Sweet science: Precision apple harvesting

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Apple producers in Canada face various challenges throughout the growing season. One of these challenges is being able to predict exactly when crops are ready for harvest.

Fortunately, Canadian apple producers have science on their team. Agriculture and Agri-Food Canada (AAFC) researchers in Summerland, British Columbia, and Kentville, Nova Scotia, are creating protocols for using the DA Meter, a new tool that takes the guesswork out of apple harvesting. (DA stands for "delta absorbance"; it refers to a calculation of the difference in light that is absorbed by the chlorophyll in the fruit's peel as it matures.) This special tool helps fruit producers determine optimal ripeness of their crop which, in turn, helps ensure only the best apples make it to market.

"You can't judge an apple by its looks. That's why we use an instrument like the DA Meter to help us know what's going on inside the apple. This tool could change how and when Canadian apple growers harvest their crops."

- Dr. Peter Toivonen, Research Scientist, Agriculture and Agri-Food Canada

A new way to measure ripeness

When it first came on the market, the DA Meter was not well adapted to reading apple ripeness. Dr. Toivonen's team found that adding a light shroud helped generate consistent readings. This simple, yet effective, modification made it possible to collect the data needed to develop harvesting protocols for growers.

Typically, to measure apple ripeness, producers test the fruit for its starch content. They pick the apples, cut them open, and spray them with iodine. The iodine reacts with the starch in the fruit and turns black. When an apple is ripe, it has very little starch and the iodine creates only a light stain.

Precision agriculture

The iodine test is a visual indication of ripeness. Unfortunately, this technique is imprecise and the grower loses fruit with every test.

The DA Meter has LEDs on the outside of the sensor. When the light from the LEDs shines on the apple, it goes into the fruit and gets reflected back. The instrument reads the light reflection to measure the chlorophyll content of the apple's peel without damaging the fruit.

Using the DA Meter is a real advancement in maturity testing. Growers can test the apples right on the tree and leave them on the tree to continue to ripen. Picking the fruit when it's at the correct maturity is very important in keeping their quality high throughout the storage season.

Growers can also determine which parts of the field are ripening ahead of other parts, which helps them more effectively plan their harvest schedule. Since the tests don't destroy the fruit, they can do a lot more testing to ensure top quality.

Key facts

  • Researchers in Summerland are working on protocols for the Ambrosia, Golden Delicious, Gala, Fuji, Salish and Aurora Golden Gala, as well as several yet unnamed cultivars. In Kentville, researchers are working on protocols for the Honeycrisp.
  • Protocol data will be released to apple grower associations for new varieties as they become available.
  • In a three-year study using Ambrosia apples, data generated by the DA meter was a more reliable indicator of harvest maturity than traditional testing. The data is also useful in predicting how well apples will retain their firmness in storage.
  • In 2014, Canada's apple crop had a farm gate value of nearly $188 million. The top three apple-producing provinces were Ontario ($71.3 million), Quebec ($50.4 million) and British Columbia ($47.6 million).

Photo gallery

Dr. Peter Toivonen
Using the new techniques developed by AAFC researchers, apple growers can test their fruit as many times as they like, right on the tree, and determine the perfect time to harvest their crop.
iodine reacts with the starch in the apple and turns black
As an apple ripens, starch is metabolized into sugars and the apple gets sweeter. The apples in the upper middle of the photo reacted strongly to the iodine test because they're still very starchy. The apple on the right is riper, which lessened the iodine's reaction.
Ambrosia apples
Picking apples like these Ambrosia™, above, when they're at optimal ripeness will help ensure only the highest quality apples make it to market.

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