When you think of fresh fruit, your mind may picture farms in the countryside. But local non-profit Concrete Jungle, whose team focuses on collecting neglected ripe fruits, vegetables and nut trees around the city to serve the hungry, is trying to change that. Since 2009 they have harvested thousands of fruit and nut trees in Atlanta’s public parks, backyards, abandoned industrial buildings, and even on interstate ramps.
“Our goal is to increase fresh food access to food-insecure groups throughout the Atlanta area, but we like to keep things interesting, so its important to us to keep our events fun and/or unusual,” says co-founder Craig Durkin. They also have an urban farm in Southwest Atlanta farm, from which they harvest and donate vegetables.
The non-profit not only wanted to collect produce when they find it, but track and document the most fruitful (pun intended) spots around Atlanta. They have documented over 2,800 fruit trees so far of over 20 different varieties on an interactive food map. As their urban harvest grew, one of the biggest challenges the team encountered was keeping track of the varying fruit tree production and monitoring when the ideal time is for the perfect ripe fruit.
Durkin, along with co-founder Aubrey Daniels and director Katherine Kennedy, reached out to Georgia Tech’s School of Digital Media for help solving this problem — how to remotely access thousands of trees and sense when fruit is ready to pick. Carl DiSalvo’s Public Design Workshop research studio at Georgia Tech specializes on experimenting with different avenues of design. The combined team of academics, agricultural specialists, and social good leaders came up with an array of ideas to detect ripe fruit, from drones and mechanical sensors to embedded tree cameras or even using old-fashioned human sensors (passersby) .
“One of the ways we’re pursuing is trying to smell gases given off by fruits as they ripen. The most common gas is known as ethylene, but many other are present as well. Ethylene is the reason you can ripen tomatoes by putting them in a bag with a banana. It acts as both a sign that the fruit as ripening, and as a signal to other fruit to induce ripening,” says Durkin.
While the ethylene sensor is too large (and expensive) 
for 2,000+ trees, the organization has been trying out cheap off-the-shelf gas sensors as an interim method. They detect several types of combustible gas including natural gas, propane, alcohol and hydrogen.
“We’re utilizing the sensors’ cheapness to our advantage — a $2 hydrogen sensor is likely going to have some cross-sensitivity with other gases and we’re hoping that by using enough of these cheap sensors we can pick up some meaningful signal,” says Durkin.
While the process is quite finicky, according to Durkin, the group has been able to get good results with persimmon trees and positive signs for apples; they are still working toward picking up pears with the sensors. For those, Concrete Jungle hopes to experiment with mechanical sensors — there is a slight noticeable change in the branch’s angle when a pear is ready to be picked, though weather could get in the way.
Durkin hopes that food technology continues to evolve and help them create better hardware for the sensors.
“We’re hoping that we can come up with something relating to fruit sensing, but in general, smell is an underutilized means of detecting things, in part because the good instruments are very expensive,” says Durkin. “Our goal is to at least contribute towards making these cheaper sensors more useable by improving the electronics and software tooling around them. Our partner in Denmark uses these sensors for process control at breweries and biogas plants, distinguishing between different types of spices and herbs, and drug sniffing.”
Photos provided by Concrete Jungle. Tree sensor photo via Sean Mackey.
