Pre-cooling

Summary

The video script delves into the critical process of pre-cooling for preserving the quality of fresh fruits and vegetables post-harvest. It highlights how pre-cooling removes field heat to extend shelf life, reduce respiration rates, and limit ethylene production, thereby inhibiting ripening and microbial growth. The script outlines four main pre-cooling methods: cold air cooling, hydrocooling, top icing, and vacuum cooling, each with its advantages and disadvantages. It also discusses considerations such as produce size, temperature, packaging, and flow rate, emphasizing the importance of selecting the right method for different types of produce to ensure optimal freshness and marketability.

Takeaways

• 🧊 Pre-cooling is the process of removing field heat immediately after harvest to preserve the quality of fruits and vegetables.
• 📉 Field heat accelerates the deterioration of produce and reduces shelf life, making pre-cooling crucial for maintaining fresh and marketable products.
• 🌡 Pre-cooling helps to extend the shelf life of fresh produce by lowering the temperature to optimal storage levels.
• 🌿 Storing produce at cold temperatures with appropriate humidity protects them from decay and bacteria, further extending their selling period.
• 🔁 Low temperatures reduce the rate of cellular respiration, slowing down the ripening process and preserving the freshness of the produce.
• 💨 Pre-cooling also reduces ethylene production, a plant hormone that induces ripening and can lead to faster spoilage.
• 🚫 Colder temperatures inhibit the growth of microorganisms, which helps to keep the produce fresh for a longer time.
• 📏 Factors to consider in the pre-cooling process include the size of the produce, initial and final temperatures, packaging, and flow rate.
• 🛠 There are four main pre-cooling methods: cold air cooling, hydrocooling, ice cooling, and vacuum cooling, each with its advantages and disadvantages.
• 🌬 Cold air cooling involves slow heat transfer by convection and is suitable for products with a longer storage life and those marketed soon after harvest.
• 💦 Hydrocooling involves water contact and can be done through showers, sprays, or immersion, providing rapid cooling and the ability to clean produce.
• ❄️ Ice cooling, including top icing or ice slurry, offers rapid heat transfer and prevents moisture loss but requires additional drying and monitoring.
• 🌀 Vacuum cooling rapidly and uniformly cools produce by reducing atmospheric pressure, suitable for leafy vegetables but with risks of wilting and high costs.

Q & A

What is the purpose of pre-cooling in post-harvest handling of fruits and vegetables?

Pre-cooling is the process of removing field heat immediately after harvest to preserve the quality of fruits and vegetables, extend their shelf life, and maintain them in a fresh and marketable state.

Why is it important to remove field heat quickly after harvest?

Field heat accelerates the deterioration of produce and can lead to faster spoilage. Removing field heat promptly through pre-cooling helps to slow down these processes and maintain product quality.

How does pre-cooling affect the shelf life of fresh produce?

Pre-cooling extends the shelf life of fresh produce by storing it at cold temperatures with appropriate humidity levels, which protects fruits and vegetables from decay and bacteria.

What is the impact of low temperatures on cellular respiration in living tissues?

Low temperatures decrease cellular respiration in living tissues. As temperature rises, the kinetic energy required for chemical reactions like cellular respiration increases, leading to more respiration at warmer temperatures.

How does pre-cooling reduce ethylene production in fruits?

Pre-cooling reduces ethylene production by lowering the temperature, which is a gaseous plant hormone that induces the ripening process for many fruits. Lower ethylene levels slow down the ripening process.

What factors need to be considered in the pre-cooling process?

Factors to consider in pre-cooling include the size of the produce (small, medium, large), the initial and final temperature of the product, the packaging method, the flow rate, and the characteristics of the produce such as chilling sensibility or the need for rapid heat removal.

What are the four main methods for pre-cooling produce?

The four main methods for pre-cooling are cold air cooling, hydrocooling, ice water cooling, and vacuum cooling.

How does cold air cooling work and what are its advantages and disadvantages?

Cold air cooling transfers heat from the produce to the cold air circulated around the stacked containers through convection. It is clean, simple, and has low installation and maintenance costs, but it is slow and can lead to uneven cooling, especially not suitable for leafy vegetables due to the risk of dehydration.

What is forced air or pressure cooling and what are its pros and cons?

Forced air or pressure cooling involves passing cold air by force from one side to another using a big fan, leading to rapid and high heat transfer performance. It is clean, simple, and has low installation and maintenance costs, but it can cause desiccation of the crop if not managed properly.

