Crop Production: Post-Harvest

After Harvest Care and Handling of Crops: Raking in the Profits

At the end of the season, there is relief in sight and the promise of a reward for the hard work and care given to a crop. If crops are not handled properly all the hard work put into growing the crop will be in vain. Improper storage and handling of horticultural crops can lead to major loss in product and yields. Understanding the science of handling crops will assist in making sure that storage and handling goes as smooth as possible. Overall the post-harvest handling of crops determines the overall quality of the crop regardless of whether the crop is sold fresh or processed. 

During post harvest there are many aspects that need to be followed and anticipated before the harvest of the crop. These are cooling, cleaning, sorting and packing, and overall safe handling of the crops. However, before tackling the proper handling of the final product, a grower needs to be aware of overall goals of post harvest. One of the most important goals of post harvest is keeping the product cool to help avoid moisture loss as well as, slow down chemical changes and physical damages.

Sanitation and cleanliness is another huge factor in post harvest quality. Proper sanitation reduces the possibility of pathogens that could be carried and destroy fresh produce. In some operations where there is an open field, many of these processes occur out in open meaning that sanitation and cleanliness are even more essential to reduce the risk of contamination like that from unclean rinse water.

After harvesting, the crop should be moved to a new enclosed area or section of the greenhouse for processing. This can be a packing house, cooler, or separate room from the main growing area. These areas can be as simple as a shed with protection from elements and running water, to more advanced and modernized facilities with mechanical lines, sorting stations, walk-in coolers, and more. No matter the scale and type of operation, the grower needs to be aware that all initial post harvest conditions need to be met to maintain quality. 

After moving to the desired location or area separate from the growing area or field, crops should be stored in their optimum temperature ranges and humidity levels. Additionally, some crops can not be stored with other crops as they will create an unideal environment creating adverse chemical reactions. Luckily there are procedures and equipment that can be used to reduce the degradation of post harvest storage.  

Post Harvest Shelf Life

Once harvested crops and related products are on a specific time crunch. At the moment of harvest, there are many biochemical processes that continuously change a plant’s original composition. These processes will continue to process until the product or crop is completely unmarketable. The period where the product is still sellable or marketable is known as the crop’s postharvest shelf life. This can be determined based on the crop and objective methods that determine the overall physical characteristics of the product. 

In addition a knowledge base of the science of plant processes at the end of harvest is ideal. For more information on the science of post harvesting see this article. With an understanding of the science, preparing and actually storing the crops will be much easier. In the control aspect of storage and handling, there needs to be temperature controls, gas control, humidity control, and grow lighting requirements. 

Cooling

The first thing that should be done is storing crops in the ideal temperature range. Failure to do this in a timely manner will result in the loss or degradation of the crop’s quality. In most cases this can happen quite quickly. All crops regardless of type are all vulnerable to some degree to pests and spoilage, however, the overall control of temperature, relative humidity, and other storage conditions can greatly increase the shelf life of the crop.

In storage, improper handling, as well as biological deterioration through various avenues leads to decay, loss of nutritional value, and changes the overall physical looks of the product. The main factors that influence the rate of deterioration and decay are air velocity, temperature, atmosphere conditions in concentrations of oxygen, CO2, and ethylene, and the temperature. Pathogens, disease, and pests all thrive in warm and humid conditions so the control of these greatly influences the shelf life of the stored crop. Overall most factors that can cause the loss of quality and product can be controlled and reduced through temperature control.

When looking at methods for cooling in a commercial greenhouse there are two factors that need to be considered. The first is the movement of heat within the product itself and then the absorption or loss of heat to the product surface. Both these processes are directly influenced by physical and chemical characteristics of the plant's material.

The temperature change in freshly harvested plant products typically involves the overall removal of heat when crops are harvested; they typically contain more heat at harvest than is normally acceptable for long-term storage and handling . This is especially true for highly perishable fruits, vegetables and flowers as well as grain and pulse crops if the moisture content is high. By cooling a crop after harvest, a grower can separate the process into two main stages- the removal of heat from the field and the maintenance of that temperature of the continued removal of respiratory heat and heat moving into the storage environment. The more perishable the product more quickly this needs done. 

