What I learned about peaches during my research career

Another crop our Postharvest Systems Team studied was peaches. Georgia is the Peach State. They still represent a major fruit crop in the state, but we no longer hold the distinction of the top producer. South Carolina claims that title. California produces prettier peaches than those on the East Coast. Our peaches have much better flavor. We attribute our predominance to the freestone varieties. California specializes in clingstones. The Team focused on following the peaches from orchard to market. My lab also studied quality of the fresh fruit.

My work with peaches date to my undergraduate days. I spent two summers working at Monarch Wine Company of Georgia. Our plant at Roberta processed peaches into concentrates and distilled spirits. Monarch produced cheap wines including its flagship brand, King Cotton Peach Wine. Peaches do not have as much sugar as grapes. Less sugars mean less alcohol. To reach the necessary level of alcohol, we needed to fortify it with distilled spirits (190 proof). To fortify peach wine, the winemaker must add spirits made from peaches. We made a low-alcohol peach wine and distilled off the alcohol. I was the QC guy for both operations. I conducted one quality test for my legal moonshine. I diluted the spirits: 1-part spirits and 2-parts distilled water. Then I took a swallow. If it burned on the way down, distillation was incomplete. No burning denoted top quality. I stored all my samples under lock and key. I was the only designated taster even though I was not old enough to buy a beer at a joint up the road.

author as a young man in his analytical laboratory
Measuring alcohol content of peach wine in my butcher coat

Those two summers provided me with great experience. I was the only person at the plant with a technical background, albeit as an undergrad. I was the first person in the position. I ordered all the equipment I needed to outfit my lab and designed all the quality tests. I relied on the help of Kell Heaton from the UGA station in Griffin! He was so patient, helpful, and kind. I remember the time I ordered lab coats for me and my assistant. I tried to explain to the laundry company representative what a lab coat looked like. We were not communicating until he had a burst of insight. “Oh, you mean a butcher coat!” He punctured my professional pride!

How can we tell if a peach is ripe? We worked with a packinghouse about 50 miles down the road. We needed a measure of maturity at harvest—a fancy way of how ripe a peach was when picked. Most peaches have a red side (blush color) and a green or yellow side (ground color). The amount of red varies by variety and predominates on the side of the peach facing the sun. Ground color turns from green to yellow as the fruit ripens. Researchers at Clemson developed a set of color chips ranging from light green to bright yellow. These chips helped us divide fruit into 6 categories of ripeness. Stage 1 was too green to ship. Stages 2-4 were acceptable for shipment. Stages 5-6 looked fine at the packinghouse. They would emerge as soft and juicy when they arrived at their destination up North. Upon arrival, juice would pour out of the truck onto the pavement if the shipment was too ripe.

Tracing a peach from orchard to market. Much like the work we did with tomatoes, we followed the peaches from the orchard to the packinghouse. Then we tracked them from the packinghouse to Georgia markets. We did not have the funds to send someone up to Cincinnati or wherever the fruit travelled. We ran tests to simulate truck time and temperature on the road. One limitation involved road vibrations. Types of fruits are susceptible to harmonic vibrations. Peaches bruise at a specific road speed, let’s say 45 mph. The peach faced double jeopardy. The vibration started at the surface into the flesh, bounced off the pit, and back to the surface.

tee-shirt for Dickey Farms, Growers and Shippers of Georgia Peaches Musella, GA
Packinghouse where I went to buy peaches

Meanwhile, back at the packinghouse. Peaches ride in open trailers from the orchard to the packing facility. The hot fruit is cooled with water soon after it arrives. Cold storage awaits the fruit until moving to the packing line. Brushes defuzz the rolling fruit, a physiologically incorrect step. Removing the fuzzy tricomes from the peach surface allows unwanted access to microbes. Consumers reject fuzzy peaches. Graders remove fruit from the belt that have defects, are too green, or too ripe. Locals rush to packinghouses to buy the over-ripe culls.

Unlike tomatoes, peaches develop some flavor as they ripen off the tree. Sugars increase to provide a sweeter fruit. As aromatics increase, the hard fruit begins to smell like a peach. We found that flavor developed when harvested at stage 3, but not so much for stage 2 fruit. Tomato flavor requires a combination of 32 or so compounds. Peach flavor is much simpler. One compound, gamma-decalactone, conveys a clear peach aroma. Other compounds are also important.  

What the consumer wants in a peach. To learn what consumers really want, we waded into the world of focus groups. The point of a focus group is to explore the range of responses. A group of 10-12 participants is not sufficient to represent all peach lovers. It provides a set number of potential market segments. Therese, the student conducting the focus groups, divided consumers into three segments:

A. the sweeter, the better,

B. tastes like a peach,

C. juice dribbles down the chin onto a waiting shirt 

The first two segments remind me of tomato preferences. Segment A focused on taste in the form of sugars. Segment B put more emphasis on the unique peach aroma. Segment C prioritized succulence. We also learned that there were differences in firmness that related to judging ripeness. Some participants sniffed their peaches to see if they were ripe. Others squeezed them. Squeezers deemed their peaches ripe if they gave slightly to the touch.

