With today’s advancements in food preservation, industries, hospitals or homes are adopting cost-effective, reliable and efficient technologies.
With the food freeze dryer, it has become easy to store food safely and in good quality for future use.
Food in freeze dryer
- What is Food Freeze Dryer?
- History of Food Freeze Drying Technology
- Benefits of Freeze Drying Food
- Problems with Freeze Drying Process
- Types of Freeze Dryer Equipment
- Key Methods in Food Freeze Dryer Equipment
- Main Components of Food Freeze Dryer Equipment
- How Food Freeze Dryer Works –The Principle of Freeze Drying
- How to Optimize Efficiency of Food Freeze Dryer
- Food Dehydrator vs. Food Freeze Dryer
- Comparison between Freeze Dryer and Conventional Dryers
- How to Extend the Life of the Vacuum Pump Oil in Food Freeze Dryer
- Uses of Industrial Food Freeze Dryer
What is Food Freeze Dryer?
Food freeze dryer is a machine that stores and preserves high-quality food by dehydrating food content.
The machine operates at low temperature and high pressure.
It uses a process known as the lyophilization.
Through this process, it lowers the temperature of food to be preserved.
Lyophilization involves removing water, mostly from the perishable fruits to extend their life or to make transportation easier.
Lyophilization – Photo courtesy: Jyothsna
The machine freezes the food by reducing the food pressure and adjusting its heat content to make the frozen water sublime.
Therefore, the machine is essential in preserving the perishable food products.
It retains the physical structure of the food and maintains it for rehydration in the later dates before consumption.
History of Food Freeze Drying Technology
The history of food freeze drying technology dates back to the 15th century when the Incas used rudimentary forms of freezing drying.
Freeze drying – Photo courtesy: Labo Gene
They preserved their crop products on the top of mountains above the Machu Picchu which have a low temperature to freeze them.
The mountain top was as well associated with low pressure.
With the lower air pressure on the high altitudes of the mountains, water inside the crops vaporized slowly.
Notably, modern food freeze drying technology was developed during World War II.
Besides, this technology was used to refrigerate blood being ferried to Europe from the United States for medical treatment of wounded fighters.
This was to mitigate the problem of blood getting spoilt in transit.
Afterward, the technology grew as a commercial method of translating blood into a stable and viable chemical compound.
There was, therefore, no need for refrigeration.
The technique became popular in the national aeronautics and space administration.
It was used in the making of freeze-dried ice cream, which was the food for the astronaut.
Freeze drying technology was after that applied to penicillin and bone.
This made it gain recognition as an essential technique, suitable for the preservation of various biologicals.
This preservation technique is widely used, in pharmaceuticals, ceramics, food, restoration of water-damaged materials, among other many functions.
The dried foods are always preserved in such a way that their structure and chemistry is close to their natural composition.
This assures that the nutrients and the vitamins of the food preserved are well maintained.
The freeze drying technology is as well used in producing the essence of even to additives like the flavors.
Benefits of Freeze Drying Food
The freeze drying of food has a lot of benefits.
It is always regarded as the optimal technique for dehydration purposes because of the quality preservations it provides.
Food freeze drying system
Let us briefly explore the essential benefits of freeze drying food.
a) Shelf-life Extension
The lowering of temperatures, together with the quick water transition through sublimation helps to achieve a longer shelf life.
It means the quality of the food preserved is as well maintained for a more extended period than usual.
The incorporation of proper packaging and storage conditions help to increase the shelf life further.
Freeze dried food products are of low quality when not correctly or fully re-hydrated.
Food Freeze Dryer provides complete rehydration to the food preserved.
This, therefore, signifies an excellent quality of the food products when consumption time comes.
c) Maintenance of Nutrients and Sensory Quality
Food Freeze Dryer provides minimum deterioration reactions because it happens in low temperatures.
This ensures the retention of the nutrients and other qualities of the food like the color.
The original structure and shape, and the soft, crispy texture characteristics of the food are also well preserved.
d) No Addition of Preservative Chemicals
There is no chemical added to the products being preserved, and they are simple to reconstitute by adding water.
e) Freeze Drying makes Food More Palatable
The end result after dehydration of the products is done is always either withery or sometimes crunchy and hard.
