Field heat should be removed from fresh fruits, vegetables, and flowers as quickly as possible after harvest. Each commodity should be maintained at its lowest safe temperature. Cooling and storage requirements for specific commodities are presented below, in NC Cooperative Extension Service Publication AG-414-1, and USDA Agricultural Handbook No. 66.
Proper postharvest cooling can:
- Suppress enzymatic degradation (softening) and respiratory activity
- Slow or inhibit water loss (wilting)
- Slow or inhibit the growth of decayproducing microorganisms (molds and bacteria)
- Reduce the production of ethylene (a ripening agent) or minimize the commodity’s reaction to ethylene
In addition to protecting quality, postharvest cooling enhances marketing flexibility by
making it possible to market fruits, vegetables, and flowers at more optimum times. The ability to cool and store commodities minimizes the need to market immediately after harvest. This can be an advantage for high-volume growers as well as pick-your-own (P-Y-O) operators and those who wish to supply restaurants and grocery stores.
Field heat removal method choices depend on several factors, including:
Temperature of commodity –
Nature of the commodity(ies) – type of product (e.g., leafy greens, flowers, fruit) respiration rate(s), cooling requirements, lowest safe temperature, tolerance of exposure to water
Product packaging requirements – box, bin, or bag; because packaging materials and design configurations affect method and rate of cooling
Product flow capacity – volume of commodities which must be handled per unit of time will determine the appropriateness of cooling methods and systems
Mix of commodities – compatibility depends on their nature with regard to sensitivity to odors and volatiles, such as ethylene.
Economic constraints –
construction and operating costs vary among methods; expense must be justified by volume and/or price increases related to cooled products.
Market requirements or expectations – e.g., top-icing broccoli.
Common Produce Cooling Methods Room Cooling – Placing commodities in an insulated room equipped with refrigeration units to chill the air. This method can be used with most commodities, but is slow compared methods discussed below. Used refrigerated truck bodies make excellent small storage rooms.
Forced-air cooling – Used in conjunction with a cooling room is effective for most packaged commodities, and is 75 to 90% faster than room cooling. Fans should be
equipped with a thermostat that automatically shuts them off as soon as the desired product temperature is reached.
Do not operate forced-air fans after the commodity has been cooled to its optimum temperature. A lowcost, portable, forced-air pallet cooling system has been developed for small quantities of a commodity (see reference).
Hydrocooling – Can be used on most commodities that are not sensitive to wetting. Water removes heat about 5 times faster than air, but is less energy efficient. Mechanical
refrigeration is the most efficient method of cooling water. A thermal storage immersion hydrocooler system can be economically fabricated for various volume needs. Ice in
water will also provide a source of coolant. Used, stainless steel bulk farm milk coolers may be excellent options for some growers. If hydrocooling water is recirculated, it should be chlorinated to minimize disease problems.
Top or liquid icing – May be used on a variety of commodities and is particularly effective on dense and palletized packages that are difficult to cool with forced
air. Because of its residual effect ice methods work well with high respiration commodities such as sweet corn and broccoli. One pound of ice will cool about three pounds of a commodity from 850 to 400F.
Refrigerated trucks are not designed to cool fresh commodities. They can only maintain the temperature of loaded products, so cool commodities before loading.
Alternate Cooling Sources
Field heat removal is a function of exposing products to an environment which has a temperature lower than that of the commodity. When the above-mentioned cooling
methods are neither practical nor expedient to employ, alternatives that will often suffice, especially for smaller volumes of commodities, include the following:
- Well water – Temperatures are usually in the 500 to 600F range
- Night-time – Air temperatures are usually cooler from sundown to sun-up, good time to harvest some commodities
- Streams – Water temperatures are usually cooler than air, especially if flowing from mountains. Test to be certain that this water is free of contaminants
- Altitude – If easily accessible, higher elevations can provide cooling
- Cellars/Caves – Generally maintain fairly constant, cooler-than-air temperatures
- Discarded truck bodies, etc. – Can be buried in hillsides for storage of some commodities
- Shade – If refrigeration is not available, at least keep commodities from warming up
- Time of harvest – Mornings are preferred, when commodities are usually coolest
At Unitec we believe that knowing more aboutthe process will assist you in making the right decision about your system.
A trained and knowledgable consultatn will meet with you to discuss your exact needs. We know the area and have done work in the past and it is this experience that we will draw on when advising you on the best system to go with. This means a full assessment of the fields, the current requirements as well as what is needed into the future.
Research & Development
We then take all the information retrieved from the meeting/s and go to work creating a tailor-made solution for you. This entails researching the latest equipment, which we obtain from the EU and UK as we only use "best of breed" as a standard policy. The materials we select are all HACCP, BRC and Eurogap compliant, meaning you are getting a future with your equipment.
For your interest and reference, download the HACCP document.
Once back at the office, we go to work putting together the ideal system to meet your needs. Taking into consideration the area, your land configuration, and the position of roads, etc. In this stage, we create a comprehensive list of all the items and equipment needed, and who is responsible for doing what on the project - meaning client and Unitec.
Also factored into this are the various stages of municiple and building inspections and requirements, and other testing.
we do a "test run" on the equipment and , based on the information retrieved from you and from what we know of the area. Climate, rain falls, maxium and minmum temperatures, all get factored into the equation as does the budget you are working to.
This is then presented to you as a total solution. Each stage is justified and explained to you, so we impart an understanding of what we are proposing and why, which we believe will assist you in drawing the right conclusion regarding your postharvet cooling solution.
our aim is simple, to deliver tailored post-harvest cooling solutions through a conceptual understanding of the cooling requirements, deliver the best solution built with the best equipment and technology available - standardly and to offer convenient after-sales services and maintenance of our supplied equipment to enable maximum up-time to all our clients, in and around the South African markets.
The equipment comes in the form of self-contained units which can be floor or ceiling mounted. The water contact coolers produce air at 1 deg C at near saturation point. Those fitted for Univeg employ a total of 260 kW, but for smaller units, suitable for on-farm use, start at 2.2 kW.
Unitec managing director, Ian White, reckons to provide all equipment, store design and installation, from the concrete pad upwards, using his own in-house engineers and technicians.
"What we are doing is gaining time by extending the life cycle of the produce enough to ensure that it gets to the consumer in afresh and attractive condition."
"It's a common misunderstanding among vegetable storage experts that very high humidity levels accelerate mould growth and tissue decay. Produce stored in a room at 90 per cent relative humidity will lose moisture six times faster than if stored in a room at 100 percent RH.
This takes place once the installation date is agreed to and all the pre-installation stages are complete. Our installation crew arrives and sets up all the prerequisites then carries out the installation in the most expedient manner.
Installations differ from one project to the next.
Maintenance & Support
At Unitec our aim is simple, to deliver you the best produce handling equipment available.
Once installation has been completed, testing and inspections are carried out before the plant is fully commissioned and handed over.
We also provide these key services
Pack Shed Lighting
We will design and give you a detailed lighting diagram that will maximize the use of the available power as well as assist you in placign redundant lights thus absorbign reqources and adding expense to you running costs.
Dual Discharge Blower Coils
To be recognised globally as the leading provider of innovative, quality produce handling equipment and be renowned for our commitment to excellent customer service.