Reducing post-harvest losses of fruit

By Ilana Koegelenberg

Every link in the cold chain has a role to play in reducing food waste. Starting at the source, what role can refrigeration play to minimise food wastage on farms? 

Food waste is one of the most significant problems facing the global food supply. In fact, according to the United Nations, a third of all the food produced in the world for human consumption is wasted.

HAR003When exporting citrus for a steri market, there are very strict regulations in terms of temperature control. (Taken at the Fresh Produce Terminal in Cape Town.)
Image credit: Ilana Koegelenberg

From farm to fork and beyond our borders and oceans, we throw away more food than people even realise. But we don’t have to. Some food wastage will always be unavoidable. But by strengthening the cold chain, produce will have an improved shelf life, increasing its chances of consumption as opposed to simply being thrown away, rotten, useless.

To learn more about refrigeration’s role in reducing post-harvest losses on fruit farms, we chat to three prominent industry associations about their experience and insights, looking at table grapes, citrus, and subtropical fruit in particular.

Reducing food waste is a global problem. But we can make a difference locally. Through clever engineering and out-of-the-box thinking, we can do our part in alleviating world hunger.

HAR001When exporting fruit, refrigerated containers need to be used to ensure that the cold chain isn’t broken and that the fruit last longer.
Image credit: Enterprise IoT Insights

How big is the problem really?

So how much is actually wasted? It is hard to say in South Africa specifically …

“One often hears broad statements that 30–40% of all fresh produce goes to waste. When someone claims these figures for export produce to discerning markets, one tends to question the claim, since the table grape export industry will not survive at such high levels of waste,” explains Dawie Moelich, manager: technical and market access at the South African Table Grape Industry (SATI).

Exported table grapes are seldom wasted ‘in totality’ and when this happens, it can usually be traced to a specific failure of equipment. Sometimes, mild deviations from quality specifications or non-conformity on arrival, can have financial implications due to a requirement for re-packing or diversion to less-discerning buyers and lower price structures, explains Moelich.

Accurate figures on the extent of non-conformity leading to financial losses are not easily available. When large claims are received, it is essential to objectively establish the possible cause. If an incorrect assessment of the possible cause or causes is made, non-appropriate ‘corrective measures’ may be chosen, leading to even more unintentional consequences. “Make sure that quality claims based on quality control (QC) reports conducted on a limited quantity of grapes are well substantiated, before making adjustments to well-proven practices on a large scale,” Moelich advises.

For citrus, it is also hard to get an exact figure. “This is difficult to say, but I would estimate that 3–6% of exported citrus cannot be sold in the market,” says Dr Tarl Berry, Citrus Research International, Department Horticultural Science, University of Stellenbosch. Dr Berry and his colleague Dr Paul Cronje answered the questions on behalf of the Citrus Growers Association of Southern Africa.

“It is difficult to measure how much produce is actually wasted in terms of post-production losses,” says Kamukota Kaluwa, South African Avocado Growers Association (SAAGA) horticulturist / technical advisor, on behalf of the larger Subtrop Association, which also includes the South African Mango Growers Association (SAMGA) and the South African Litchi Growers Association (SALGA). “This information varies with each individual pack house,” he says. “Accurate figures can be obtained from the individual pack houses.”

It may be hard to pinpoint an exact figure, but it is undeniable that food waste does occur. How can it be addressed with the help of refrigeration?

HAR004The motivation to apply proper cooling in citrus is driven towards preventing microbial decay and disorders, and meeting phytosanitary requirements.
Image credit: Pixabay

Cooling is key

Cooling from very early on is vital when it comes to most fruits.

For table grapes for example, forced-air cooling should ideally start as soon as possible after the table grapes are harvested (cut from vine), explains Moelich.

In practice, the refrigeration is delayed for a while, to facilitate the preparation, packing, and palletisation of table grapes. Operationally, there is often a build-up of harvested grape bunches produce prior to the sorting and packing line, in which case evaporative cooling is employed to reduce field-heat and raise the humidity surrounding the fruit. “There is no doubt, though, that the sooner forced-air cooling refrigeration can be initiated, the better,” explains Moelich.

“Storage life of fresh fruit is directly affected by the lapse of time and the level of temperature maintained during the multiple components of the export chain.”