One of the main components of cooling is through refrigeration. Refrigeration allows for the extraction of heat from a substance or product, thus lowering its temperature and keeping the temperature below that of its overall surroundings. Common cooling media that come into contact with the product or air, water, and ice. Each of these differ somewhat in the relative importance of various means of heat transfer.

There are two basic objectives in using refrigeration: the first is to get the medium cold so that it will act as a heat sink and to keep it cold as its medium begins to absorb heat and warm up. Through the use of mechanical refrigeration, a grower is able to allow for continuous removal of heat absorbed by the media and reduces the need for continuous changes in large media volumes.There are several different refrigeration techniques such as direct vaporization of a liquid, vapor compression, favor absorption, air cycle, vapor jet and thermoelectric cooling. No matter the method of cooling scientific evidence points to a direct link to temperature and potential shelf life of horticultural products. 

Data and research has shown that the higher the storage temperature, the shorter the shelf life of horticultural products. To a certain degree, the lower the temperature, the lower the deterioration. This is in part to the metabolism and other plant processes being slowed. Some crops can not be stored below a certain temperature, as colder temperatures can lead to tissue damage and overall quality reduction. Research should be conducted on specific crops to ensure proper cooling of crops. 

Atmosphere Control

In order to effectively store and handle crops after harvest, a controlled atmosphere should be used. A controlled atmosphere is a storage method in which concentrations of gases such as oxygen, carbon dioxide, and nitrogen, as well as the control of temperature and humidity of the storage room are regulated to precise measures. No matter the type of crop whether it is dry or fresh fruits and vegetables, the use of a controlled atmosphere is highly recommended. 

For dry crops such as grains and legumes its controlled atmosphere is used to primarily control insects and pests. it is known that insects can't survive without oxygen or conditions of a raised carbon dioxide of greater than 30%. These atmospheres to control insect pests and dry commodities can be created by adding pure carbon dioxide or nitrogen or have a low oxygen exhaust of hydrocarbon combustion, as well as using the natural effects of respiration from the crop itself to reduce oxygen and increase the carbon dioxide in the air. 

For fruit and vegetable crops the method that's most commonly used with controlled atmosphere is on apple and pear crops because the combination of altered atmospheric conditions introduce temperature that allow for prolonged storage with only a slow loss of quality over time.The overall goal of long-term storage of vegetables and fruit is inhibiting the ripening and aging processes. This in return retains flavor and quality.

Normal atmosphere consists of approximately 78% nitrogen, 21% oxygen, and 0.3% carbon dioxide and smaller amounts of other gases. However, in a controlled atmosphere the oxygen is reduced to 1.5 to 2% by replacing with nitrogen and a little bit carbon dioxide which is already produced by the fruits period under this controlled atmospheric conditions the quality and freshness of the crop are able to be retained in many products. These can be stored for on average two to four times longer than usual. 

Packing and Shipping

In order to adequately and correctly pack and ship crop material after a harvest, a grower should have knowledge of USDA grade standards and consistent application of the standards during the packing .This is critical for a quality pack.

Any area used for packing and shipping should be large enough to contain any equipment necessary for sorting, sizing, washing a certain crops, and permit the storage of excess inventory such as containers, labels, and anything else that may be needed; and adjoin with any cooling and storage facility. Depending on the size and scale the operation automation may be required to assist in the efficient process. The shipping container that the crop product is stored in is also a critical component in maintaining quality during handling and shipping. The shipping container used should be compatible with the intended crop and provide enough ventilation for rapid cooling and for the release of gas for certain crops.

Precaution should be taken on the container if it may come into contact with other elements such as water or ice. the container should also be clearly labeled for the crop, grade, count, and any other pertinent information that identifies the harvested material. The use of pallets also aids in the cooling and aeration of the crop and should have base dimensions that permit complete coverage of the pallet surface with 5 to 10 containers per layer depending on the size of the packaging and shipping containers.

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About MORR Inc.

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