Cold Link Africa November / December 2019 | Page 29

FEATURE
INCORPORATING COLD CHAIN
Liquid nitrogen and the cold chain
By Hendrik Pretorius, Afrox application specialist for the food and beverage markets
We take a look at nitrogen and its use in modern food chilling and freezing applications.
FOOD SAFETY: NITROGEN, AN IDEAL
CLEAN GAS
By volume, dry air contains over 78%
nitrogen and nearly 21% oxygen. So, in
any cryogenic air separation unit (ASU),
the largest liquefied gas being produced
is nitrogen.
Nitrogen has no taste, colour or odour
rate, keeping the cells intact and retaining
the natural freshness, flavour, and texture of
the product.
This process is called flash freezing and
it better preserves the nutrients, taste,
and texture of the frozen food, so that
when defrosted for cooking, it is nearly
and it is non-toxic. We breathe it in and out indistinguishable from its fresh equivalent.
all the time, without any negative effects. It This technology represents a hi-tech
is also mostly inert, making it ideal for use to departure from the traditional approaches
exclude moisture and oxygen from the likes of mechanically freezing food products on
of pillow packaging for products such as a conveyor belt or immersing them directly
potato crisps. into a pool of liquid nitrogen.
Instead, with the flash-freezing process,
As a normal constituent of air, nitrogen
also has no global warming potential food on a conveyor is completely
and so there are neither pollution nor surrounded by a stream of high-velocity,
emission problems associated with venting extremely cold nitrogen vapour. Food
‘used’ nitrogen into the atmosphere. In frozen in this way is called individually quick
the context of food chilling and freezing, frozen (IQF).
therefore, nitrogen is an ideal clean gas.
Being non-corrosive also means that
potentially harmful refrigerants used in
mechanical systems.
Advantages include rapid cooling
with very stable temperature control;
reduced carbon footprint through diesel
savings; the elimination of hazardous
refrigerants (for example R404A); low-noise
design for easy deliveries at night-time
or to residential areas; longer service life
compared with mechanical solutions; and
cost-efficiencies due to ease of service
and maintenance.
Using nitrogen-based systems for food
transportation enables the food industry
to better monitor and control chilled and
frozen food’s safety and quality. It raises the
credibility of food and supermarket brands,
while protecting the environment. CLA
CLEANER COLD CHAIN
nitrogen can be used in pressurised In Europe, cold food transportation,
systems manufactured from a wide range which includes the mechanical power
of cost-effective common materials; and refrigeration necessary to keep the
the only proviso being that the material cargo chilled or frozen, is estimated to be
can withstand the process pressures and responsible for nearly 2% of total emissions.
temperature involved. Road transport refrigeration equipment,
which usually runs off a diesel-powered
FLASH FREEZING
in a wide range of operating conditions
-196°C, so on contact with an item of food, and temperatures, and it is generally much
it freezes it rapidly. Compared to freezing less energy efficient than the systems in
food using mechanical chillers, cryogenic supermarkets or cold storage warehouses.
As an alternative to relatively slow
freezing using nitrogen is up to four times
faster. This results in smaller ice crystallisation, mechanical refrigeration, total loss systems
because the water inside and outside the using liquid nitrogen are now available.
November/December 2019
truck engine, is required to operate reliably
Liquid nitrogen is at a temperature of
COLD LINK AFRICA •
Where staff might take some time to load
or offload, it is important to have a system
that can quickly establish and keep the
cold chain temperatures required. The
use of nitrogen avoids having to keep the
truck engine running while loading and
offloading produce. In doing so, instead
of diesel exhaust fumes being released
into the atmosphere around the area,
nitrogen gas is emitted, which is harmless
to the environment and to the people
loading the vehicle.
Indirect cryogenic refrigeration
systems (such as Afrox’s Frostcruise) are
purpose-designed for the food trucking
industry of today, overcoming the
environmental challenges associated
with diesel consumption and eliminating
cells of the food all freeze at the same rapid
Using nitrogen-based systems such as Afrox’s Frostcruise for food transportation enables the
food industry to better monitor and control chilled and frozen food’s safety and quality.
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