When it comes to subtropical fruit, refrigeration comes in immediately after harvest as well, explains Kaluwa. It is also used when storing fruit in the pack house and during transportation to the market. A valuable step in the subtropical cold chain from the start.

In citrus, cooling starts a bit later. The first step of the cold chain occurs in a cold store near to the port, explains Dr Berry. Here the fruit is either pre-cooled using forced-air pre-coolers, or are loaded at ambient temperatures into the containers. The container then reduces the product temperature to set-point to start the cooling process.

Shelf life

Refrigeration has a massive impact on the shelf life of produce. “Storage life of fresh fruit is directly affected by the lapse of time and the level of temperature maintained during the multiple components of the export chain,” says Moelich.

The grape berries, stems, and bunches are living organisms and after removal from the vine (harvest), metabolic processes continue at cellular level, which eventually leads to senescence. “Low temperature remains the single-most effective technology at our disposal to slow down various processes which are associated with the loss of quality of fresh produce, including the rate of moisture loss,” he explains.

In the post-harvest environment, the respiration rate of produce is most commonly used as a parameter to explain and demonstrate the rate of biological activity. The respiration rate as well as the rate of moisture loss of the grape stems and the grape berries are very different and present different challenges in terms of maintenance of post-harvest quality, within the same pack. Without refrigeration — in combination with the barrier properties of specific packaging components — there would be almost no chance of marketing table grapes in the distant markets abroad, says Moelich. “It simply makes a lot of sense to optimise the refrigeration process.”

It is important for citrus, too. Proper pre-cooling is vital to reduce decay and physiological disorder development in citrus, confirms Dr Berry. However, more importantly, it is used to cool fruit to comply with phytosanitary temperature protocols to markets like the US, China, and EU.

It should be noted that citrus fruit are non-climacteric and are therefore harvested after they have ripened on the tree, explains Dr Berry. Citrus also have a relatively low respiration rate compared to many other fruit types. “The motivation to apply proper cooling is therefore less motivated by a need to regulate respiration rates (still important) and instead more driven towards preventing microbial decay, disorders, and meeting phytosanitary requirements.”

For subtropical fruit, refrigeration is simply non-negotiable. “Proper refrigeration slows down the metabolism of fruit, therefore slowing down the ripening process and increasing the shelf life of the produce,” explains Kaluwa.

HAR006For subtropical fruit, the most common mistake producers make is that they begin refrigeration too late, when the ripening process has already begun.
Image credit: Pixabay

The stakes are high

There are great risks involved in not keeping fresh produce at the right temperature — whether that be too hot or too cold. Getting the temperature exactly right is vital.

When it comes to table grapes for example, the optimum temperature for transportation and storage is between -0.5°C and +0.5°C, Moelich confirms. Outside of this range, you run the following risks:

Freezing damage: To successfully maintain pulp temperature at the optimum level, the delivery air must be lower than the pulp target temperature, typically between -0.5°C and -1.5°C. Therefore, there is a narrow temperature range that must be maintained to avoid freezing injury, which is reported to occur at -2.7°C in ripe table grape berries and -2°C in the stems. Although it becomes particularly challenging to avoid freezing temperature during the preparation of specific ‘cold treatment’ consignments (where the target pulp temperature is a maximum of -0.55°C), a recent survey of the currently approved facilities indicated that the cold store operators are indeed able to avoid freezing temperatures, within a safety margin, during the pre-loading phase. Still, each individual consignment requires diligent monitoring.

Post-harvest decay: There are several potential post-harvest pathogens, such as Botrytis, Penicillium, and Rhizopus, which are able to develop and spread faster on table grapes at storage temperatures above 0°C, even with the inclusion of SO2 sheets. Therefore, maintaining the storage temperature at -0.5°C will reduce the risk for these pathogens spreading during transport and storage. Conversely, transportation and storage between 2°C and 5°C or above, will increase the risk of decay development.

Condensation: It is unavoidable that short and minor temperature breaks will occur during the handling of grape pallets within the export chain. The combination of the various packaging components acts as a mild form of insulation and specific components are designed to buffer and absorb a limited amount of condensation. However, severe temperature breaks at any stage of the export chain, including the on-farm pack house, will result in excessive condensation, which aggravates berry splits and SO2 bleaching.

