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Post-Harvest Storage Tips

Posted by Zack Foust, Sales Representative on 9/16/2018

After hours of seeding, moving hundreds of transplants, mixing fresh batches of nutrients and managing a plant-friendly environment, you hopefully have produced a bountiful, disease-free crop that is ready for harvest. The next critical step in fresh-market hydroponic production is to follow proper harvest and storage practices to ensure that your customers receive produce of the highest quality. It is important that you don't overlook post-harvest care, since this could determine taste, texture, nutrition, safety and overall salability of your produce.

Lettuce
Every crop has different post-harvest techniques that should be followed to maintain the most desireable produce. Lettuce harvesting is fairly straight forward. The whole head should be harvested and the roots should be left intact to maximize life in storage, which can range from 2-3 weeks. Roots can get very long in most cases, so they should be trimmed down to a manageable size prior to storage. If you choose to remove the roots, a sanitized knife should be used to separate the roots from the head and the head should be stored as quickly as possible to slow the process of decay. Without attached roots, the shelf life can be between 3-5 days for Bibb varieties or 7-10 days for romaine varieties.

There are a few different methods that growers employ to store lettuce after harvest. If the lettuce is going to packaged for bulk sale, line a corrugated cardboard box with a food-safe plastic liner to separate the heads from the cardboard. Make sure the liner also covers the heads on top once the box is full. If the lettuce will be packaged for retail sale, it is common for growers to store individual heads in hinged plastic crispers or clamshells. Some crispers have a spot for roots to be stored while other are completely flat. Size and shape ultimately depend on the customers' needs, but storage principles are the same.

It is important to quickly store the box of crispers in a cooler that is set at a near-freezing temperature, 34-40oF. If the temperature drops below freezing, the water within the plant cells can freeze. These ice crystals expand, and because the cell walls rupture, the lettuce will have a watery appearance. If allowed to thaw, the lettuce will quickly decay. Plastic liners for bulk packaging and clamshells for retail are important because they keep the relative humidity very high (95-100%), which can slow the process of water loss from the heads.

Tomatoes
Tomatoes are harvested, packaged and stored differently than lettuce, but some factors can also differ between different types of tomatoes. For this discussion, we will focus on beefsteak tomatoes. Depending on who the grower sells to and how long they must be stored, tomatoes may be harvested when  the blossom end first begins to turn pink or when the tomatoes are fully ripe on the vine. In either case, once the tomato is picked you may choose to remove or leave the calyx (stem). If removed, the scar makes the tomato more susceptible to rot, but reduces the risk of the calyx causing physical damage by punching the skin of nearby tomatoes.

Once the fate of the calyx is decided, the tomatoes are often stored in a corrugated cardboard box labelled for greenhouse tomatoes. The boxes are often labelled for the total weight of the contents, so choose a box suited to your customers' needs. The full boxes are then stored in a room or a cooler set to a temperature based on the level of ripeness of the tomatoes. For tomatoes that are not fully ripe, the optimum temperature range is between 58-60 oF, however a minumum temperature of 50 oF  must be maintained to avoid chilling injury and a maximum of 70 oF  to avoide heat damage. All tomatoes require 85-95% relative humidity for optimum storage.

The storage life of tomatoes greatly depends on how ripe the fruits are and the temperature at which they are stored. For mature, green tomatoes, they can be stored for about 21-28 days, partially ripe tomatoes can be stored for about 7-14 days, and fully ripe fruits can be stored for about 2-4 days. Fully ripe tomatoes can be stored between 45-50 oF  to extend shelf life. The actual shelf life of a tomato will depend on temperature, humidity, gases present and ripeness.

Cucumbers
Cucumbers are different than both lettuce and tomatoes; they should be harvested and stored based on size, variety and intended use. Pickling and snack varieties should be harvested between 2-6" long while European and slicing varieties should be harvested between 6-10" long. A common rule of thumb: when the flower falls off the blossom end, the fruit is fully mature. Harvest the cucumber by cutting the stem about 1/4" above the fruit, using a sanitized tool. The harvested cucumbers must be stored in a cooler with a temperature between 45-50 oF  and a relative humidity between 95-100%. There should be no ethylene-generating produce stored in the same cooler as cucumbers or else they can quickly turn yellow. Cucumbers have a shelf life between 7-14 days if they are stored under the optimum conditions. Wrapping individual cucumbers in shrink wrap also prevents excess water loss and can keep the fruit from becoming rubbery in texture.

Lettuce, tomatoes and cucumber are crops that are very common in hydroponic greenhouse operations, however there are many more crops with different harvest and storage requirements. A very brief summary of the requirements we discussed can be found in the table below. If you have questions, please feel free to contact us here at CropKing and one of our staff members will be glad to assist you!

 

Optimum Temp (oF) Range

Relative Humidity (%)

Shelf Life (days)

Lettuce

34-40

95-100

With Roots

Without Roots

21-35

3-10

Tomatoes

58-60

85-95

Mature, Green Skin

Mature, Some Color

Fully Ripe

21-28

7-14

2-4

Cucumbers

45-50

95-100

7-14


 

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