Technician using a drill press to measure peach firmness
Sue Ellen measuring peach firmness in the mobile lab

Please don’t squeeze our peaches. Next, we needed to verify our findings from the focus groups. Bob and I set out to three grocery stores each early on testing mornings. We needed twelve fresh peaches from each of three groups: firm-green, slight peach aroma, and slight softness. Produce managers were not happy seeing us squeeze and sniff their peaches before 9 o’clock! Ground color, the visible green-to-yellow part of the peach, was the best indicator of ripeness. Yellow indicated a peach that would ripen. Green was hopeless. The sniff test was a better indicator of edible quality than squeezing.

We took our show on the road presenting fruit to consumers at the Georgia Welcome Center, a strip mall in middle Georgia, and other commercial locations. For the best flavor, keep firm peaches refrigerated. Once removed from refrigeration, rapid softening occurs. Within about 8-12 hours the fruit will come to its flavorful, juiciest best. Left too long peaches become soft and mushy. WARNING: DON’T WEAR YOUR FAVORITE SHIRT!  

two people preparing score sheets for peach tests
Therese and Lary preparing for a consumer test

Let them know you are local. As with any fruit or vegetable, it is best to grow your own or live near to someone who does. A peach eaten soon after reaching peak ripeness on a tree is close to nirvana. Roadside stands in Georgia cater to out-of-state visitors. They display beautiful baskets of peaches at premium prices. Locals know to ask for fruit kept underneath the shelf. These peaches don’t look as appetizing, but they are juicy, full of flavor, and less expensive. Buy only a few as they will be past their prime soon.

Bottom line. A supermarket peach faces challenges to quality not encountered by one picked at peak ripeness off the tree. Variety and season also affect quality. Peach growers in middle Georgia and South Carolina dismay at the early peaches from north Florida and south Georgia. Consumers rush out to purchase the first peaches of the season only to be disappointed by the lack of flavor and juiciness. The later in the season, the better the fruit. Freestone varieties enter the market in early July with worse appearance but superior flavor to the clingstones that precede them. My mother-in-law bought only her favorite varieties from her trusted supplier. She knew her peaches. During peach season my group worked with a major supermarket chain to get direct, daily deliveries of local fruit into their stores. When it worked it was great, but there were problems. The produce managers needed enough peaches to keep their shelves stocked. Most growers or packers had trouble delivering on time to meet the grocery-store schedule.    

basket of fresh, whole mangoes
Mangoes courtesy of my next door neighbor

A note on mangoes. Therese also worked with mangoes. Both peaches and mangoes are stone fruits which ripen off the tree. Ripeness at harvest is critical to edible quality in both. Unlike peaches, mangoes undergo chilling injury. Never refrigerate them. Check them each day to see if they are softening. Prepare to eat them when they begin to soften and before they become mushy. Slice off a cheek and score it in a cross-hatched pattern. Flip the peel so the cubes stick out. Enjoy the fleshy treat. An imported mango will not provide the full flavor as one eaten off the tree. But mangoes allowed to ripen in the home are sure to please. The most popular variety in the US is ‘Tommy Atkins,’ known for its bright red peel. Its turpentine aroma and flavor are not representative of top-quality mangoes.

bottle of marinara sauce
Rao’s Homemade Marinara Sauce – good alternative when you can’t make your own Photo by Linn Steward

Breaking news. For a follow-up on the conversation between a cook and a food scientist, read about the cook’s favorite processed food.



Next week: Blueberries, sweet onions and other crops

Many thanks to Sue Ellen McCullough who was responsible for all the logistics associated with testing, Bob Flewellen, and Lary Hitchcock for technical support.,

to the students: Therese Malundo and Hrvoje Verzi

and my collaborators: Stan Prussia, Jeff Jordan, Bill Hurst, Chi Thai, Joe Garner, Elizabeth Baldwin, Anna Resurreccion, Stephen Myers, Stan Kays, and Glenn Ware.


6 thoughts on “What I learned about peaches during my research career

  1. “A supermarket peach faces challenges to quality not encountered by one picked at peak ripeness off the tree.” That’s a polite way of saying the best peaches are seasonal and local. One of these days I’m going to get to Georgia and experience the perfect peach first hand. I’m used to California peaches which are pretty good. But I gave up trying the peaches that make it to my local northeast markets and have been doing the best I can with local Hudson Valley peaches during their painfully short season.

    My special thanks to Professor Shewfelt for putting out my latest post. I’ve learned so much over the months we’ve been comparing notes. I could not have put it together the way I did had it not been for studying his books and engaging in our many discussions.


    1. Another way of thinking about supermarket peaches is that you can buy a good one if you know how to handle it. Getting a good supermarket tomato is much more difficult. With peaches don’t let the perfect be the enemy of the good!

      I hope other readers will check out your description of Rao’s. Our discussions have given me a deeper appreciation for the role of specific ingredients in cooking


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s