Phytosanitary risk management: The management of phytosanitary risk and therefore the requirement to avoid the importation of live phytosanitary pests into pest-free markets, are agreed by means of bilateral technical protocols. Low-temperature management techniques are frequently prescribed to manage the risk of specific ‘pests of concern’. In-transit exceedance of the maximum allowed pulp temperature during a specified period will lead to rejection on arrival, which means the consignment needs to be returned without opening of the container, or diverted. Fortunately, table grapes can withstand low-temperature storage without the risk of the development of ‘chilling injury’. The routine shipment of pre-cooled grape consignments at a set-point of -0.5°C is therefore inherently suitable as an important measure to the table grape export markets, to manage the risk of phytosanitary pests.

The maintenance of post-harvest quality starts when the table grapes bunches are harvested.

Image credit: Pixabay

When it comes to citrus, the risks are very similar. When the temperature is too high, the fruit will lose quality and decay will develop, Dr Berry explains. Additionally, at too low temperatures, chilling injury and even freeze damage will negatively affect the fruit market value. Chilling/freezing damage is particularly challenging in the case of phytosanitary/steri markets (for example the US and China). These markets have very strict temperature protocols, for example temperatures should not exceed -0.6°C. Whereas, generally, 4.5°C would actually be a much more preferable storage/shipping temperature.

Simply put, if temperatures are not cool enough, then the fruit will ripen normally, leaving it susceptible to post-harvest diseases. If temperatures are too low, the fruit will experience ‘chilling injury’, explains Kaluwa.

Cooling options

Now that we have established that cooling is not optional, we take a look at what refrigeration systems are commonly used to cool products.

For table grapes, evaporative cooling is used on harvested grapes prior to packing, while forced-air cooling is used during initial cooling of pallets. Refrigerated transport is needed for long-distance movement between cooling facilities, and in terms of export, refrigerated containers are used for shipment to markets.

Forced-air cooling is also used in citrus export. In this case, cold airflow is extracted (using fans) through the pallet stacks to remove excess heat from the fruit more rapidly, explains Dr Berry. “This approach is useful, as the packaging creates a thermal barrier around the fruit, which greatly reduces fruit cooling rates compared to if the fruit were still in bins.” This takes about one or two days, but three days is usually used (regulated).

Static cooling is also an option on citrus, but this takes much longer than forced-air cooling. Packaged or unpackaged (in bins) fruit can also be placed directly in a cold store.

Ambient loading is also popular for citrus. Packaged fruit are loaded warm (or only partially cooled) into a refrigerated container. The refrigerated container then gradually reduces the fruit temperatures over three or four days. “This approach is highly valued, as it allows fruit to bypass pre-cooling facilities, particularly important during peak seasons,” explains Dr Berry.

Regarding subtropical fruit, your options are: room cooling, forced-air cooling, and hydro-cooling, with refrigerated containers when transporting produce abroad.

Cooling of table grapes should start as soon as the grapes are harvested and reach the pack
house. (Taken at a new pack house in Wellington.)

Image credit: Ilana Koegelenberg

A word of advice

Here are some tips from the experts on how to get the most out of fresh produce and refrigeration systems.

Moelich warns against incomplete table grape pallets. At farm level, ‘excess’ or incomplete pallets, which cannot be placed under forced-air cooling conditions immediately or soon after packing and are then kept under static refrigerated conditions until the next packing shift, are particularly prone to excess condensation. “Avoid this practice as far as possible,” he says.

“Know your refrigeration system well,” Moelich advises. “Install proper monitoring equipment.” Rather measure too much than too little, on both the centre and sides of the stacked grape pallets, using a combination of thermocouples and probes. Make sure the thermocouple wires are correctly placed in the centre of the pallet. If not, you will not know your pallet’s actual temperature status, and this will create problems later in the export chain.

All cold stores should be profiled to know the location of both the warmer and colder spots, Moelich advises. Such profiling is also essential for the optimum placement of temperature sensors. The control system of the refrigeration unit relies on accurate inputs/feedback from the system. If these sensors are not optimally positioned, the accuracy of the refrigeration system can be compromised. For conventional cold tunnels, deflector panels or sheets can be installed to allow for an even delivery of cold air from the coil, into the room. This will avoid the risk of short-circuiting of cold air coming directly off the cooling coils through specific pallets, and it will reduce the possibility of freezing damage.

When you use external service providers for cooling of your export produce, make sure that you discuss and contract your expectations well in advance with the service provider.

