Post-Harvest Handling Decision Tool > Crop Groups > Baby Salad Greens
For the purpose of this study, salad greens includes the common mixed greens sold as “spring mix” or “mesclun,” as well as loose-leaf spinach and arugula. In general, the harvested leaves “fit on a fork,” (known at Rock Spring Farm by its acronym, FOAF) and are presented to customers as a ready-to-eat product, whether farms advertise it as such or not.
The primary considerations in the post-harvest handling of salad greens are the rapid cooling of the product and removing water from the surface of the leaves. Handling efficiency seems to be a function of personnel, with the size of washing tanks a minor consideration. The spinners used for drying can present a bottleneck in the operation.
Large, commercial operations utilize a wash line and conveyor belt system, moving the leaves through a series of wash tanks to cool the crop and remove grit. Visual inspection removes contaminants such as weeds or rotten leaves as the produce moves through the line.
On Upper Midwest market farms, the most common method for cooling and cleaning is to submerge the greens in a tank of water using a tray or bag, then to mix the different ingredients or do a final rinse in a larger tank. Most operations use a clothes washing machine set to the spin cycle to remove standing water from the leaves. The low level of mechanization means that the speed of the operation and the gentleness of the handling depend heavily on the speed and care of the personnel conducting it.
Many farms have moved away from the production of salad greens because prices have declined or failed to increase with the cost of production. Smaller CSA operations limited their offerings of salad greens, while mid-sized operations universally felt they could do better, but did not have much motivation to improve this area of production.
Bags and Trays for Initial Rinsing
On the surveyed farms, greens are harvested into a variety of containers, which determine the way in which the initial rinsing is managed.
At Rock Spring Farm, salad greens are harvested into wooden bushel crates lined with a mesh liner. Farmer Chris Blanchard notes that lining the crates isn’t very efficient, but he has the red mesh bags on hand and the wooden crates are the only harvest containers currently in use at Rock Spring Farm. After harvesting, the bags of greens are weighed and folder over at the top, then transported to the packing house. At the packing house, bags are dunked in a 100-gallon plastic tank, then palletized and put into the cooler until the packing crew is ready for the final rinse and mixing, which happens in a 300-gallon dairy bulk tank.
At Hog's Back Farm, greens are harvested into ventilated plastic totes. Greens are poured into 100-gallon tubs of water, then transferred into a second tank using a bulb tray, then removed into a hand-cranked salad spinner. Hog's Back Farm has moved to delivering salad greens only twice over the course of their summer shares.
Featherstone Farm forgoes the initial rinsing step, moving salad greens directly from harvest totes into large tanks of water.
At Driftless Organics, salad greens are washed using black bulb trays. Greens are placed in one tray, another tray placed on top of that, and the whole thing swished around in the tank to remove any field dirt. In cases of weedy crops or questionable quality, washed greens are sorted at a table by pouring from one tray into another and picking out the cull leaves and plants.
For mixing greens or washing bulk in large tanks, it is essential to handle the greens gently. At Rock Spring Farm, workers slide their hands into the tank of greens and use a circular motion underneath the greens to agitate and blend the leaves. The goal is to use the water instead of the hands to mix and move the product.
Spin Dry
To increase the storage life of baby salad greens, it is essential to remove almost all of the water from the surface of the leaves. All of the surveyed farms accomplish this by means of some sort of spinner.
The most common spinner on Midwest vegetable farms is used clothes washing machines. Only the spin cycle is used, typically for about forty-five seconds. The best practice is to monitor the outflow and turn off the spinner when water ceases flowing. With enamel paint on the exterior and an enameled or stainless steel basket, these have food-safe food contact surfaces.
Every grower visited uses mesh bags to hold the greens. These bags provide for ease and gentleness of transfer. About six pounds of greens are dried in each batch, usually in two bags to balance the machine.
Hog's Back Farm, which grows only two crops of salad greens each year, uses a five-gallon, hand-cranked Dynamic Salad Spinner. With a removable basket, this spinner can handle about three pounds of greens and takes about one minute to completely dry the greens. Rock Spring Farm used the same machine before upgrading to a washing machine.
Greens removed in mesh bags can be stockpiled to await spinning. According to growers, baby greens should not remain in the water for more than about twenty minutes.
For winter greens production, it is important to note that water frozen in the washing machine takes an extraordinarily long time to dry out. At Rock Spring Farm, the author was always grateful to have the Dynamic Salad Spinner as a backup device.
Overall washing speeds ranged from twenty to fifty pounds per labor hour.
Scale and Costs
The growers surveyed for this project all produced eighty to 100 pounds of salad mix each day that they packed it. The largest farms were packing salad mix up to four times each week, while the smallest packed it just one time each week.
None of the growers visited was entirely happy with their handling setup for salad mix.
The author used a hybrid system of Driftless-style bulb tray rinsing and bulk tank mixing on a farm where he worked in the mid-1990s. With this system he washed up to 200 pounds of salad mix in a day using a 400-gallon stainless steel bulk tank. At Rock Spring Farm, in the mid-2000s, 150 pounds of salad mix was washed daily. At larger volumes, speed and equipment remain the same, but greens are processed in multiple batches. Larger final wash tanks allow for more settling of sediment.
This information is part of a Post-harvest Handling Decision Tool developed by Chris Blanchard of Rock Spring Farm in Decorah, Iowa. The tool is a project of the Fruit and Vegetable Working Group affiliated with the Value Chain Partnerships program. This project was funded by the Iowa State University Extension Value Added Agriculture program and the Leopold Center for Sustainable Agriculture. Blanchard conducted case studies of three vegetable operations to gather information for this decision tool. Products referred to in this tool are not an endorsement by Iowa State University.