Post Harvest Vegetable Care on the Farm
From an article in Growing For Market by RonWhen we finally started our own mixed vegetable operation in a 77 acre ex-corn field, there were no trees, much less a walk-in cooler. We didn't think it would matter much. After all, our goal was to provide the freshest possible produce to our CSA members. We'd wake up early enough to harvest everything we planned on distributing that same day. What could be better than "just picked" greens, lettuce, tomatoes and squash?
It wasn't until some members started complaining that our mesclun seemed to go bad in their refrigerators faster than the week-old stuff from California that we began to look more closely at what we were doing. We realized that our responsibility to high quality vegetables didn't end once the product left out farm gate. Many of our customers were keeping our vegetables around for days (and even weeks) after we thought they would be consumed.
We learned that how we handle produce before, during and even minutes after harvesting makes a huge difference to the long term quality. Deterioration happens for a number of reasons including temperature, loss of water, physical damage, disease micro-organisms and even natural ripening processes. Now we try to take those factors into account even from the very start. Ironically it has, in most cases actually increased our harvest efficiency time-wise - and the increase in flavor and shelf-life for our customers definitely makes it more worth it.
In addition to giving out higher quality produce that will last longer in our customers' fridges, we can also now comfortably spread our harvest out over more days (meaning we can handle larger CSA distributions with less labor!)
Before the Harvest
Our post-harvest care actually starts a few days before our harvest with one thing we have (some) control over: water! We make sure that there is enough soil moisture before we harvest leafy greens and lettuce. Often this means irrigating before we harvest – but not right before we harvest, because we don't want to be picking wet leaves. We do the same thing with carrots – irrigating enough that we don't have to fork the carrots too much before they'll slide easily out of the soil, reducing physical stress on the carrots, and our backs.
For other crops like tomatoes and melons we take the opposite approach and reduce or stop watering altogether as we near harvest time to concentrate flavors. There's only so much we can reduce water on some heirloom melon varieties because harvests can be quite spread out, but that's definitely not the case with tomatoes! We grow our tomatoes in open sided high tunnels so we have perfect control over how much water they get which allows us to coordinate our pickings for peak flavor.
It's a surprisingly persistent myth that tomatoes ripen better on the vine than off. In fact, on hot days, tomatoes won't ripen as well or evenly on the vine as they do off. If you don't believe me, try a blind taste test with your customers! What does matter with flavor is how much water you've given your tomatoes the day or two before harvesting. We cut down our drip irrigation times 50 hours before picking and stop watering altogether 36 hours before harvesting – starting up again immediately after picking. If you've tasted the difference between tomatoes harvested just after a rain storm, versus after a few days of dry hot weather, you already know what a difference this can make. Although we grow several heirloom varieties each year, we've found we can impressively concentrate the flavor of our hybrids to the point that customers don't necessarily prefer heirlooms to hybrid varieties when given the choice.
In a complete turn-around from our earlier "just-picked" snobbery, we find that timing harvests based on weather and water actually leads to better long-term quality of our produce. For example, I'd rather harvest lettuce even three days early than during a rain that's predicted for our distribution day! Same with cilantro and other more delicate crops. Some varieties of Broccoli are especially susceptible to fungal disease from rain water sitting in the heads, but we really LIKE those varieties, so may harvest them days earlier than a distribution, too.
The most important thing to remember is that the quality of your produce is not going to improve once it's off the plant! Small indentations on tomatoes – or diseased spots on our Swiss Chard get worse looking every day. We cull poor quality produce in the field rather than having to sort through it up in the barn where it can make a whole tub look bad.
We fill tubs only loosely, rather than "packing them in" even if it means more trips in and out of the field, and we minimize stacking of crates in transport if we're worried that one might fall into another, bruising leaves. When we do find bruised leaves up at the barn, we pull them out immediately, BEFORE they go into the cooler.
I pick squash with jersey-cotton gloves, but my wife Kate has beautiful, soft womanly hands so she can pick 'em bare handed. We've seen what punctures and scratches can do to summer and winter squash over time – and we remind ourselves we aren't just picking for the quality over the 2 days before distribution, but for the next 10 days our customers might be keeping them in their refrigerator. Vegetables are never tossed into crates, and crates are never tossed down. If we have helpers, they are taught the importance of the "gentle touch" when they're grabbing produce.
