Assessing Apple Fruit Maturity in 2016—a Multi-State Outreach Project Supported by Grower Funding

Posted: July 29, 2016

Routine assessments of fruit starch levels, ground color and other maturity indices allow growers to make improved decisions about optimum harvest dates for long-term storage. During August through the end of October, 2016, Fruit Times subscribers will receive weekly summaries on changes in fruit maturity and will also be directed to more comprehensive information at the Penn State Fruit Research and Extension Center Seasonal Update site.
Blush and ground color changes as fruit mature. Photo: C. Walsh.

Blush and ground color changes as fruit mature. Photo: C. Walsh.

The Mid-Atlantic apple industry is going through a number of dramatic changes due to the planting of high density orchards with newer cultivars. These transitions, coupled with climate and weather changes, make it difficult for growers to predict optimum fruit maturity for long-term storage.

To track developments in physiological maturity, we will measure starch pattern, firmness, soluble solids, fruit size, % red color and ground color changes (visually and with a Delta A meter). The cumulative data will be updated weekly at Apple Maturity Assessments, and summaries of Starch Pattern Index and Delta A values will be posted weekly at Fruit Times. The starch index measures the loss of starch in the flesh, while Delta A values quantify changes in ground color. These two indices are relatively easy to monitor in the laboratory and can be used for judging apple fruit maturity in a range of apple cultivars.

Five cultivars will be included in the project. Brookfield Gala, Crimson Crisp, Aztec Fuji and Cripps Pink will be harvested from research plots at the University of Maryland Farm in Keedysville, Maryland, while Premier Honeycrisp and Honeycrisp will be harvested from a commercial Adams County, Pennsylvania orchard.

Our working hypothesis is that ethylene—sometimes referred to as the fruit ripening hormone—increases as fruit mature, leading to the coordinated ripening of apples. Ethylene initiates new enzyme production in fruit that affects visible attributes like surface color and ground color, as well as hidden attributes like starch pattern index, flesh firmness and soluble solids.

The project is supported by the State Horticultural Association of Pennsylvania Research Committee and is a cooperative effort of University of Maryland Extension and Penn State Extension.

Subscribers to the electronic version of Fruit Times will receive the weekly reports by emails easily read on a smart phone. If you receive the paper copy of Fruit Times, visit your library for the weekly updates that will be posted at Penn State Extension Tree Fruit Production. To sign up for electronic updates, visit Subscribe to Our Email List.

Contact Information

Christopher S. Walsh
  • Professor of Pomology, University of Maryland
Tara Baugher
  • Extension Educator, Tree Fruit
Phone: 717-334-6271 x314