Vertical Airflow Pre-Coolers™ Reduce Pre-Cooling Time and Save Energy Costs

Vertical Airflow Pre-Coolers™ can help savvy produce operators, to save pre-cooling time, which increases shelf life and quality for fruit and vegetables.

Global Cooling Inc., one of the leading innovators worldwide in forced air-cooling systems, designed and built the first prototypes several years ago.  Now, after three seasons of use and fine-tuning, Global feels confident about launching the product line worldwide.
“We think this is the future of the industry,” explained Global’s founder, Jim Still.  “Vertical airflow pre-coolers cost a little more than tarp tunnels, but the advantages are overwhelming.”

The vertical airflow pre-coolers’ main advantage is that they do not suffer from the pressure drops typical of tarp tunnels.  “This means that the cooling temperatures are much more uniform,” Still continued, “and the seven-eighths cooling time is reduced.”
This is because every pallet or bin is located at the same distance from the pressure fans and cooling coils.  “And not with some being right next to the source, and others being 20 feet away from it.”

The vertical airflow pre-coolers also require a smaller footprint, or floor space, than do tarp tunnels, saving valuable warehouse or cold room real estate.

Finally, each vertical airflow pre-cooler is provided in its own insulated panel enclosure, to prevent new loads from reheating loads ready to finish, and can have doorways at both ends, providing for first-in, first-out, product handling.  “It’s also safer and faster, from a material handling and flow viewpoint, to have loading at one end, and unloading at the other,” concluded Still.

“Pre-cooling” – which is the term for quickly reducing the temperature of fresh harvested fruit and vegetables, to ideal temperatures – greatly helps to extend the shelf life and net weight to sell, of almost all fresh produce.

Global Cooling is a leading supplier of refrigeration designs to fresh fruit companies in the Philadelphia region, and exports worldwide.

Precooling information can be found at:
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Did You Know Fresh Grapes Last for 2 Months or Longer with Proper PreCooling?

Grapes are the oldest fruit known to man. The Spanish are credited  with the introduction of grapes to America over 300 years ago.

Grapes are grown in the temperate zones around the world including  Africa, Asia, Australia, Europe, North America and South America.

California is the United States’ major grape producer.

The majority of Northern Hemisphere harvesting occurs in late August to early October. The majority of Southern Hemisphere harvesting occurs between the months of February and April.

When grapes are harvested, the fruit temperature can be anywhere from 71°F to 98°F.  Proper storage temperature is 0°F to 1°F.

The faster grapes are cooled from harvest temperatures to the proper temperature, the longer their shelf life, and the less their water loss (water loss also causes stem rot.)

Special rooms known as forced-air pre-coolers are used for rapid cooling of grapes.  Most of these quick cooling tunnels are able to cool 10 or 12 pallets of grapes from 95°F to 36°F in 6 hours or less.  Each pallet weighs about 2,00o pounds, so that is 20,000 or 24,000 pounds of grapes at a time.

Ironically, forced-air pre-cooling can also itself cause moisture loss, so “Ultra High Humidity PreCoolers” are often used.

Another important factor in extending grape shelf life, is cooling delays from time of cutting to entering the precooler.

Harvest crews might not be able to accumulate a 10 or 12 pallet lot of fruit, for 3 hours or more, so the first-cut fruit is older – by hours – than the last cut fruit.  When a full load of grapes has been collected, there is the factor of transportation time to the packhouse, where the precoolers are located.  There could also be a queue of fruit ahead, causing a waiting time to enter the precooler.

Early morning harvested grapes are cooler than afternoon harvested grapes, and this fruit is the ideal candidate for extended shelf life, preserving taste and eating quality for up to 2 months.

When grapes are stored in your home refrigerator, they will not last as long as in commercial cold storage, because your fridge runs at about 40°F, far above the ideal holding temperatures for the fruit.

Also, grapes can be harmed by airborne ethylene, mold, and mildew.  Many commercial cold storages now have ethylene scrubbers, which purify the air, and further contribute to extended shelf life and eating quality.

Humidifiers are also used to maintain relative humidity above 90%, which also helps.  Ultrasonic humidifiers are by far the most popular type, because of the extremely fine water droplet size they produce – 1 micron – which prevents water spotting or damage to the cardboard boxes.

Thanks for asking!  For more info, feel free to post a comment here, or eMail me at Or check out our website:

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Controlled Atmosphere Ripening – Part 3 – All about Ethylene Gassing

All about Ethylene…

How much ethylene gas is enough?  Can you use too much ethylene?  For how long do you gas?  Can you / should you use fresh air ventilation while gassing?