Because we pick our tomatoes at "first blush" they get less bruised even if they get stacked a little high in the harvest containers. Still, we prefer not to let our hybrid tomatoes get stacked in the crates more than 2½ layers deep, and heirloom varieties are layered flat with nothing on top of them. We pick them into the same crates they'll be stored in to minimize handling damage.
For lettuce and leafy green crops we try to time harvests when it's cooler out. That used to mean harvesting early in the morning, but now we balance that with our concern over nitrate toxicity. Nitrates build up overnight in leafy vegetables - especially in the spring and fall here in the Northeast and it's advisable to pick after at least 4 hours of sunlight especially if it was cloudy the day before. That means we pick our greens and lettuce in the evening before a distribution if we can. Often we have too many hours of harvesting to do, so we have to pick in the day, but we bring down tubs of wet sheets that we drape over the crates while harvesting and stack the tubs in the shade of our harvest trailer. As the sun climbs higher, we take turns driving up to the cooler every 30 minutes to minimize the time the crops sit in the sun.
For crops that we will be water cooling with a hose, we make sure our harvest tubs have holes in the bottom to drain out the water.
Post-Harvest Temperature Control
The chart at the end of this article shows optimum storage temperatures for a selection of crops. Even if you can't reach the perfect temperatures, if you get nothing else out of reading this article, I hope it's how critically important it is to get crops down towards their optimal temperatures as soon as possible once they are off plant.
To use strawberries as an example, the ideal temperature to store them at is 32 F. Store them at 65 and you reduce their storage life by over 70%. That's depressing enough, but what's far worse is letting them sit at 77 deg F for just the few hours you might spend harvesting! Delay your cooling by only 4 hours from harvest and you reduce your storage time by almost half! Let them sit for 6-8 hours you're back down to 70% reduction in storage life even if you cool them down to 32 after that!
Also remember that the effects of temperature are additive. The most damage occurs immediately after harvest, because the crop is often even hotter than 77 degrees because it was sitting out in the sun. But even after you've cooled them down, they are going to heat up again at your farm stand, and then in your customers' cars on the way home. All those sub-optimal times add up together to destroy the quality of your produce, so it's essential that you control what you can control – especially in that first 30-60 minutes immediately after harvest!
In the case of especially sensitive crops like strawberries, it's also a question of marketability. We used to desperately rush around trying to line up customers for our flats of strawberries each spring before they went "gross". It was frustrating enough that we considered dropping the whole crop. Now we regularly sell 3-4 day old strawberries that look much better than the one day old strawberries we used to sell.
Some crops are "hydro-cooled" which for us means they are gently sprayed off with cold well-water. If you have helpers, it's really important to alert them to how much damage they can do directing a high pressure stream of water at your crops! Stronger crops like heartier Kale and collards, turnips, carrots, and beets might get sprayed down, but we don't do that for lighter greens, lettuce, basil, cilantro, or other crops that might hold the water, causing other types of decay problems.
Instead, we make sure they are packed lightly into harvest crates, and we spread the crates out only one layer deep on the cooler floor to maximize their access to the cold air. They stay like that for the 30 minutes it takes us to come up with the next trailer load of veggies – then they are stacked up or placed on wire mesh shelves and the new load of veggies are spread out on the cooler floor.
Whether you are hydro-cooling or air cooling, it's critical to get the core temperature of your produce down as quickly as possible to maintain quality and nutrition. As small growers we can learn a lot by looking at large agribusiness processing companies that process their crops right in the field with huge cooling, cleaning and processing rigs that move along with the pickers!
Walk-In Coolers Getting crops cooled down fast is something we can control, but for many small, diversified growers, we have to maintain our coolers at a compromise of temperatures. Trying to keep eggplants, peppers, lettuce and chard in the same cooler means you sort of have to pick a middling temperature or you'll end up with chilling injuries to sensitive crops (like cucumbers, peppers and eggplants) which can do lots of damage to your crop quality in a very short amount of time!
We started out with a home-built walk-in cooler and an Air Conditioner (and of course the CoolBot – but in one it's earlier incarnations!) set to a "compromise" temperature of 42-45 degrees. The CoolBot kept changing, but but the a/c unit and the Cooler never did. As the CoolBot improved over the years, we were able to more definitively set the temperature to what we wanted. We would lower the temperature more in the fall or early spring when we were picking cold-loving crops like strawberries, broccoli and cabbage, and raise it in the summer. We never put tomatoes in it. That system actually worked very well for us.