Can you explain hydrocooling and its benefits and drawbacks?

Hydrocooling involves showering the commodity with cold water, which can be in bins, boxes, or on a conveyor belt. It offers rapid cooling, high energy efficiency, and the ability to clean vegetables with chlorinated water. However, it requires an additional drying step and ongoing monitoring of water quality and cooler cleanliness.

What is top icing and how does it differ from other pre-cooling methods?

Top icing is an old method where a layer of crushed ice is placed directly on top of the produce to reduce field temperature rapidly. It prevents moisture loss but adds weight and can increase the risk of physical injury and rotting if the icing period is prolonged.

How does vacuum cooling work and what are its advantages and disadvantages?

Vacuum cooling reduces atmospheric pressure in sealed chambers, which also reduces the pressure of water vapor, leading to rapid and uniform cooling. It is energy-efficient but carries the risk of wilting due to moisture loss and requires packaging with holes for water evaporation, making it more expensive.

Outlines

00:00

🧊 Pre-Cooling Process and Its Benefits

The first paragraph introduces the concept of pre-cooling, which is the immediate removal of field heat after harvest to prevent the deterioration of fruits and vegetables. It emphasizes the importance of pre-cooling in maintaining the quality and extending the shelf life of produce. The benefits include the reduction of field heat, which is the temperature difference between the harvested crop and the optimal storage temperature. Pre-cooling also slows down the respiration rate of the produce, reduces ethylene production that induces ripening, and inhibits the growth of microorganisms. Factors to consider in pre-cooling include the size of the produce, initial and final temperatures, packaging, flow rate, and produce characteristics. The paragraph also outlines four main pre-cooling methods: cold air cooling, hydrocooling, ice cooling, and vacuum cooling, with a brief introduction to each method.

05:02

🌡 Detailed Pre-Cooling Methods and Considerations

The second paragraph delves deeper into the various pre-cooling methods, discussing their advantages, disadvantages, and suitability for different types of produce. Cold air cooling is described as a common method involving the transfer of heat from the produce to the circulated cold air, suitable for products with a longer storage life. Forced air or pressure cooling is highlighted for its rapid and high heat transfer performance but noted for the risk of desiccation. Hydrocooling is explained in two forms: shower or batch type and immersion type, each with its benefits such as rapid cooling and the ability to clean vegetables, but also with the need for additional drying and water quality monitoring. Top icing is mentioned as a method involving the application of crushed ice or ice slurry to reduce field temperature, with advantages like rapid cooling but also potential disadvantages like increased weight and risk of physical injury or rotting. Lastly, vacuum cooling is described as a method that involves reducing atmospheric pressure to facilitate cooling, offering rapid and uniform cooling but with the risk of wilting and higher costs. The paragraph concludes with a list of crops suitable for each cooling method.

Keywords

💡Pre-cooling

Pre-cooling is the process of removing field heat from produce immediately after harvest. It is crucial for preserving the quality of fruits and vegetables, as field heat accelerates deterioration. The term is central to the video's theme, which revolves around maintaining the freshness and marketability of produce. For instance, the script discusses the importance of pre-cooling in extending the shelf life and reducing the rate of respiration in produce.

💡Field Heat

Field heat refers to the temperature of a crop at the time of harvest. It is significant because it affects the rate of deterioration and the quality of the produce. The video emphasizes the need to remove field heat through pre-cooling to ensure that fruits and vegetables remain fresh and marketable. An example from the script is the difference in temperature between a berry harvested at 22°C and the optimal storage temperature of 1°C.

💡Shelf Life

Shelf life is the period during which a product remains fresh and suitable for sale. The video highlights pre-cooling as a method to extend the shelf life of produce by slowing down the rate of respiration and decay. The script mentions that storing produce at cold temperatures with appropriate humidity levels helps to protect them from bacteria and decay, thereby extending their selling period.

💡Respiration Rate

Respiration rate in the context of the video refers to the cellular respiration in living tissues of fruits and vegetables. The script explains that low temperatures decrease cellular respiration, which is a chemical reaction that occurs more rapidly at warmer temperatures. By pre-cooling produce, the respiration rate is reduced, helping to preserve freshness.

💡Ethylene

Ethylene is a gaseous plant hormone that induces the ripening process in many fruits. The video discusses how pre-cooling can reduce ethylene production, which in turn slows down the ripening process. This is important for maintaining the quality and extending the shelf life of produce, as an unripe fruit generally has low levels of ethylene.

