Methods for Cooling Apples After Harvest

Apples are one of the most popular fruits in the world. Estimates place the amount of apples grown worldwide to have been about 69 million tons in 2010. Proper apple handling, cooling, and storage is essential to the overall quality and taste of the ultimate apple or apple product that makes its way to end consumers. Fortunately there are several excellent cooling and storing methods available to those who grow, ship, and sell apples.

General Facts About Apples

There are over 7,500 known varieties or cultivars of apples. Each different variety comes with its own set of characteristics; however, just about all are susceptible to some extent to bruising and mechanical damage. As such it is important for harvesters and workers to avoid dropping apples, or over-stuffing boxes.

Apples are susceptible to sun and heat damage. For this reason it is crucial that harvested apples not be allowed to sit in the sun for hours and that apple boxes and crates be well ventilated. Apples should also be cooled as soon as possible after harvesting to slow deterioration and quality loss.

General Information About Cooling and Storing Apples

For the successful cooling and storing of apples it is important to keep the following considerations in mind: respiration and its effect on degradation, relative humidity and its effect on the apple’s water and weight loss, chilling and re-chilling and how it can contribute to bacteria or fungi growth, and cooler and equipment maintenance and the impact this has on apple cooling and storage.

Respiration and Degradation – Apples continue to respire even after they are picked. It is this respiration which is largely responsible for their degradation and general loss of quality. However, respiration can be slowed if the apples are properly cooled, thereby minimizing degradation, maintaining quality, and extending shelf life.

As a general rule of thumb, the higher the holding temperature the greater the respiration and softening rate. Most varieties of apples will respire and degrade at twice the rate when they are kept at 40°F versus 32°F. At 60°F apples will respire and degrade a startling six times faster than at 32°F. It is generally a good idea to avoid subjecting the apples to temperatures more than a degree or two below 32°F, however, because they could suffer freeze damage.

Another important point to remember is that most coolers and thermometers will measure the temperature of the air rather than the temperature of the apples themselves. The actual apples are often a few degrees higher in temperature.

Relative Humidity – Relative humidity is an important factor in apple cooling and storage because if the relative humidity is too low it will cause the apples to dry out and suffer weight loss. Most varieties of apples need a relative humidity of about 90% to 95%. In some cases this will require the use of humidifiers in the storage rooms to add water vapor to the air.

Storage – Apples are known to “sweat” when they are removed from a cool storage environment and abruptly exposed to warm air. Likewise this sweating may occur if the cooler or storage facility is opened and warm air is allowed to enter. What is actually happening is that moisture is condensing on the apples. While this does not itself directly harm the apples, it can contribute to bacterial and fungal growth. Chilled apples should also not be allowed to warm up and then be re-chilled, since this can also contribute to the problem.

To prevent the growth of pathogens it is crucial that storage rooms and containers be kept clean and sanitary. Likewise, while apples prefer high relative humidity levels of 90%-95% the humidity should not be allowed to reach the saturation point of 100% since this too can cause moisture and condensation to form and once again promote bacterial growth.

Cooler Maintenance – Good cooler maintenance is also crucial to the proper cooling and storage of apples. The thermostats and humidistats should be periodically checked for accuracy, fans, ducts, and refrigerations coils should undergo routine cleaning and inspection, and gaskets should be checked to confirm a good seal. It is also important to monitor the cooler for potential air leaks or damaged insulation. Good upkeep and cooler maintenance will also help keep energy costs as low as possible and extend the service life of the cooler.

Methods of Cooling Apples

There are several different appropriate methods for cooling apples including: room cooling, forced-air cooling, and hydrocooling. Apples that are being stored long-term may also be subject to controlled atmosphere storage. What follows is a brief description of each as they relate to apples.

Room Cooling – Room cooling involves placing the apples in a chilled room such as a cooler to allow them to cool gradually as a result of ambient conditions. When it comes to room cooling it is important that the apples be well-ventilated, otherwise apples near the center of the boxes may not properly cool. The bulk apple boxes themselves should be stacked at least six inches apart from each other and at least eight inches away from an external wall or ceiling.