Now that we're larger, we've graduated to running two home-built coolers maintained at different temperatures (and of course still running on window air-conditioning units but now controlled by the commercially available "CoolBot" models we sell on at www.storeitcold.com.)
We store our tomatoes in the same tulip crates they were harvested in. They are kept between 58 and 70 degrees depending on how long we need them to last. Tomatoes stored below 55 degrees get mealy..
However you cool your product, it's important that the temperature they are stored at be consistent, to minimize the likelihood of condensation forming on the surface -reducing quality and providing another vector for disease organisms.
Post-Harvest Moisture/Humidity Control
As mentioned earlier, moisture control starts even before harvest with irrigation, but it doesn't end there. In our cooler right now, we have a ten pound bag of young summer squash loosely tied at the top. We packed them up for a local restaurant over two weeks ago and, they never came to pick them up. We intended to throw them out, but we didn't get around to it. That bag of squash is sitting just across the aisle from several shallow, ventilated crates of squash we picked just 4 days back. We intended to cover that squash with wet sheets because the crates allow air to come in on all four sides drying out the squash quite rapidly. What's interesting about this is that the 14 day old squash looks and feels much more fresh and "just picked" than the 2 day old squash!
Just a small percentage of water loss will reduce the quality and crunch of your produce. Even if you use a humidifier, the cold air in a cooler just can't hold as much water as warm air, and things are going to dry out. So (normally) when we pick into black tulip crates, we throw a wet sheet over the crates to keep things moist and spritz it regularly OR line the crates with plastic garbage bags that are open enough to allow air flow, but closed enough to keep more moisture in.
Many farmers use low-cost Rubbermaid crates that seal up tightly and do a great job keeping moisture in, but the complete lack of air and standing water that builds up at the bottom of the tubs creates dangerous conditions for bacteria and fungal growth. The tubs also break down in just a few seasons of sun exposure. It's more cost effective and safer to spend a bit more money on "real" harvest crates that will last for many years and are designed to maintain a good balance of moisture control and air-flow. That being said, I have to admit we still have an easy dozen Rubbermaid tubs still in regular use BUT I poked holes in the bottom and keep the tops off.
Products especially sensitive to water loss include: Apricots, Cantaloupe, Blackberries, Cherries, Broccolli, Chinese Vegetables, Bunched Greens, Grapes, Beets, Kohlrabi, Turnip, Mushrooms, Green Onions, Peaches, Mustard, Plums, Parsley, Raspberries, Radish, Strawberries, Spinach, Chard and Young Summer Squash. These are crops that it's especially important to keep in appropriate tubs, or covered in a wet sheet or you will quickly see a reduction in quality.
Communicating with your customers
Even if you are doing everything right, you also need to take the time to tell your customers what THEY should be doing to keep your produce fresh once they get it home. What's the point in taking all the care you do and then seeing someone pack their bags into a 100 degree car while they go off for an hour of U-Picking and then errands around town. We threaten our members with immediate expulsion from the CSA if they don't take veggies home and promptly place them in the fridge. We also explain the value of the "crisper" drawers in the fridges (higher humidity!) or tell them to keep things wrapped in (frequently washed) wet rags or partially closed plastic bags. Some of our CSA members swear by re-useable semi-breathable plastic produce bags, but we've never had a chance to try them.
When we started farming, the quality of produce available from our local big-box grocery store was pretty miserable. It wasn't that hard for us to compete. Just the fact that we offered local produce seemed to make people think we were heroes! But the same increased customer awareness and appreciation of "real food" that continues to drive more people to farmers' markets and CSA's around the country is impacting what we see selling in the grocery stores. Our local "Stop & Shop" now sells non-mealy and tasty heirloom tomatoes and disturbingly sweet organic carrots next to an impressive selection of gourmet and fingerling potatoes.
Linda Hildebrand, who started Food Bank Farm, was our "farm mentor" and among the many words of wisdom she imparted to us was that any individual customer will buy from us for a year or two because they appreciate our philosophy, personality – and often just because we're local! After that, we really need to be showing a solid difference in value from what they can get elsewhere or they'll drift away. A big part of that is remembering that it's not just how good the crop looks when they pick it up from the farm, but how it well it keeps until the days later that our customers actually consume it.
|Product||Temperature||Storage Life In Days|
|Broccoli, Cauliflower, Cabbage||32||10–14|
|Peas, fresh snap||32||7–10|
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