Photo courtesy of lef farms

Growing the highest-quality product is the first order of business in any greenhouse food production facility. However, what happens during the postharvest cold chain period is what will ensure the product will end up on the dinner table as fresh as the day it was picked. New methods for removing heat from produce and packaging is extending the shelf life of fresh greens and other produce.

Leading the way at lef Farms

lef Farms, a company that opened in 2016 in Loudon, N.H., is supplying fresh, hydroponically grown greens to an increasingly larger base of customers in New England. It is owned by Pleasant View Gardens, a company that has been selling ornamental plants for about 40 years. The company’s president and CEO, Henry Huntington, had been looking for a way to diversify when he went into the produce-growing business, says Bob LaDue, VP and COO, a former greenhouse consultant and Cornell-educated horticulturist. Instead of using existing facilities at Pleasant View, they constructed a 75,000-square-foot standalone growing facility with a cooler big enough to handle any future plans of expansion.

Now, lef Farms has found a way to approximately double the shelf life of its lettuce, Pak choi and other greens. This is allowing the company to expand its market to all of the New England states and New York, according to Donald “DJ” Grandmaison, sales and marketing manager at lef Farms.

LaDue and Huntington have examined the cold chain methods growers have used over the years. They have helped lef Farms come up with some innovations in chilling and packaging that LaDue says are “game-changer[s].”

Photo courtesy of lef farms

Photo courtesy of lef farms

Photo courtesy of lef Farms

“A lot of what I was seeing was people harvesting these products either in a greenhouse or head house at the temperature they were growing,” LaDue says. “Then [they were] putting it in a plastic bag or clam shell — some type of container — and then putting those in a box, sealing the box up, palletizing them, wrapping them up in shrink wrap and putting it in the cooler to cool off.” The product would then end up in a cooler waiting for pickup; the insulation in the packaging would do an effective, but unfortunately counterintuitive, job of trapping warm air inside the packaging.

“Some of my work at Cornell was to put temperature-recording devices inside the packaging, then pack them in the core of the pallet and put them in the cooler,” says LaDue, who managed a greenhouse growing operation at the university for 13 years. “We found out it could take several days for the products in the middle of the pallet to get cooled to the proper temperature. Meanwhile, you’ve lost a lot of shelf-life potential.”

LaDue says when the greens are cut in the dark, they still go through the process of respiration, consuming oxygen and releasing carbon dioxide. This normal cycle is what leads to eventual spoilage. This process can be slowed down by keeping the temperature cool around the product while still allowing respiration to take place.

“We want to keep that environment around the leaves balanced to a normal oxygen/carbon dioxide ratio,” LaDue says. “We looked at a lot of different options. Instead of packaging in the head house, we would conveyor the raw product into the cooler, cut it, mix it, weigh it, bag it and palletize it; it was quite different from anything that was being done anywhere worldwide.”

The company also looked at every aspect of the way the product was being packaged before it shipped. He said they worked with a packager to come up with a laser-perforated packaging that allows for this normal exchange of gases. They also box up the greens in boxes that are more open than traditional boxes. And instead of securing all of the boxes on the pallet with a thick shrink wrap, they use a thinner wrap that he says “spider webs” around the boxes, keeping them from falling off the pallet, but also allows for necessary air flow.

LaDue says the product takes about five minutes from the time it is cut until it is bagged and ready to ship. It is then moved on pallets into a sealed chamber and onto a truck, thus avoiding shocking the product.

“We’ve really gone a long way towards quickly and effectively getting rid of the heat from the crop, and it’s working really well,” he says. (Editor's note: Read more about the operation here)

Photo courtesy of lef Farms

Photo courtesy of lef Farms

Keeping it fresh at NatureFresh

NatureFresh Farms, purveyors of greenhouse bell peppers, cucumbers and tomatoes, has also made a sizable investment in a heat-reducing storage facility, in addition to technology to provide computerized labor management. These investments allow the company to manage both labor and cooling.

Founded in 1999, NatureFresh is a well-known grower in the industry who supplies fresh produce to all of Canada and as far south as Florida and Texas as well as the Central and Eastern U.S. Each year, they trial over 300 varieties of vegetables, selecting the ones they feel have the best flavor and shipping quality.

“All our commodities are consolidated within our new modern distribution center we officially opened in August 2017,” says Ray Wowryk, director of business development at NatureFresh, based in Leamington, Ontario, Canada. He says that the facility is equipped with advanced high-efficiency pre-coolers that remove heat prior to packaging or market distribution.

“Precooling is key to maximize shelf life,” Wowryk says. “Providing ideal storage commodity-specific temperature and humidity is key also.”

The company utilizes technology to monitor the state-of-the-art packaging and storage facilities they invested in.

“Adding modern equipment and updating packaging machines along the application and robotics improved overall efficiency and handling,” Wowryk says.