Dr Berry agrees on the importance of temperature monitoring. “For citrus, time-temperature interaction is very important and should be carefully managed to ensure fruit are not exposed to overly low temperatures for too long,” he says. “This could cause significant quality problems.” To manage temperatures, technicians need to strategically position temperature probes in the respective forced-air cooling tunnel, cold room, or refrigerated container. In the case of forced-air cooling, temperature probes allow for the correct application of step-down cooling.

Step-down cooling is a good idea, Dr Berry advises. With this practice, temperatures are gradually decreased until they reach the desired set-point. This contrasts with just simply applying a single set-point temperature, which results in rapid cooling (potential for chilling injury).

“It is important to maintain the cold chain throughout the entire process of transportation and shipping,” advises Kaluwa. “Try not to break this cold chain!”

HAR007When commissioning a new cold store, make sure that your service provider is reputable and has sufficient knowledge and experience to design a unit that meets your expectations. (Taken at GoChill in Durban.)
Image credit: Ilana Koegelenberg

Common mistakes

The industry associations have been around the block and have seen many dos and don’ts over the years. They share some common mistakes that producers make and how to avoid them.

The maintenance of post-harvest quality starts when the table grapes bunches are harvested, and a sense of urgency and temperature awareness should be maintained even during those stages before the produce is placed under refrigeration, explains Moelich. In general, producers tend to have a reasonably good picture of the best-case scenarios within their typical handling chains, but not necessarily the worst-case scenarios. “Make an effort to know both scenarios, to identify where operational improvement is required.”

When you use external service providers for cooling of your export produce, make sure that you discuss and contract your expectations well in advance with the service provider, Moelich advises. Do not rely only on the single temperature recorder that is installed in the container during loading. Invest in the verification of your refrigeration process at your service provider, by using extra temperature recorders in random pallets, from farm gate.

“When commissioning a new cold store, make sure that your service provider is reputable and has sufficient knowledge and experience to design a unit which meets your expectations,” says Moelich. One sometimes hears about producers who are building a new cold store with cold tunnels that will cool table grapes within ‘x’ hours, but when the first grapes pallets are forced-air cooled, it takes ‘x plus 10’ (for example) hours to reach target temperature. When this happens, throughput and logistical efficiency are severely compromised.


Food wastage is a huge problem when it comes to fresh produce, and an alarming amount of fruit is thrown away before it can be consumed.
Image credit: City Fruit

For subtropical fruit, the most common mistake producers make is that they begin refrigeration too late, when the ripening process has already begun, explains Kaluwa. Another issue is time, when the cold chain is broken during loading and offloading of the fruit for transport. “This can be prevented by ensuring that fruits are loaded quickly.”

Ultimately, it all comes down to maintaining the cold chain and ensuring as little disruptions as possible. Reducing food waste isn’t just beneficial to the world and the environment; it’s beneficial to your pocket, too.

Are you part of the problem or part of the solution?

Check your cold chain!

FoodForward SA: addressing the problem

FoodForward SA was launched in 2009, with the aim of addressing widespread hunger in South Africa by connecting a world of excess to a world of need — by recovering surplus food from the consumer goods supply chain and using it to help feed people.

The way it works is that FoodForward SA partners with various stakeholders in the food supply, to help rescue food that would otherwise go to waste — and using that food as a catalyst for social change.

That includes partnering with commercial farmers across South Africa and urging their network of farmers to donate their extra food left over after harvest.

The organisation has dedicated refrigerated vehicles that go directly to the farmers to collect fresh fruit and vegetables while they are harvesting.

According to the organisation, food banking is the “most effective solution to reduce hunger, and reducing food waste is the third most effective solution for fighting climate change.”

And it’s working. Over 30 000 children across the country now benefit every day from the organisation’s school breakfast programme, it said. Meanwhile, 250 000 people are fed every day — and 17.6 million meals are provided every year.

A significant problem that the organisation has identified, is food waste within the agricultural sector.

Some 50% of all agricultural production go to waste, according to FoodForward SA — due to specific product requirements and processing inadequacies, or farmers not having access to markets.

FoodForward SA said it helps resolve this issue through its Second Harvest project, which works to encourage farmers, growers, food processors, and other supply chain stakeholders to partner with them and join the food recovery revolution.

For every tonne of food that they recover, four tonnes of greenhouse gas emissions are saved.

Click here to read the January/February 2018 issue of Cold Link Africa



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