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New Trick for Picking a Perfectly Ripe Fruit

Timothy Boyer Ph.D.'s picture
New test accurately determines ripeness in fruit

Do you avoid buying many fruits because you just can’t seem to pick one that is perfectly ripe? A new study suggests that all of this may change with an electronic tapping trick for picking a perfectly ripe fruit.


Food Shopping Hurdle

The biggest frustration with shopping for food is discovering that after arriving home, a bag of oranges, avocadoes, kiwis, melons or whatever you bought, literally and metaphorically brings a bad taste to your mouth. Especially when you consider yourself to be fairly adept at picking ripe fruit.

Unfortunately, there are a number of reasons why fruit just doesn’t taste the same anymore. Aside from the common knowledge that many fruits come from overseas, are picked well before they have ripened and subsequently have been chemically treated to induce ripening, one of the hard truths is that many fruits are selected for their appearance because appearance sells. And by appearance, we are talking about its size, its coloration, and other qualities that tempt shoppers into making a purchase. Flavor is secondary when it comes to profit.

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Using the Senses to Test for Ripeness

So, we do what we can to test fruit for ripeness with all sorts of thumping, eyeballing, squeezing and sniffing tests. I had an aunt Olga who was fearless in taking a bite out of produce while she shopped. As horrifying as that seems with respect to unwashed fruit coated with pesticide residue and bacteria from the hands of the grocer, she managed to live to be 105 and probably enjoyed only the ripest of fruit all the time.

One of my favorite tricks that I like to convince myself (and other shoppers) that I know what I am doing is the fingernail pop test with watermelons. Essentially, I press a fingernail against the watermelon skin and if I hear and feel a pop, I deem it likely to be ready to eat. No watermelon thumping for me—that’s for rubes.

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My point is that for all of us who are in charge of shopping for food to feed our families is that we all have our peculiarities that are based more on myth than on science. But that may change soon.

Scientific Test for Ripeness

According to a new study published in the journal Biosystems Engineering, researchers from Cranfield University have discovered that there’s a technological solution to the problem using a laser and a small vibration detector that can test an individual fruits’ resonant frequency, which thereby provides a reliable assessment of ripeness—and, without damaging the fruit!

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A news release from Cranfield University tells us that up to 30% of avocado fruit are currently wasted due to damage caused by testing during grading, with a further 5% loss at retail. Much like a prodding or squeezing by hand, an automated manual method is the current test where a pneumatic device pushes directly into the fruit and thereby too often damages the fruit.

Researchers found that a less damaging and more accurate testing method is to use Laser Doppler Vibrometry (LDV). The LDV beams a laser at the fruit to measure refracted light and then uses small vibrations caused by a simple automated impact device which taps the fruit to determine the fruit’s resonant frequency. As it turns out, the LDV test was proven to accurately predict the ready-to-eat ripened stage of avocado fruit.

According to the news release, scientists believe that this is a novel testing approach that can save money and reduce waste:

“Hard fruits create a higher frequency than soft fruits, so we calculated the perfect frequency for a ripe avocado and accurately measured this with the LDV test. Leaving the fruit undamaged is of great benefit and vastly reduces waste. The test we have developed could be extended to other fruits,” says Professor Leon Terry, Director of Environment and Agrifood at Cranfield University.

Research Fellow Dr. Sandra Landahl who co-authored the study added: “We tested the accuracy of LDV on a real factory line, under lab conditions, and the method has real potential, giving accurate measures of ripeness without damaging fruit. If developed, a simple ‘traffic light’ system could sort the fruit into those that are ripe, for discard or for storage, helping industry tackle food waste at this point in the supply chain.”

The plus for shoppers and gardeners is that rather than having to rely on some rather speculative traditional testing methods, it’s not a too far-fetched notion that someone will soon adopt the researcher’s strategy and design a simple handheld device to take the guesswork out of picking fruit when its ripest whether from produce the bin or the garden.

Turn Your Gardening Skills into a Gift to the Next Generation

If you have a favorite ripeness testing method, please tell us in the comments section below what test you use on which fruit and how well it works for you.

Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Today, with a background in farming and an avid home gardener, Timothy continues writing about science with a focus on the connection between plant biology and gardening for healthy living. For continual updates about plants and health, you can also follow Timothy on Twitter at TimBoyerWrites.

Image courtesy of Pixabay


New test could guarantee the perfect avocado” Cranfield University, 5 May 2020.

Non-destructive discrimination of avocado fruit ripeness using laser Doppler vibrometry” Sandra Landahl and Leon A. Terry; Biosystems Engineering, Volume 194, June 2020, Pages 251-260; https://doi.org/10.1016/j.biosystemseng.2020.04.001