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Innovative techniques for refrigeration of dairy products & ice creams
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Monday, 31 May, 2021, 12 : 00 PM [IST]
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Prerna Puri
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For dairy plants, refrigeration is a highly essential utility required for storage of different food and dairy products at low temperature. It is also important for the cold chain of handling for perishable items like milk, cottage cheese and other food items.
In India, for industrial refrigeration, cold storages and air conditioning, ammonia-based vapour compression refrigeration system is used widely. While in dairy processing plants, ice-bank refrigeration system is used for cooling and processing of milk and for cold storages, direct expansion air chillers are used.
As far as ice cream is concerned, multi-compression and evaporator systems are being used for storing the cold dessert and other frozen products. The refrigeration system employs electrical energy for operating the compressor and other auxiliary parts of the system.
Depending on the nature of specific processing operations, refrigeration plants alone consume about 50-60% of electric power from the net electrical consumption by dairy and food plants. Hence, this makes it imperative to evaluate the performance of refrigeration plants from time-to-time and manage their operation efficiently.
As technology evolves, there are further improvements that are being made in the refrigeration techniques of dairy products and ice creams.
Importance of Refrigeration for Dairy Products
Dairy forms an indispensable part of the global food system and plays a critical role in the sustainability of rural areas, especially. Dairy industry actively contributes to the economies of many countries and a rising demand across the world is noticeably emerging currently. Thus, the industry is globalising gradually. Milk and dairy food items are essential for human nutrition and development, especially in young children.
Although being a highly nourishing food, raw fresh milk tends to rot easily by the growth of microorganisms. Therefore, its storage at cooling temperatures is imperative to preserve its freshness.
Subsequent to its collection from the farm, fresh milk is transported to cooling centres to prevent it from perishing, then to the processing units where it’s used to produce other dairy products and finally, it is delivered to the end consumers in different ways. Transporting fresh milk from farms to processing units and cooling centres is time-consuming.
As a result, cooling milk within a stipulated time becomes a major issue associated with raw fresh milk. The milk needs to be cooled down within 3-4 hours of its collection from the farm, which, if not done timely, can lead to its spoilage. Therefore, refrigeration is vital to the dairy industry.
Innovative Dairy Refrigeration Techniques
Soon after the fresh raw milk arrives at the cooling centres, it must be cooled to 4°C. This cooling process requires significant use of energy, insulated storage tanks and adequate refrigeration equipment meant for storing milk. Vapour compression refrigeration system is most commonly used for cooling milk at the centres. The basic refrigeration system comprises bulk tank, air-cooled condenser unit and a refrigeration compressor unit.
The bulk milk tanks are usually double or triple walled. The compact polyurethane foam or expanded polystyrene are commonly used for in-depth insulation which will keep the milk cool for a duration of at least 12 hours with a temperature rise of 1°C at an ambient room temperature of 30°C.
In India, ammonia-based vapour compression refrigeration systems are highly preferred for cooling in milk processing plants. The ammonia-based systems are less sophisticated low-pressure systems, with good heat-transfer properties, high efficiency and low cost.
The pungent odour of ammonia helps in the easy detection of leakage in the ammonia system. CO2 is another natural refrigerant element that is quickly becoming popular in recent times for refrigeration purposes. As against other refrigerants, CO2 has the remarkable quality of low critical temperature and higher critical pressure.
New-Age Refrigeration Techniques for Ice Cream
In the traditional freezing process, after coming out of the freezer the ice cream goes for packaging and hardening. For the purposes of hardening, the ice creams are then transferred to either plate-type conduction freezer or forced convection.
However, various advancements have been made in the refrigeration techniques being used for ice creams. Low temperature extrusion is a novel process that is widely being used. In this, frozen desserts like ice creams are subjected to higher shear stresses so as to improve the different qualities and attributes of the final frozen item. Hence, ice creams coming out of continuous freezer are then pumped into the extruder. This way, due to the shear stress, ice creams turn out to be smoother and creamier. Multiple quality changes occur in the finally obtained ice creams.
The second innovative technique being adopted for freezing and preserving ice creams is the ultra-high-pressure homogenisation of ice cream mix. This is done prior to the freezing process which reduces the size of the fat droplets in the dessert, increasing the perception of creaminess in it and stabilises the product by lowering the rate of fat agglomeration. The key factor that determines the size of the fat droplet in the ice cream emulsion is the pressure at which the ice cream mix is homogenised. This process helps turn ice creams into a lower fat, healthier product.
Pre-aeration is another innovative technique being used while preparing ice creams. Ice creams contain 60% of air volume, which is usually added in the ice cream itself. The aeration process, when performed upstream from the freezer by using a separate high-shear mixer, improved quality of the product is achieved. Pre-aeration has positive impact on the texture attributes of the final frozen product such as its firmness and stiffness. The small air cells that form on the surface lend a creamy and smooth texture to the ice cream and enhance its shape retention during distribution.
While innovations and new technologies have been slow to appear in the ice cream business, there is now enough evidence to show that such developments are essential for the evolution of the dairy and desserts industry. This has majorly to do with the rising competition within the industry as there are demands from consumers for more value and better-quality products which they consume.
(The author is CEO and founder of Prerna's Handcrafted Ice Cream)
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