If you ask five different people, you might get 10 different answers <g>.

We have a number of installations, where the ripening rooms are equipped with ethylene sensor gassing control.  These rooms also have carbon dioxide sensors, to control fresh air ventilation automatically to a chosen setpoint.

Through working in partnership with our ripeners, we have been able to learn some interesting things about ethylene gas control.

First, when a room starts to gas, if the gas is working, the carbon dioxide (CO2) level in the room will rise.  This is a natural result of the increased respiration of the fruit, as it begins to ripen.  Higher CO2 levels, create a “modified atmosphere”, displacing oxygen, and can slow the ripening process.

So, we recommend using fresh air ventilation during gassing, to maintain consistent levels of oxygen and CO2 at all times.

Does this use more ethylene gas?  Yes.  But if we use the ethylene sensor to control the ethylene gas level, to 50 ppm, or some other low level, we actually use less gas than uncontrolled ethylene generators can use.

Second, for how long do we need to gas the fruit?  The primary contributing factor, for how long we need to gas, to ensure that all fruit in the room is initiated into ripening, is the temperature of the fruit.  At higher temperatures, the gassing duration can be shorter, not more than 24 hours.  At lower temperatures, we might need to gas for 36 or 48 hours.

Pressurized ripening rooms help to ensure that all fruit in a room gets uniform temperature, airflow, and exposure to ethylene gas.

Third, if you want to slow down ripening, set a colder fruit temperature, and turn up your CO2 control to a higher level, such as 2% or 3%.

If you have any more questions, feel free to posts your questions or comments here, or contact me:

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Thanks for reading!

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The Best Pre-Coolers are Here

The future of pre-cooling is here.

Vertical Airflow, Reversing Airflow, Ultra High Humidity, we have them all.

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Controlled Atmosphere Ripening – Part 2

The least understood component of fruit ripening, is carbon dioxide. (CO2)

We have seen CO2 at as high as 10%, in ripening rooms set to 67-degrees-F.  We are amazed that there has never been a reported incident of ripener CO2 asphyxiation, maybe it has happened, and no one knows why…maybe not.

When CO2 is at 10%, oxygen is at 11%…you cannot light a match in that ripening room, there is not enough oxygen to support the flame.

The question for ripeners is:  do high CO2 levels affect the ripening process?  The answer is: Yes, they do.

Respiration, or ripening, can be shown in a word equation:  glucose + oxygen -» carbon dioxide + water. (C6H12O6 +6O2 → 6CO2 +6H2O).

Photosynthesis (6CO2 +6H2O → C6H12O6 + 6O2)

So, at what level of CO2 does it start to affect the ripening process?  Many say that 1% is the level at which to control.

Another question: is ripening faster better?

If you want to hold back bananas, either green or yellow, set your temperatures for 56F fruit, and y0ur CO2 control t0 3%.  (If CO2 gets much higher, off-tastes can be developed, and a grayish “false chill” can occur.)

The fruit will not make any more CO2, so you have stopped the ripening process.

We are here to help you ripen better, and make more money doing it, with a much more foolproof process.

We also have the best precoolers in the world.  Ask us about them!

Ask us questions:

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Forced Air Pre-Cooling Basics

Forced Air Pre-cooling is being used more and more, especially with concerns about phyto-sanitary conditions of water-based pre-cooling methods (hydro-cooling and vacuum-cooling.)

Where do we start with design of forced-air pre-cooling?

How much air do we need? At what static pressure? How wide should the center tunnel be?  Do we need a center tunnel?  Do we automatically turn off the fans and cooling when we achieve desired temperature? Should we reverse airflow at 3/4 cooling?  Are tar;p systems the best?  Or the MACS automatic system?  ($100,000 versus $900,000!)

And how do we measure those variables, and where, and how often, and how does that impact the control system? Just for starters…

Let’s take this one step at a time….

Airflow – otherwise known as CFM (cubic feet per minute, or volume).  This can be extremely variable from design to design, but as a rule of thumb, we use 2,000 CFM per pallet.  This results in airflow per pound, of 1 CFM for heavy commodities such as bananas and grapes, and 2.5 CFM per pound for more delicate items. such as berries.  We can provide fans delivering 3,000 CFM per pallet, which is 1.5 CFM per pound for heavy items, and almost 4 CFM per pound for berries and leafy vegetables.