Monitoring of the product and surrounding environment doesn’t end when it leaves the distribution center. “There are a number of temperature monitors used for recording temperature during transportation,” Wowryk says. “Most retailers request specific brands supported by their food safety program. All provide the key data required to identify any breaks in the cold chain.”

Neil Moran is a horticulturist and freelance writer and copywriter for the green industry. greenindustrywriter.com

This article series is from the Resource Management in Commercial Greenhouse Production Multistate Research Project.

A renewed interest in urban and controlled environment agriculture (CEA) has come with the increased interest in locally and sustainably produced food. Consumers are more and more demanding that their produce be chemical-free, and they want to know where and how it was grown. Clearly, producing crops in urban environments has key benefits such as proximity to market, increased shelf life, and consumer knowledge about production practices. However, there are also major challenges such as the availability of suitable land that is free of hazardous materials, high property values and taxes, permits and regulations, finding skilled labor, and competition from cheaper field-grown products. The advantage of CEA is that most environmental conditions can be carefully controlled, which allows for year-round production and all but guarantees the highest potential yields. Typical growing structures range from high tunnels to greenhouses (Fig. 1), as well as re-purposed buildings (Fig. 2) or shipping containers (Fig. 3) that allow very little or no sunlight to reach the plants.

Depending on the latitude and the particular season, it is likely that electric lighting is needed to either supplement the naturally available sunlight for increased yields, to extend the day length, or to serve as the sole source of light. Since the human eye is not particularly good at assessing differences in light intensity and because humans can typically operate well in relatively low light intensities, we do not appreciate how much photosynthetic light plants need to grow and develop. In fact, plants need a lot more light than the average person would predict. Therefore, plant lighting is a critical component of urban crop production environments.

Types of supplemental lighting systems

Three different types of electric lamps are commonly used in CEA: fluorescent (FL), high-intensity discharge (HID) and light-emitting diodes (LEDs). HID lamps can be further divided into high-pressure sodium (HPS) and metal halide (MH) lamps. The FL and HID lamps come in different sizes and wattages, but once installed they produce light with a fixed color spectrum. On average, FL lamps convert approximately 20 percent of the supplied electric energy into photosynthetically active radiation (PAR; discussed below) that plants use for photosynthesis. They are often used in growth or germination chambers designed for seedling production or tissue culture. The conversion efficiency increases to around 30 percent for HID lamps. The color spectrum of the light produced by MH lamps contains a little more blue than HPS lamps, and they are most often used in garden centers so that plants appear more true to color. HPS lamps have an effective light spectrum to promote flowering of long-day plants and photosynthesis.

Recent technology advances have made high-intensity LED lamps more attractive as photosynthetic lighting sources: They can be designed to produce a specific color spectrum, or they allow for the spectrum to be adjusted based on the needs of the plant. Unlike HID lamps, LED lamps produce little radiant heat, so they can be placed much closer to the plant canopy without damaging leaf tissue (Fig. 4). However, LED lamps still produce (convective) heat that needs to be removed to ensure efficient operation and maximum lifespan. LED lamps specifically designed for plant growth applications have recently surpassed the conversion efficiency of double-ended HPS lamps and are expected to reach even higher conversion efficiencies in the future. Most high-intensity LED lamps for horticultural applications contain red and blue diodes and may contain white diodes to allow humans to see the true color of plants.

Supplemental lighting parameters

PAR refers to the waveband of light (between 400 to 700 nm) that is utilized by plants for photosynthesis. The amount of PAR a plant receives up to a species-specific level will increase photosynthetic rates and ultimately lead to improved growth, quality, and yield. Approximately 45 percent of the energy from the sun falls within the PAR waveband of 400 to 700 nm. Energy outside the PAR region is less photosynthetically active but may influence plant responses such as leaf/flower color (i.e., UV radiation can promote the concentration of anthocyanins), stem elongation (ratio of red:far-red light and blue radiation), flowering, and can also increase plant temperature (infrared radiation).

PAR is quantified in terms of instantaneous light intensity as the photosynthetic photon flux density (PPFD, units of µmol·m^-2·s^-1). Supplemental and sole-source light intensity guidelines vary by crop and by the amount of sunlight available. Generally, 50 to 90 µmol·m^-2·s^-1 of supplemental lighting from HPS lamps or LEDs are delivered to floriculture young plants and microgreens. Vegetables, herbs, and leafy greens are generally provided with higher supplemental lighting intensities of 100 to 200 µmol·m^-2·s^-1. Light intensities for indoor sole-source applications are often double or higher as those crops receive no sunlight.