If the products are freeze-dried, then once in the mouth, they become soft.
f) Weight of Food is Reduced
Lyophilisation eradicates about 98 percent of water from the food, thus reducing the weight of the food.
This is of great benefit to individuals who have to carry their food for days or months before consuming it.
g) Makes Preserved Food Easier to Prepare
Freeze-dried foods are easier to prepare by only adding hot or cold water, and the food is ready for consumption.
However, it might take longer when cold water is used.
When compared with the dehydrated food, their preparation will take a shorter time as compared to the freeze-dried food.
In most cases, the latter will require seasoning, which takes time.
Freeze drying enables customization to the unique requirements and the targets of the user.
The ingredients of the freeze-dried food can be cut into various distinctive shapes and sizes.
Finished products can as well be mixed into any formulation for complete flavor profile leading to a unique end product.
Other benefits obtained from the use of the freeze drying machine include
- Creation of pores
- Little damage to the heat-labile materials
- The process of freeze drying does not always result in shrinkage or toughening of the food product being dried
Freeze drying equipment is, most of the time essential when the products meet the following criteria.
- When the product is unstable
- The product is expensive
- Frozen storage is inappropriate
- When complete and quick dehydration is needed
- When there is a need for minimizing the weight of the product.
Problems with Freeze Drying Process
Despite the immense benefits of the freeze drying machine, it also has some problems.
Some of the major challenges are:
Inserting food in freeze dryer
The equipment required for freeze drying is more costly than the other available options.
This makes it not a suitable choice when the value of the product being processed does not correspond to the costs.
The cost of the freeze drying process may vary depending on many factors.
These factors include:
i. Nature of the product being processed
ii. Processing capacity
iii. Packaging material
The cost of the process can also increase depending on the type of energy used.
· Leakage of Silicone Oil
The freeze drying process involves the use of fluids to cool or heat the shelves in the freeze dryer.
Continuous cooling and heating process can result in the leakage of silicone oil at the shelf and weakly connected horse joints.
This can result in a great loss because the product being processed may be contaminated.
However, a spectrometer is usually used to examine vapor release by the silicon oil for corrective measures to be taken.
This helps to protect the products from contamination.
Other challenges include:
- Sensitivity, complexity of products.
- Destabilization of the structure of the proteins and even fusion of liposomes. Thus may occur when the hydration shell is removed from the products in the absence of suitable stabilizers.
- Destabilization can be as a result of extremely low content of water in the final product. Therefore, to avoid the problem, the optimal content of water in the final product should be determined.
- The structure of the product may be altered and destroyed when excess heat is applied in the freeze drying process. Therefore, there is need to take caution to avoid the use of excess heat during the process.
- Only selected foods can be freeze-dried. Not every product and food type can withstand the process of freeze drying.
Besides, the process may not be cost-effective for some products, especially some meat and fruits.
Some products cannot endure the process and may end up getting destroyed.
- Large products may take longer to dehydrate. This is owing to the large amount of water content they have.
- Storage problems can also result from the products that have been dehydrated from the freeze drying process. This is because, during the process, the original size and shape of the products may not be preserved.
It, therefore, means that extra storage space will be required as compared.
- If not stored correctly, freeze-dried food can still spoil. The storage of such food, therefore, needs moisture-tight and air-tight containers like bags or cans.
The products also have to be appropriately preserved because they are always very fragile and can easily crumble if not stored and handled with care.
Types of Freeze Dryer Equipment
Freeze dryer equipment come in various types.
This is because of its adverse application in diverse industries.
Some of the types of freeze dryer equipment are as discussed below.
Food freeze drying process
1) Conductive Freeze Dryer
This type of freeze dryer uses the conduction principle to dehydrate the products.
The food or products to be dehydrated are placed on the trays which rest on the heater plates.
Also, the slow drying process then begins, where heat is transferred to one side of the food by conduction.