Room cooling is one of the least expensive methods of cooling apples and it also has the benefit of requiring little extra handling and labor since the apples are also likely to be stored, at least short-term, in the same refrigerated room that did the cooling. However, room cooling also has the disadvantage of being one of the slowest methods of cooling apples and it generally takes anywhere from several days to two or more weeks to fully cool the apples. Apples in the middle of the box may never fully cool since there is a natural heat increase from respiration and these internally located apples may be too far away from the cool air to fully benefit.

Forced-Air Cooling – Forced-air cooling involves forcing cool air past the apples to ensure contact and greatly increase the rate of cooling. Forced-air cooling is about four to ten times faster than room cooling. Because forced-air cooling relies so heavily on air flow, it is essential that the apple containers have plenty of open space and are well-ventilated. It is common for the apple crates to be arranged in a shell-type formation around the fan.

Using the correct fan for the job is crucial. Not all fans are able to generate enough pressure to fully move the air through the apples. A general rule of thumb is that the fan will need to be able to deliver around two to three cubic feet of air per minute per pound of apple being cooled. It is also worth noting that the fan will pull the air through the apples, rather than blowing it around them. This helps reduce damage and water loss. However, forced-air cooling nevertheless does run the risk of drying the apples out. That is why it is particularly important to monitor and maintain relative humidity levels when using forced-air cooling.

Hydrocooling – Hydrocooling is one of the fastest methods of cooling apples, faster than both room cooling and forced-air cooling. Hydrocooling involves submerging the apples in cold water to cool them. The larger the apple the longer it must be kept in the water. A general rule of thumb is that as the diameter of an apple doubles the amount of time it takes to cool the apple will also double.

Since the water is such a crucial element of hydrocooling it is very important that it be kept as cold as possible, generally as near to freezing as it can get while still being liquid. The water should also be very pure to avoid contaminating the apple and it must come into full contact with each of the apples. The water should also move past the apples quickly. Since hydrocooling requires a higher cooling load than other methods it is common to only cool the apples to about 45°F then finish the cooling using a different method.

Controlled Atmosphere Storage – Controlled atmosphere storage allows apples to be stored very long-term with only a slow, gradual loss in quality. As the term implies it involves keeping the surrounding conditions – the atmosphere – around the apple in a very controlled state. Temperature and humidity levels are closely regulated as are oxygen, carbon dioxide, and nitrogen levels since all of these gas concentrations can also affect the speed of degradation.

When selecting a cooling and storage method for apples it is important to consider factors such as the apple’s particular variety, the temperature at harvest, energy efficiency, how long the apples will need to be stored, and how much handling will be required. Naturally choosing a method which accomplishes your goals while keeping energy and labor costs to a minimum and apple quality to a maximum will be desirable. SEMCO/SEMCOLD LLC offers a full range of cooling devices ideal for apples which can be customized to fit each customer’s capacity needs.

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Methods for Cooling Blueberries After Harvest

Research has shown that blueberries tend to be an impulse buy for most consumers rather than a planned purchase. For this reason it is imperative that the blueberries which eventually make it to grocery stores be fresh, high quality, and visually appealing. In order to accomplish this goal the blueberries must be well cared for from planting, growth, and harvest, right on through to cooling, storage, transport, and display. The cooling and storage segment is especially important because it is during this crucial phase when the blueberries will either shrivel, rot, and decay or maintain their quality and thrive.

General Facts About Blueberries

Blueberries are commonly classified as either highbush or lowbush, with the term highbush referring to larger varieties of cultivated blueberries, including the vast majority of those commercially sold, and the term lowbush referring to smaller, wild varieties of blueberries, which are not as commonly sold. Blueberries are an early summer fruit and are highly perishable with a relatively short shelf life compared to many other types of fruits of vegetables. Depending on the weather and other conditions a blueberry field may be harvested as many as four times during the season, typically in intervals of about five to seven days. If the fields are harvested less often the result is typically over-ripe blueberries which are not as suitable for transport and sale, while harvesting more often is typically an inefficient use of labor and resources.

