicator is included in this report. Acidity was measured with an automatic titrator, quantifying malic acid (the major acid present in the juice of apples).

Table 1. Table 1 Summary table of maturity assessments for Red Delicious harvested from Federalsburg, Maryland. 
Location Federalsburg, MD  
Cultivar Red Delicious  
Date 19 Sep  
Rootstock Unknown  
Diameter (in) 3.0  
Skin Red Color (% blush) 65  
DA Index 1.6  
Firmness (lbs) 16.5   
Starch Index (Cornell 1-8) 3.5  
Soluble Solids (%) 12.0  
Acidity (% Malic Acid) 0.35  

Fruit View

Federalsburg, MD
Red Delicious 


Meet the Team
Macarena Farcuh is an Assistant Professor of Horticulture in the Department of Plant Science and Landscape Architecture. She is interested in investigating how to develop novel strategies for improving fruit quality, nutritional value, shelf-life capacity, safety and marketability throughout fruit development, harvest and postharvest storage. Macarena’s research program integrates diverse approaches, including systems biology, physiology, biochemistry, analytical chemistry, molecular biology, and sensory science. Her goal is to contribute to decrease fruit loss/waste, support environmental sustainability and, at the same time, enhance fruit consumption by meeting consumers’ expectations and thus improve the health and well-being of populations.
Haley Sater is an agricultural extension agent for Wicomico County specializing in fruit and vegetable production. She is interested in connecting with produce growers across Maryland to identify and promote profitable and sustainable fruit and vegetable systems. Her background is in small fruits and plant breeding. 
Contact Us: Macarena Farcuh, Ph.D.
Assistant Professor and Extension Specialist
University of Maryland, College Park


Haley Sater Ph.D.
Wicomico County Extension Educator 
Wicomico County Extension Office
28647 Old Quantico Rd, Salisbury
The University of Maryland, College of Agriculture and Natural Resources programs are open to all and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, or national origin, marital status, genetic information, or political affiliation, or gender identity and expression.

Los programas del Colegio de Agricultura y Recursos Naturales de la Universidad de Maryland están abiertos a todos y no discriminará contra nadie debido a raza, edad, sexo, color, orientación sexual, discapacidad física o mental, religión, descendencia, origen nacional, estatus matrimonial, información genética, afiliación política, o identificación y expresión de género.

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