Moreover, heat transferred is then used to dehydrate the food by vaporizing the water content
2) Contact Freeze Dryer
The contact freeze dryer works with the same principle as the conduction freeze dryers.
Once the food substance comes into contact with the heater plates through the contact of the trays, drying happens.
This is possible because heat is transferred to the food or product being processed.
Thus the product is able to dehydrate due to the exposure to heat.
3) Accelerated Freeze Dryer
Accelerated freeze dryers also use the conduction principle.
The food is held in between the two layers of the metal mesh, which has been expanded.
Pressure is then subjected to both sides of the product.
In this case, the mesh enables a more rapid transfer of heat into the product than the solid plates.
Therefore, vapor can easily escape from the food surface.
4) Irradiation Freeze Dryer
This type of freeze dryer uses the ionizing energy or radiation to dry the food products.
When applied in small amounts, it increases the shelf life of the products.
Most scientists have argued that irradiation of food is the most effective and safest form of food processing.
That explains why it is the most commonly used freeze dryer in most countries.
The type of radiation used in this case differs from the radioactive fallouts that may result from nuclear accidents.
Also, the radioactive sources used in the equipment do not produce gamma, x-rays, or electrons that can make the products radioactive.
After drying is complete, there is no radioactive energy that remains in the food.
Normally, the operation of the irradiation freeze dryer entails exposure of the product to the ionizing radiation.
These radiation rays share some similar characteristics with the microwaves, although they have higher penetration and higher energy.
The rays then penetrate the food like in a microwave though the food does not heat up as much. Any organisms that may poison the food products are killed.
Also, the products are dehydrated when the rays pass through the product.
The irradiation freeze dryer is also considered the best equipment because it also removes food poisoning.
5) Microwave and Dielectric Freeze Dryer
This type of freeze dryer uses the radio frequency heater to dry the products.
The heaters can be used in freeze drying, though that is not very common.
This is because it is difficult to control since water gets heated faster compared to ice.
6) Radiation Freeze Dryer
In this type of freeze dryer, infrared radiation from the radiant heater is used.
The radiation heats the shallow layer of the products on the flat trays.
Furthermore, the product dries uniformly because the heating is more uniform compared to the conduction types.
Key Methods in Food Freeze Dryer Equipment
In food freeze drying, there are three major methods that are applied in the preservation of the products.
Food freeze drying graph
· Manifold Freeze Drying Method
In this method of food freeze drying, each flask ampule is attached to the ports of the drying chamber.
A freezer can either be used to freeze the products in a temperature bath through direct submersion or freezing by shell.
This depends on the volume and nature of the products to be dried.
To prevent warming, the product is attached to the manifold.
A vacuum is made in the container of the product to avoid low temperature in the system.
The method is suitable for smaller volumes of products that have collapse temperature.
The method is considered better than batch freeze drying method.
Every vial has a direct path to the connector because the vessels are individually connected to the manifold.
This reduces the competition for the molecular space made in the batch system.
The proximity to the collector creates an environment which maximizes drying efficiency
However, this method also has its weaknesses.
Exposing the vessels to ambient temperature may affect the heat input.
The manifold drying method is not suitable for products with precise temperature control.
· Batch Freeze Drying Method
In this method, similar products are placed together in the tray dryer.
Pre-freezing of the products is usually done on the shelf of the tray dryer.
The temperature and the amount of the product can be maintained during the drying process.
Slight variation in the heat input may be felt at some points in this method.
Also, the clear door can as well radiantly heat the vial that is located next to it.
Therefore, a small variation in the residual moisture may result due to the variations in the system.
Under the same atmospheric conditions, batch drying allows the vials to be closed at the same time.
There is a need to ensure a uniform environment in the vial and uniformity in the stability of the product during storage.
To achieve this, the vials should be stopped in the vacuum.
This is only achievable when the stoppering of the vials happens at the same time.
You can, therefore use this method to prepare large amounts of the vials or the ampules of a single product.
· Bulk freeze drying method
This method is done on the tray dryer like the batch drying.
However, in this method, the product is dried as one unit after it has been poured into a bulk pan.
The products are spread in the entire surface area of the shell.