Blueberries are very susceptible to physical damage from careless or rough handling, picking, or mechanical harvesting. They should thus be handled very carefully and it is imperative that they be cooled rapidly and efficiently to preserve quality and extend shelf life. A successful cooling and storage system for blueberries is paramount.

General Information About Cooling and Storing Blueberries

If blueberries are allowed to remain at field harvest temperatures they are extremely perishable and will being to decline in quality very quickly. Visible signs of decay may be evident in warm, wet blueberries as soon as 12 hours or less after they have been harvested. For this reason they should never be held all day without proper cooling and storage. They should also not be picked while wet, such as immediately after or during a rainstorm, because wet blueberries are more susceptible to postharvest decay organisms such as the ones that cause gray mold and Alternaria rot. As a general rule of thumb blueberries should never go more than four hours without being cooled, but should be cooled sooner still if possible.

Respiration – Like other fruits blueberries are alive at the time of harvesting and continue to respire even after they have been picked. There is a natural rise in temperature due to this continued respiration. It has been estimated that blueberries generate about 22,000 Btu of heat per day per ton due to respiration. This is enough to raise their temperature by as much as 6°F. If that extra heat is not removed by cooling it will hasten the ripening and decay process.

Proper cooling will dramatically increase shelf life and slow the decay caused by respiration. That is because the respiration rate is directly impacted by the temperature of the blueberries. Blueberries respire at almost 20 times the rate at 80°F compared to 40°F. That means that they have almost 20 times the shelf life as well. The optimum temperature to slow respiration and increase shelf life is about 33°F to 34°F.

Humidity – Blueberries have a high water content and require a high relative humidity to remain moist and flavorful. If there is not adequate humidity in the air this can result in the blueberries becoming dried out and suffering water-related weight loss. The optimum relative humidity for blueberries is between about 90% and 95%.

Freezing – Blueberries will freeze at about 28°F. Freezing is a viable method of extending shelf life, but it must be done intentionally and quickly and the temperature should then be maintained below 0°F. Blueberries may suffer freeze damage if they are unintentionally subjected to temperatures below 28°F and then allowed to warm up again.

Correct Method of Cooling Blueberries

One of the most common cooling methods is called room cooling. In room cooling the product is placed in a refrigerated room and allowed to gradually cool to the ambient temperature. However, this method is not suitable for blueberries because the cooling rate is too slow to prevent continued degradation and quality loss. A large part of the problem is that the containers, wrappers, and plastic needed to hold the blueberries acts a kind of insulation, keeping the heat in. Room cooling not only results in inadequate cooling, but also non-uniform cooling, with some blueberries getting significantly cooler than others.

Forced-Air Cooling – The solution to this problem is forced-air cooling. In forced-air cooling, the blueberries are arranged around fans which then pull cooled air through the berries. This results in a much faster, and more uniform rate of cooling. Depending on the particular circumstances, forced-air cooling is about 16 to 20 times faster for cooling the blueberries than attempting to use still-air room cooling alone. This results in blueberries that have a much longer shelf life and which will reach the end consumer in much better condition.

For businesses that sell blueberries and blueberry products, be they farms, factories, or grocery stores, quality is of the essence. It is the quality of the product around which the business will build and maintain its reputation and keep customers coming back. SEMCO/SEMCOLD LLC can help with this crucial area by supplying industry-leading, efficient, customizable blueberry cooling equipment and systems. Our products and product lines are versatile and can be developed to suit each customer’s unique requirements.

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Produce That Benefits Most from Hydrocooling

Proper cooling is essential for almost any type of produce in order to ensure that quality is preserved as fruits and vegetables begin their journey to the end consumer. Here at SEMCO/SEMCOLD LLC, we offer many different kinds of cooling systems and different cooling methods are better suited to different types of produce. In this article let’s take a look at hydrocooling and the produce that benefits most from this method.