💡Microorganism Growth

The growth of microorganisms is a factor that contributes to the spoilage of fruits and vegetables. The video script mentions that colder temperatures inhibit the growth of both existing and new microbes on produce. This is an important aspect of pre-cooling, as it helps to maintain the freshness and quality of the produce by limiting microbial activity.

💡Cold Air Cooling

Cold air cooling is one of the four main pre-cooling methods discussed in the video. It involves the transfer of heat from the produce to the cold air being circulated around the stacked containers. The script describes this method as common and widely used, especially for products with relatively long storage life that are marketed soon after harvest.

💡Hydrocooling

Hydrocooling is another pre-cooling method mentioned in the video, which involves using cold water to cool the produce. The script explains different types of hydrocooling, such as shower, spray, and immersion, each suitable for different types of produce. This method is advantageous for its rapid cooling and ability to clean vegetables, but it requires additional steps for drying and monitoring water quality.

💡Top Icing

Top icing is a pre-cooling method where a layer of crushed ice is placed directly on top of the produce to reduce field temperature. The video script also mentions the use of an ice slurry to lower the melting point of the ice. This method is beneficial for its rapid heat transfer performance but comes with the disadvantage of adding weight from the ice and the potential for physical injury or rotting of vegetables.

💡Vacuum Cooling

Vacuum cooling is a method where produce is cooled by reducing atmospheric pressure in sealed chambers. The script highlights the advantages of this method, such as rapid and uniform cooling for all vegetables and high energy efficiency. However, it also points out the risks of wilting due to moisture loss and the high cost associated with this method.

💡Chilling Sensitivity

Chilling sensitivity refers to the reaction of certain produce to cold temperatures, which can lead to damage or a decrease in quality. The video script mentions that pre-cooling methods must be chosen based on the characteristics of the produce, such as their chilling sensitivity. This is important to ensure that the produce remains fresh and undamaged during the cooling process.

Highlights

Pre-cooling is essential for removing field heat immediately after harvest to preserve the quality of fruits and vegetables.

Field heat accelerates the deterioration of produce and affects the efficiency of post-harvest systems.

Pre-cooling extends the shelf life and selling period of fresh produce.

Storing produce at cold temperatures with appropriate humidity protects them from decay and bacteria.

Low temperatures reduce the rate of respiration in living tissues, slowing down cellular respiration.

Reduced ethylene production at lower temperatures delays the ripening process in fruits.

Colder temperatures inhibit the growth of microorganisms, preserving the freshness of produce.

Considerations for pre-cooling include produce size, initial and final temperatures, packaging, and flow rate.

Characteristics such as chilling sensibility and the need for rapid heat removal determine the pre-cooling method.

Cold air cooling is a common method where heat is transferred by convection to the cold air circulated around the produce.

Forced air or pressure cooling uses high-velocity air to cool produce more rapidly.

Hydrocooling involves showering produce with cold water, often on a conveyor belt.

Top icing is an old method that involves placing crushed ice directly on top of produce to reduce field temperature.

Vacuum cooling rapidly and uniformly cools produce by reducing atmospheric pressure in sealed chambers.

Cold air cooling is advantageous for its cleanliness, simplicity, and low installation and maintenance costs.

Forced air cooling is rapid and efficient but may cause desiccation if not properly managed.

Hydrocooling is effective for cleaning vegetables and preventing spoilage but requires additional drying and monitoring.

Top icing provides rapid cooling but may add weight and risk of physical injury or rotting to the produce.

Vacuum cooling is highly efficient but carries the risk of wilting and requires special packaging to allow for moisture evaporation.

Transcripts

[Music]