They may be in the same size as the products dried in vials.
There are no empty spaces within the mass of the product, so it is possible to alter the heat input.
The input heat is limited to that offered by the shell as a result of the contact with the products.
Under controlled conditions, the bulk drying does not seal the product like the manifold and batch methods.
Besides, the products in the bulk freezer are always packaged in airtight containers prior to their removal from the freeze drying system.
The method is suitable for products that are not highly sensitive to moisture or oxygen.
Main Components of Food Freeze Dryer Equipment
A food freeze dryer equipment is composed of various components, each performing a specific function.
Below are some of the main components.
This part of the component, made from stainless steel, is polished with insulation inside.
It has various shelves that help it to hold the products.
To ensure that the door is vacuum-tight when it is closed, a hydraulic or sometimes an electric motor is used.
b) Process Condenser
This part of the dryer has the refrigerated coils that can either be placed internally or externally to the chamber.
The function of the condenser is to trap water during the drying process.
Section of the condenser
During the primary drying process, the temperature of the condenser should be lower than that of the product, at around 200C.
This increases the efficiency and ensures that the required amount of water vapor is fully condensed.
c) Shelf Fluid
During the primary and the secondary phases of drying, an external changer controls the amount of heat (silicon oil).
To achieve this, a pump distributes silicone oil around the system.
d) Refrigeration System
The system uses the liquid nitrogen or sometimes compressors to cool the shelves.
This will then supply energy that is needed for the freezing of the product.
e) Vacuum System
In this part of the equipment, a vacuum of 50-100 microbar is used during the drying process.
This helps to eradicate the solvent.
The application of the vacuum makes the use of a two-stage rotary vacuum pump.
Large chambers require the use of multiple pumps.
Using a condenser, the system is able to compress any non-condensable gas.
f) Control System
This part controls the values of shelf temperature and other values like the time, which is dependent on the product.
It also controls other processes in the freeze dryer equipment.
How Food Freeze Dryer Works –The Principle of Freeze Drying
The fundamental principle of freeze drying is sublimation, which refers to the change of state from solid to gas directly.
It happens when the molecules of a substance gain energy that breaks the bonds existing between them.
The physical state of the substance mainly depends on atmospheric pressure and temperature.
Moreover, the pressure and temperature have to be within a specific range for a substance to take a particular state.
Working of the Freeze Dryer
The operation of the freeze dryer involves the three major stages, as discussed below.
As the name suggests, this stage involves the freezing of the product.
Cooling the product to below its eutectic point enables sublimation.
Eutectic point is the lowest temperature at which liquids and solids of any element coexist.
The freezing stage is always a critical point during the freeze drying process.
If wrongly done, the products may be spoilt.
Large products may take a longer period to freeze dry.
· Primary Drying
This stage sees reduced pressure provision of optimum heat for the water content in the product to sublime.
Using the latent heat of sublimation of the product’s molecules, you can calculate the amount of heat required.
Applying excess heat may alter the structure of the product.
This explains why this stage is always slow.
The partial vacuum controls the pressure during the process.
Also, the rate of sublimation is raised by the vacuum, thus making it a deliberate drying process.
· Secondary Drying
This stage aims to eliminate the unfrozen molecules of water because ice molecules had been removed in the primary drying stage.
The adsorption of isotherm materials regulates this stage of the freeze drying process.
Here, the temperature is higher when compared to the primary stage.
This helps to break down the physiochemical interaction, which may have formed in between the frozen molecules and the water molecules.
It is also here that desorption happens when the temperature is lowered.
After the freeze drying is complete, the inert gas is used to break the vacuum before the sealing of the products.
The end amount of water is always low at the end of the process, about one to four percent.
How to Optimize Efficiency of Food Freeze Dryer
There are several factors that usually affect the efficiency of the food freeze dryer.
Below are some of the measures that can be taken to optimize the efficiency of the equipment.
Increasing the surface area of the product- the larger the surface area of the frozen material, the higher the efficiency of the food freeze dryer.
Reducing the thickness of the product- the thicker the product, the lower the effectiveness of the food freezer dryer.