Static Pressure – this is the “Holy Grail” of pre-cooling, what will be the static pressure (SP), in inches of water column (or pascals or millimeters) ?  Our pre-cooling systems all have a minimum SP of 1.1″ SP. and options are available up to 3″ SP.

SP influences fan motor HP, the higher the SP, the greater the HP fan motors required.  Larger diameter fans normally require less BHP input, saving on  electrical costs to  operate.

Benefits of reversing airflow design.  Joint research conducted with a leading AG.Edu, concluded that pre-cooling time could be reduced by 20% by reversing airflow at 3/4 cooling time, thus cooling the warmest fruit on each pallet faster, than one-way airflow could.

Vertical airfow pre-coolers are the best way t0 do this.  They can also be installed outdoors, feeding into a cold storage room, with loading from one end, and unloading from the other, so they are a “Zero Footprint” design.

Interestingly, pre-cooling in 20% less time, not only improves the quality and shelf-life of the produce, it also reduces the capital cost per unit throughput of pre-cooling itself.

We are here to help you ripen better, and make more money doing it, with a much more foolproof process.

We also have the best precoolers in the world.  Ask us about them!

Ask us questions:

Or surf to our websites:, or

There are also seasonal relocatable pre-coolers available.

And SmartAit Ripening trailers.

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Air Requirements of Ripening

Banana ripening airflow, and cooling requirements, are a little-understood “art”.

But there is a science to it…we will try to explain.

Most fruit have a specific heat of 9/10th’s of a BTU per pound. We use 1 BTU/pound as the cooling requirement (sometimes, like with avocados, for the heating too,) to be safe.

So, if you want to be able to cool your fruit by 1-degree (F) per hour, and you have 40,000 pounds of it, you need 40,000 BTU’s/hr of cooling capacity, plus extra loads for fan motors and other heat contributions, so we use a factor of 2-times, and say that we need 80,000 BTUs/hr for the task.

Airflow at static pressure is a little more tricky. It is almost impossible to predict how a commodity and packaging and palletization will react to airflow pressures, but there are some guidelines we can suggest.

For pressurized ripening, there are both tarp and tarpless systems. As a general rule of thumb, tarp systems need less airflow at higher static pressure (because the tops of the pallets are sealed off), and tarpless designs need more airflow at lower static pressure (because more air leaks out the tops of the pallets).

For tarp systems, we like 1,000 cfm per pallet, at 0.6″ water column static pressure.

For tarpless designs, we like 1,500 cfm per pallet, at 0.4″ static pressure.

In most cases, larger diameter fans can produce more cfm at higher static pressure, than can smaller diameter fans.

Do you have a ripening room or precooling need?  Please contact us for a free consultation and proposal., or

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All You Ever Wanted to Know about Banana Ripening



Bananas and other unripe fruit (e.g. mango, papaya, avocado, tomato, stone fruit), are ripened in specially constructed rooms by exposure to a controlled atmosphere containing ethylene gas at a concentration of typically 100-200ppm (0.01% to 0.02% by volume in air). The ethylene is introduced from pressurized cylinders, or cartridges or a catalytic generator.

Ethylene obtained from cylinders is often at a higher level, up to 1000ppm (0.1%) since it is a one shot injection and more ethylene is introduced to compensate for room leakage. If ethylene generators are used, the maximum achievable concentration is in the order of 400ppm (0.04%) in a free space of 100m3.

The generators have the added advantage of producing ethylene gas continuously, which maintains gassing levels high enough to support ripening, even if there are air leaks from door gaskets and leaky room construction.

If the introduction of ethylene is uncontrolled there is a risk that the ethylene may reach or exceed the lower explosive limit (LEL) of 3.1% and be ignited by unprotected electrical apparatus or gas heating systems or other incendiary sources, resulting in a fire or explosion.
There are also potential acute risks from oxygen depletion and from the accumulation of other gases such as carbon dioxide; these health risks are exacerbated by the enclosed nature of the process.

Special sensors, for ethylene and carbon dioxide, are available, and better manage the process, for reduced costs, more consistent ripening results, and operator safety.

The main hazards arise from flammable or asphyxiating atmospheres being created by admitting excess ethylene gas into the room. Therefore, the use of cylinders of pure ethylene is strongly discouraged. Ethylene generators are the preferred option. If cylinders of pure ethylene are in use, they should be located outside in a safe well-ventilated position and be fitted with a pressure regulator and flow-meter, and be automatically timed so that the concentration of ethylene in the room does not exceed 25% LEL (7,000 ppm).