what is

precooling the precooling process is the

removal of field heat immediately

following Harvest where field heat

accelerates the deterioration and

inessence

processes in post Harvest systems

pre-cooling is a crucial step in

preserving highquality fruits and

vegetables and the most crucial of all

the processes required to maintain any

acceptable fresh and marketable fruits

and vegetable

production these are the advantages of

pre-cooling process it removes the field

heat field heat the difference in

temperature between the temperature of a

crop harvested and the optimal storage

temperature of that product X for

example if you harvest a berry at an

ambient temperature of 22° c and the

best temperature for extended Cold

Storage is 1° C your field heat is 21°

C increases the shelf life of fresh

produce storing produce in cold

temperatures with appropriate relative

humidity levels protects fruits and

vegetables from Decay and

bacteria this extends the shelf life

which in turn extends the product's

selling period reduces the rate of

respiration low temperatures decrease

cellular respiration in living

tissues as the temperature rises the

kinetic energy required to engage in

chemical reactions like cellular

respiration goes down therefore warmer

temperatures typically result in more

cellular

respiration reduces ethylene

production ethylene is a gaseous plant

hormone that plays an important role in

inducing the ripening process for many

fruits together with other hormones and

signals an unripe fruit generally has

low levels of ethylene as the fruit

matures ethylene is produced as a signal

to induce fruit ripening limiting of

microorganism growth colder temperatures

inhibit growth of both existing and new

microbes there are things we need to

consider in pre-cooling

process

size small medium large to have a

classification of the

produce

temperature the initial and final

temperature of the product packaging the

way produce is being packaged makes

precooling methods more or less suitable

flow rate products also differ in their

flow capacity the faster products can be

cooled down the better

characteristics characteristics of

produce such as chilling sensibility or

the need for Rapid heat removal method

the methods to be used due to some

produce cannot get in contact with water

there are four main methods for

pre-cooling cold air cooling

hydrocooling SL cold water cooling top

icing vacuum cooling now what is cold

air Cooling we have room cooling heat is

transferred slowly from the mass of the

produce by convection to the cold air

being circulated around the Stacked

containers this is most common and

widely used method here cold air is

passed from the fan and cool by

convection process its commonest use is

for products with relatively long

storage life and marketed soon after

harvest

advantages clean and simple low

installation and maintenance cost

provides temporary storage after

precooling

disadvantage slow uneven cooling at the

beginning not suitable for leafy

vegetables due to prolonged cooling

hours resulting in

dehydration two forced air or pressure

Cooling in this system cold air is

passed by force from one side to other

side using big fan cold air movement is

through the containers rather than

around the

containers air is blown at a a high

velocity leading to desiccation of the

crop to minimize this effect air is

blown through cold water

sprays adequate air flow is

necessary this is because fruits in the

center of packages tend to lose heat at

a slower rate compared to those on the

exterior

advantages clean and simple rapid high

heat transfer

performance low installation and

maintenance cost disadvantage ages

slower as compared to vacuum cooling

these are crops usually precooled by

force hydrocooling SL cold water cooling

we have shower SL batch type the water

showers over the commodity which may be

in bends or boxes or loosen a conveyor

belt a common design is to transport the

crop on a perforated conveyor belt the

speed of the conveyor can be adjusted to

the time required to cool the crop and

cold water is pumped from the tank T and

allowed to fall on the produce in

sprinkled type and then falls through to

the tank below then filtered recycled

and

recooled immersion type it is simplest

type of a hydroc cooler in which produce

is dipped in cold water here product are

normally in bulk is in direct contact

with the cold water as it moves through

a long tank of cold this method is best

suited for products that do not float

because slow cooling would result If the

product simply moved out of the water

Advan an ages rapid High Energy

Efficiency provide means to clean

vegetables EG with chlorinated water to

prevent

spoilage

disadvantages additional step of drying

required additional effort required to

monitor water quality and cleanliness of

cooler daily so these are the crops

normally hydr cooled top icing this is

one of the oldest ways to reduce field

temperature it is commonly applied to

boxes of produce by placing a layer of

crushed ice directly on top of the crop

it can also be applied as an ice slurry

made from 60% finely crushed ice 40%

water and 0.1% sodium chloride to lower

the melting point of the

ice

advantages rapid high heat transfer

performance prevents any moisture loss

from

vegetables disadvantages additional

weight from crushed ice and high water

content from melting ice could increase

the risk of physical injury and rotting

of

vegetables risk of chilling injury to

vegetables if period of icing is

prolonged some of the most crops

suitable for ice cooling vacuum cooling

leafy vegetables are commonly cooled by

reducing atmospheric pressure in

artificial hermetically sealed

Chambers reducing the atmosphere

pressure also reduces the pressure or

water vapor in the the chamber and thus

cooling is affected the outstanding

advantages of vacuum cooling are the

sped and uniformity of cooling of

adapted

Commodities

advantages rapid uniform cooling for all

vegetables high Energy

Efficiency

disadvantages risk of wilting due to

moisture loss high cost requires

packaging with holes for water

evaporation crops suitable for ice

Cooling

beans lettuce mushroom spinach carrots

capsicum celery corn leafy vegetables

[Music]

cabbage