Freeze dried food
This is because the thickness reduces its ability to absorb and transfer heat during the sublimation process.
· Reduced Eutectic Temperature
A lower eutectic temperature will optimize the efficiency of the food freeze dryer by reducing the time taken for the product to dry.
· Adjusting the Condenser Temperature
Optimization of the efficiency of the freezer dryer is attained by this temperature as dictated by the freezing temperature and the collapse temperature of the material.
Optimization of the efficiency of the freeze dryer takes place when the fully frozen product is placed in the deep vacuum.
Food Dehydrator vs. Food Freeze Dryer
These two machines have many clear differences that you should be versed with when choosing the right machine.
The differences are evident in the following aspects.
· The End Product
The composition of the food products from the food freeze dryer weighs lower as compared to the food from the food dehydrator.
Also, the food products from the freeze dryer are softer compared to those from the food dehydrator.
· Product Appearance
In food dehydrator, the appearance of the products is always squished.
On the other hand, the product will always retain its structure, although the size reduces.
The moisture content eliminated by the two methods differs even though both are used to remove the water content.
Besides, the food dehydrator eliminates up to about 95% of the moisture content from the product while food freeze dryer eliminates about 99%.
Products preserved using the food dehydrator are cheaper as compared to those preserved from the food freezer dyer.
Comparison between Freeze Dryer and Conventional Dryers
Section of food freeze dryer
- The freeze dryer works by lowering pressure and temperatures and freezing the product. On the other hand, conventional dryers use heat to evaporate the water content from the products.
- Conventional dryers depend mostly on the convective and conductive methods, making the end product to have lower and poor quality. It is also characterized by high chances of contamination.
Using a freeze dryer, the end products are of a higher quality because the nutrients of the products are preserved. The products are also safe.
- Conventional dryers use the product belt by passing the air inside the dryer to eliminate the moisture content. In freeze dryer, the product is placed inside the equipment after which lower energy is applied to the food. The moisture content in the product, therefore vaporizes.
How to Extend the Life of the Vacuum Pump Oil in Food Freeze Dryer
Small amounts of water will always trickle into the vacuum pump when it runs.
To remove the water before starting a new batch of food, open the valve of the oil drain located on the vacuum pump.
When doing this, a small amount of oil will also drain out.
After closing the drain valve, add a new amount of pump into the vacuum pump.
This helps to replace the drained oil, thus increasing the lifespan of the vacuum pump oil.
When to change the vacuum pump oil
When food batches start taking longer than usual to process, then it is time to change the pump oil.
You can also look at the glass window.
When the oil has visible particulates, looks milky or amber in color, then it’s time to change it.
When the oil spurts from the vacuum pump, then the following maybe some of the reasons.
The system might be experiencing substantial leakage.
This may occur if the drain valve was left open or if the door is not clean.
The oil may also spurt because of a rise in its level as a result of vacuum hose adding moisture therein.
Again, it may spurt because of the trapped oil in the cartridge of the pump.
This may occur if the vacuum pump was shut off.
Uses of Industrial Food Freeze Dryer
Some of the essential applications of the food freeze dryer in the industry are:
· Pharmaceutical Industry and Biotechnology
The pharmaceutical industry depends on the freeze drying equipment to increase the shelf life of pharmaceutical products like medicine.
After freeze drying, the materials are sealed in vial materials for easy shipment.
And more importantly, you must choose the best pharmaceutical packaging solution for your products.
It is the only way to ensure your products remain contamination free.
· Food Industry
Freeze drying equipment can also be used in the preservation of food and making it light by reducing the weight.
A typical example of this is freeze-dried cream ice.
· Technological Industry
The freeze dryer is used in the synthesis of chemicals.
This is done by lyophilizing the products to make them stable or easier to dissolve in water for subsequent application.
The equipment can also be used in the late stage of purification in the bio-separations.
This is because it can effectively remove the solvents.
From this guide, you are now well equipped with the characteristics and functioning mechanism of the freeze dryer.
You can now make well informed decisions on how to preserve your food well and efficiently.
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