A typical ripening procedure for bananas is as follows:

1) Green bananas in cartons and at a fruit pulp temperature of around 14oC are loaded into the ripening room (lower temperatures can damage the fruit).

2) The room is closed and heated for 12-16 hours until the pulp temperature reaches 15-17oC.  This temperature is controlled and maintained by a thermostat. During summer conditions, a refrigeration system will cool the room to maintain the set temperature and  remove the heat of respiration, and the other cooling loads from fan motors and conduction.

3) Ethylene is supplied into the room at a concentration of around 100-400ppm (0.01 – 0.04%). The room is then kept closed for 24 hours. The ethylene acts as a catalyst initiating the hormonal process of ripening.

4) At the end of this time the room is ventilated to clear the ethylene gas and the carbon dioxide released during the initial ripening phase.

5) The room is then closed again and the atmosphere controlled at 17oC reducing to 15oC over three or four days. During this process gases, including carbon dioxide, are evolved in substantial quantities. Most of these gases would normally be vented off by ripening room operators to maintain the carbon dioxide level below 1%, as carbon dioxide levels exceeding 2% inhibit further ripening.

6) The room is finally ventilated and the ripe fruit removed. A common way of ventilating involves opening the doors for at least five, and usually fifteen, minutes before entry is made. Extractor fans may also be used.


Ethylene gas may be produced by one of the following three methods:

1) Ethylene generators which use a catalytic process to produce pure ethylene gas from a solution containing mainly ethyl alcohol (ethanol) but which may have trace quantities of other ingredients (e.g. methanol).

The solution (sometimes known as ‘ripening fluid’) is poured into a reservoir on the ethylene generator where it is slowly fed to an internal heater which vaporizes the ethanol which then passes to the catalytic converter. Each liter of solution produces about 0.33-0.4 m3 of ethylene gas. For the purposes of risk assessments the higher figure should be used.

2) Ethylene cartridges containing approximately 51g of pure ethylene (0.044 m3 at 20oC). Using the appropriate number of cartridges controls the ethylene concentration in the room simply and accurately. Ethylene is released by piercing the cartridge with the tool supplied.

3) Ethylene and ethylene/nitrogen cylinders. Bulk cylinders may be used containing either pure ethylene or a mixture of 5% ethylene in nitrogen (properly used, such a mixture can reduce the explosion risk).  It should be noted that use of ethylene/nitrogen mixture, is the most expensive method.

5 Whichever method is used, the dutyholder should ensure that there are adequate means of dispersing the ethylene gases throughout the ripening room on its release.


The hazards from this process fall into two main categories:


1) Introduction of pure ethylene gas from cartridges may result in localized and short-lived flammable gas/air mixtures.

2) Extensive flammable gas/air mixtures may result from the uncontrolled addition of ethylene from a large cylinder or multiple discharges of cartridges.

3) Formation of flammable gas/air mixtures may result from spillage of ethanol-based solution used in ethylene generators.

4) Incidents to date show that the main acute hazard from this process is the combustion and explosion of excess quantities of pure ethylene resulting from uncontrolled discharges from large capacity cylinders, although other scenarios are possible.
Toxicity and asphyxiation

5) Oxygen deficiency in the room may result from excess addition of ethylene or ethylene-nitrogen mixture from cylinders.

6) The evolution of carbon dioxide during the fruit ripening process may result in a toxic or asphyxiating atmosphere. For example high levels of carbon dioxide may cause loss of consciousness and death from respiratory failure. Other effects such as headache and
exhaustion occur at much lower exposure levels.

7)  All exposures to carbon dioxide should not exceed 0.5% or 1.5% time weighted over an 8-hour or 15-minute period respectively.

8) Ventilation is a key factor both for controlling the process conditions and for ensuring a safe environment. The ripening room should be thoroughly ventilated between loads. As natural ventilation (i.e. open doors or vents) is unpredictable and unreliable, it can only be used with a safe system of work, which will involve the provision of permanent or portable oxygen meters to check the atmosphere before entry.
Mechanical ventilation is to be expected. Ventilation should be used to eliminate acute risks and adequately control other non-acute health risks e.g. exposure to excess levels of carbon dioxide.

Personal monitoring should be carried out as required to ensure that exposure is adequately controlled.


No naked flames (e.g. gas fired heating systems) or other ignition sources should be allowed in the room after introduction of ethylene, until thorough ventilation has taken place, and it has been verified that the ethylene concentration is below 25% of the LEL.