The term daily light integral (DLI) is used to describe the cumulative amount of PAR that a square meter area receives over a 24-hour period. The unit for DLI is moles of PAR per square meter per day (mol·m^-2·d^-1). The target DLIs to produce acceptable quality floriculture and high-quality young plants is 10 to 12 mol·m^-2·d^-1 (Table 1). For most cut flowers and greenhouse vegetables, the minimum target DLI to produce an acceptable quality crops is 15 mol·m^-2·d-1. For fruiting vegetable crops increased DLI above 15 mol·m^-2·d^-1 will lead to increased crop yield. However, head lettuce is susceptible to the physiological disorder tip burn and becomes unmarketable when light levels exceed approximately 16-17 mol·m^-2·d^-1 (depending on cultivar and airflow).

For greenhouse production, there can be times when sunlight is excessive (e.g., resulting in tip burn in lettuce). For fruiting crops that can utilize higher DLIs, high amounts of sunlight may not be a problem but may make it difficult to control greenhouse temperature. Shading can be deployed all season long as a shading compound (ie., white wash) or a stationary net/screen, but the preferred method is a motorized retractable system that can be deployed automatically by the greenhouse environmental control computer when the light level exceeds a threshold value. Nighttime supplemental lighting of greenhouses can affect neighbors and thus be considered “light pollution” according to municipal code. Black out curtains can be used to mitigate such light pollution.

Lighting systems can be one of the highest capital costs in CEA. Growers are encouraged to work with a reputable horticultural lighting supplier to develop a lighting plan that will meet crop needs. Beyond the upfront cost and the energy efficacy (which determines the electricity cost) it is important to consider fixture shading and cooling, lifespan, warranty, maintenance and uniformity.

Some fixtures (i.e., FL and certain LED lamps) take up a large footprint for the amount of area they light, therefore these fixtures would provide excessive shade in a greenhouse environment and are better suited for sole source lighting applications. The lifespan of fixtures is usually rated based on the number of hours of operation to reach a certain decline in initial light output. For example, an L70 of 25,000 hours means that light output is expected to degrade to 70 percent of the original output after 25,000 hours of use. Depending on the crop and cost of electricity, it may be useful to replace a fixture or bulb even before the L70 is reached. Growers are encouraged to understand the warranty terms. Some fixtures are warranted for a given number of years and others based on the number of operating hours. Lighting suppliers can calculate a light map that displays the expected light intensity (PPFD) and uniformity at crop height given a particular layout of fixtures. Because lighting is such an important decision, get quotes from several suppliers and talk to colleagues for recommendations.

Finally, plant responses to light greatly depend on the crop being grown and specific environmental conditions (temperature, relative humidity, carbon dioxide concentration). Therefore, as with other production practices, it is highly recommended to conduct small-scale trials with lighting before considering large changes/investments.

A.J. is a professor and extension specialist at Rutgers University (both@sebs.rutgers.edu), Neil is an associate professor and extension specialist at Cornell University (neil.mattson@cornell.edu) and Roberto is an assistant professor and floriculture/controlled environment specialist at Michigan State University (rglopez@msu.edu). Acknowledgements. Financial support was received from the USDA National Institute of Food and Agriculture, Multistate Research Project NE-1335: Resource Management in Commercial Greenhouse Production.

I still remember a time when the only décor a chef would accouter his plates with was parsley — at least at the restaurants I went to. I hardly gave the little green sprig a second glance as I ate the rest of my meal. But there’s been a revolution over the years, with the little green “decorations” playing a more expansive role in the foods we eat. Recently, I went to a five-course tasting at a local restaurant with a stellar reputation, and my expectations were high.

Having never had this type of meal, I wasn’t sure what to expect. Fortunately, the waiter explained the types of dishes that the chef would be preparing and the order of the plates, so we knew more or less how it would go. As the dishes came out, I noticed that, regardless of whether it was pasta, fish, meat or dessert, there were colorful microgreens, herbs or both accompanying nearly every dish. And we ate every last one; each added a spark of flavor and complemented the other elements on the plate. For their size, they certainly packed quite the punch.

Rob Laing, CEO and founder of Farm.One, is well aware of the culinary power and popularity of these tiny plants. The vertical farm has grown 580 different varieties of rare herbs, edible flowers and microgreens in approximately 1,500 square feet of growing space across two locations in the heart of New York City. Chefs appreciate that they can get fresh herbs, edible flowers and microgreens delivered to their restaurants sometimes mere minutes after being harvested, and have a much wider selection than they would if they relied solely on seasonal items. This month, we’re sharing Farm.One's story.

Also in this issue, we have the second installment of the Urban Agriculture series, which focuses on lighting in vertical farms and greenhouses. Leslie Halleck shares her take on how to clearly communicate your production methods to your customers. If you’re interested in growing lettuce, don’t miss Christopher Currey’s Hydroponic Production Primer this month. We hear from growing media guru Brian Jackson of North Carolina State University in our article on wood fiber, and food safety expert Lisa Lupo on the Produce Safety Rule. We round out our issue with growers’ perspectives on maintaining the cold chain and the latest from The Produce Moms.

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