IQF Vs. Traditional Freezing Methods: A Comparative Analysis

Freezing is one of the most widely used methods for food preservation that allows locking texture, nutritional value and taste of food better than other methods. Over the years, different freezing methods have been adopted across industries with the advancement in technology. However, individual quick freezing (IQF) remains the preferred freezing method. 

Let us discover how traditional freezing methods compare with IQF. 

What Is the Need for Freezing

When it comes to the long-term preservation of fruits and vegetables, freezing is considered superior to canning and dehydration. Given the items being preserved are of high quality, GMP or good manufacturing practices are utilised in the preservation process, and the products are kept in the required temperature range, freezing helps extend the shelf-life.  

Additionally, freezing requires the least processing time when compared in terms of cost, quality, and use of energy. Usually, freezing involves reducing the temperature of the product to -18 °C or below. However, dehydration and canning of fruits and vegetables require less energy than the freezing process and storage but the overall costs of freezing can be kept low or lower than other food preservation methods. 

In summary, the benefits of freezing include the following. 

• No loss of nutrition 
• Retains freshness, texture, and flavour 
• Avoids microbial contamination 
• Avoids respiration
• Extends shelf-life  

Current Status of Freezing in India 

The Indian Frozen Food Market stood at $1204.30 million in 2021 and is expected to grow with a CAGR of 8.00% to hit $1841.28 million by 2027. Growth in the e-commerce segment, increased demand for convenience food and processed food items, and changing lifestyles are some of the factors fueling the expansion of the Indian frozen food market.

Freezing Process: How Does It Work 

During the freezing process, the product cools down below its freezing point but does not freeze. This phenomenon is known as supercooling. The product to be frozen is first cooled down to the temperature at which nucleation begins. Before the formation of ice, a nucleus (seed) is required upon which the crystals grow and this process is known as nucleation. Once the first crystal appears, the phase change takes place from liquid to solid to further increase crystal growth. 

Image source: FAO

The freezing point is the temperature at which the first ice crystal appears and the liquid is in equilibrium with the solid. For instance, the freezing point of pure water is 0°C (273°K) but when food products are frozen, the process gets complex due to the presence of bound and free water. 

Usually, the freezing process is divided into two categories. 

• Slow freezing: In this process, the thermal arrest time is more than 30 minutes. The crystals formed are larger in size which can damage the cell membrane and, hence, the cell. 
• Quick freezing: In quick freezing, the thermal arrest time is less than 30 minutes. The crystals formed are smaller in size and higher in number, evenly distributed within the cell. Additionally, since this process is comparatively quicker, no concentration effect happens and the original shape of the product is retained. 

Here is a quick glance at what the freezing process of fruits and vegetables looks like. 

Image source: FAO

Types of Freezing Methods 

Before we dive into different types of freezing methods, let us determine the factors on which the choice of freezing method depends. 

• Product dimension
• Shape
• Specific heat
• Thickness of pieces
• Freezing rate
• Packaging
• Food product components

Freezing Methods 

Here are different types of freezing methods.

Air Feezing 

One of the oldest methods of freezing, air freezing uses cool air with temperatures between -18 and -40°C. Commercially, there are three types of air freezing.

• Tunnel freezing
• Fluidised bed freezing
• Air blast freezing 

Air blast freezers recirculate cool air over foods between -30°C and -50°C at a velocity of 1.5 to 6 m/s. The airflow can be perpendicular or parallel to the food to ensure it flowers evenly all over the food products. 

Pros

• More rapid and efficient heat transfer 
• Short freezing time means reduced loss of moisture
• Reduced product dehydration 
• Less frequent requirement for frosting 

Cons

• Costly
• May result in excessive drying 

Plate freezing

In this method, packaged items or fresh commodities are put on the surface of a plate that is cooled by a refrigerant in cylindrical scraped-surface heat exchange. Usually, double plates are used in retail storage. 

Pros

• High freezing rate even for packaged products
• Less total heat load and energy use than air freezing
• Less frequent requirement for defrosting the plates 

Cons

• High capital cost 
• Limitations on the type of product that can be frozen (Package must be of uniform thickness)

Liquid immersion freezing

In the liquid immersion freezing method, the product is immersed in or sprayed with a cold liquid such as glycol or brine while being conveyed through the freezer. Usually, the products are packaged to prevent any cross-contamination or contact between the liquid and the product. The liquid is refrigerated by circulation through a heat exchanger, cooling coils, or via a jacket built into the liquid tank. 

Pros 

• Can handle irregularly shaped products
• High freezing rate

Cons

• Rarely used commercially except for some meat, fish, or poultry products

Cryogenic freezing

This freezing method relies on the change of state of the refrigerants (cryogens) that absorb heat from the food being frozen. This heat provides the latent heat of sublimation or vapourisation of the cryogen which may include liquid nitrogen, solid carbon dioxide, and others. In cryogenic freezing, the cryogen is in close contact with the product and quickly removes heat from all surfaces, resulting in rapid freezing and high heat transfer coefficients. 

Pros

• Short freezing time 
• Ease of operation
• Reduced drip loss
• Reduced flavour loss and oxidative changes 
• Improvement in product texture 
• Works well for freeze-sensitive products 

Cons 

• High cost of cryogens 

Average Freezing Times of Different Freezers 

Individual Quick Freezing: Why It’s a Preferred Choice 

Individual quick freezing is a special quick freezing method in which each and every product is frozen individually, even if multiple product types are frozen in the same area. For instance, every pea or each corn kennel is individually frozen and does not lump together.

Since this freezing method is ultra-quick, it does not allow large ice crystals to form in the fruit or vegetable cells, thus, maintaining the quality and shape of the frozen product. It rapidly lowers the temperature of the food to around -30 to -40℃  or even colder.

This method relies on blast freezing and is frequently used for berries, peaches, french fries, chicken, shrimp, salmon, peas, corn, fish, etc. Tunnel freezers and belt freezers are generally used for IQF of products. Additionally, it has low operational costs when compared to other liquid nitrogen freezers. 

Benefits of IQF Over Traditional Freezing Methods

Some exclusive benefits of the individual quick freezing method. 

• Faster:  The shorter freezing time prevents the formation of large ice crystals inside the cells. In fact, ice crystals that are formed due to slower methods of freezing are larger in size and can do cellular damage, affecting the texture, flavour and quality of the products. 
• Efficient: IQF delivers maximum uptime, meets or exceeds your hygiene needs, and makes processing easier and power efficient.
• Avoids wastage: Since each product is frozen individually and items do not cohere, consumers can take out the portion conveniently that needs to be frozen. This means no leftovers and food wastage.
• Reduces packaging: In many cases, producers package pieces separately to avoid clumping or sticking together. It is not only time-consuming and costly but also an environmental hazard. Individually quick frozen products on the other hand can be packaged together.

Final Words 

The choice of freezing method depends on various factors including product type and size, freezing rate, specific heat, and many more. However, when compared to traditional freezing methods, individual quick freezing or IQF has emerged as a preferred choice in the food industry due to its short freezing time, quality output, and affordability. 

Rinac, a market leader in cold chain processes offers straight (tunnel) and spiral belt IQF and each unit comes with a matching refrigeration package. To know more about technical specifications, get in touch with us today!