Storage arrangements should ensure that:

1) quantities stored are as small as reasonably practicable;

2) a competent person is responsible;

3) no naked flames, smoking or other ignition sources are permitted near storage areas;

4) full and empty cartridges are stored in a safe, suitably ventilated area preferably in open air;

5) ethanol based solution for ethylene generators is stored in a suitable fire resisting bin or cabinet (quantities of up to 50 liters) which may be indoors. The storage of flammable liquids in containers’ gives further guidance, including arrangements for larger quantities.

More info:

Contains public sector information published by the Health and Safety Executive and licensed under the Open Government Licence v1.0

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The Unrealized Dangers of Carbon Dioxide Accumulation During Fruit Ripening

Ripening rooms, especially when gassing with ethylene, can reach extremely high levels of  carbon dioxide (CO2).  In a test in Seattle, WA, in 2005, CO2 in a ripening room was measured at 10%.

As bananas – and other tropical and subtropical fruit – ripen, they consume oxygen, and emit carbon dioxide and water vapor.  This is, in a way of thinking, the opposite of photosynthesis, where growing plants use sunlight and consume CO2, and emit oxygen.  (A little known fact, is that at night green plants consume oxygen and emit CO2.)

The other fruit which are ripened commercially, include avocados, tomatoes, mango, papaya, and others.

In fruit ripening, each molecule of CO2 produced, replaces one molecule of oxygen consumed.  So if CO2 rises to 5%, for example, oxygen falls by 5% too (from 21% normal air, to 16%, in this example.)

CO2 affects humans in a number of ways and as the table below shows levels as low as 2% have a significant effect on our bodies.

Click here for more info.

A CO2 sensor can help protect the health and safety of ripeners.

Carbon dioxide effects on humans, at increasing levels.

1000ppm 0.1% Prolonged exposure can affect powers of concentration
5000 ppm 0.5% The normal international Safety Limit
10,000ppm 1% Your rate of breathing increases very slightly but you probably will not notice it.
15,000ppm 1.5% The normal Short Term Exposure Limit.
20,000ppm 2% You start to breathe at about 50% above your normal rate. If you are exposed to this level over several hours you may feel tired and get a headache.
30,000ppm 3% You will be breathing at twice your normal rate. You may feel a bit dizzy at times, your heart rate and blood pressure increase and headaches are more frequent. Even your hearing can be impaired.
Now the effects of CO2 really start to take over. Breathing is much faster – about four times the normal rate and after only 30 minutes exposure to this level you will show signs of poisoning and feel a choking sensation.
You will start to smell carbon dioxide, a pungent but stimulating smell like fresh, carbonated water. You will become tired quickly with labored breathing, headaches, tinnitus as well as impaired vision. You are likely to become confused in a few minutes, followed by unconsciousness.
Unconsciousness occurs more quickly, the higher the concentration. The longer the exposure and the higher the level of carbon dioxide, the quicker suffocation occurs.
You will start to smell carbon dioxide, a pungent but stimulating smell like fresh, carbonated water. You will become tired quickly with labored breathing, headaches, tinnitus as well as impaired vision. You are likely to become confused in a few minutes, followed by unconsciousness.
Unconsciousness occurs more quickly, the higher the concentration. The longer the exposure and the higher the level of carbon dioxide, the quicker suffocation occurs.

We are here to help you ripen better, and make more money doing it, with a much more foolproof process.

We also have the best precoolers in the world.  Ask us about them!

Ask us questions:

Or surf to our websites:, or

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The Facts on Avocado Ripening

Avocado ripening is much different than banana ripening.
A lot has to do with the resistance to airflow, of the packaging and fruit.
A lot more has to do with the temperature extremes of avocado ripening, as opposed to bananas.
Bananas, you never want to get hotter than 65F, and never colder than 55F.
Avocados, you can get as hot as 70F, and as cold as 40F.
So, how do banana ripening rooms have to be changed, to do the best job with avocados?
Obviously, you need to run colder refrigerant temperatures, and have more heating capability.  All room providers know this.
What most of them haven’t figured out yet, is that you also need more airflow – or better yet, reversing airflow – for temperature and firmness uniformity across the pallet.

Can you believe, that many operators ripening avocados, take the pallets out of the room and turn them 180-degrees, and put them back in again, to even out the ripening / firmness.

There is a better way, and we have it.

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Fire away with your questions!

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