Hydrocooling-Produce

Why Produce Cooling Is So Important

Good produce cooling is important for a number of reasons. Field heat, or the ambient temperature that permeates a plant while it is growing, can have many detrimental effects that begin to affect the produce as soon as it is harvested. These include wilting due to water loss, rapid cellular respiration that leads to softening, and high levels of ethylene production, which can make the fruit overripe. In addition, warmer temperatures are more hospitable to decay-causing microorganisms such as molds and bacteria.

Proper cooling as soon as the crop is picked can slow, delay, or even prevent many of these undesirable processes. It is important to ensure that field heat is rapidly dissipated as soon as possible after the produce has been harvested. This keeps fruits and vegetables fresher for longer, decreasing the urgency to sell and improving overall quality once it is purchased.

Hydrocooling Basics

Hydrocooling is a cooling method in which produce is directly cooled by chilled, near-freezing water. This cold water runs over the fruits and vegetables, quickly dropping their temperature and eliminating problems due to heat. The water is cooled either with ice, a refrigeration system, or a system specially designed for hydrocooling.

The Advantages of Hydrocooling

There are many benefits to hydrocooling. One of the biggest is that it is very rapid; water transfers heat away from food up to 15 times more rapidly than air does. Hydrocooling systems can be designed for a range of operation sizes, capable of handling both small loads and very large ones. Also, hydrocooling helps prevent moisture loss in produce, ensuring that the fruits and vegetables will not dry out—a common concern with some other types of cooling systems.

In addition, depending on the design of the system, hydrocooling can also act as a way to partially wash the produce. This is not true, however, for hydrocooling systems where the water is recirculated without being purified. These are a few of the reasons why hydrocooling is a popular option among produce growers.









Important Considerations for Hydrocooling

A number of factors should be taken into account when trying to decide if hydrocooling is the best option for a crop. One of the biggest is concern about rot and disease. Although colder temperatures discourage decay, wet environments are friendly to microorganisms, meaning that some of the disease-prevention benefits of cooling can be reduced. For many types of produce, this difference is negligible, but foods that are especially susceptible to disease should not be hydrocooled.

In addition, the type of packaging should also be considered. Hydrocooling should be avoided for packages that are not water permeable, preventing the water from flowing inside and around the produce. Also, the packages must be designed to drain well, so that the water does not collect and pool in the storage area. Mesh bags, bulk bins, and wire crates are well-suited for hydrocooling; palletized produce can be hydrocooled if it is stacked correctly.

Finally, it is important to note that hydrocooling is primarily a pre-cooling method meant to remove field heat rapidly. Hydrocooling is not advisable as a standalone cooling method because at lower temperature it is not energy efficient. Hydrocooling is often done in conjunction with room cooling or forced-air cooling.

Best Produce for Hydrocooling

There are many types of fruits and vegetables that respond particularly well to hydrocooling. These include:

  • Apricots
  • Peaches
  • Plums
  • Nectarines
  • Cantaloupe
  • Apples
  • Pears
  • Cherries
  • Spinach
  • Lettuce
  • Endive and other greens
  • Leeks and Green Onions
  • Asparagus
  • Broccoli
  • Snap Beans
  • Pea Pods
  • Brussel Sprouts
  • Cauliflower
  • Turnips
  • Cucumbers
  • Corn

Foods that should not be hydrocooled include those that are highly susceptible to wetting, such as berries, potatoes, bulb onions, and garlic. This type of cooling should also be avoided for citrus fruits, mushrooms, grapes, and squash. For information regarding cooling methods for particular types of produce be sure to check out our past articles.

SEMCO/SEMCOLD LLC Designs Great Hydrocooling Systems

Here at SEMCO/SEMCOLD LLC, we are proud to offer a wide variety of cooling solutions to our clients with our specialty design, manufacture, and installation services. Hydrocooling is just one excellent option for keeping your produce fresh and your quality high. Contact us for more information regarding the system that is best for your crop.

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