6 questions about controlled atmosphere stunning

Vastly improved animal well-being is the main advantage of CAS

CAS Smoothflow Blue

Controlled atmosphere stunning in broiler processing has many advantages in terms of production efficiency, yield, product quality and animal well-being. Still, there might be some questions concerning CAS anesthetization, particularly about the implementation, the costs and more.

1. Why should processing plants change to CAS?

Much improved animal well-being is the main reason for moving from electrical to controlled atmosphere stunning. With controlled atmosphere stunning (CAS), operators no longer have to shackle fully conscious broilers upside-down. When shackled, birds are limp and unconscious.

Animal well-being is becoming an increasingly important issue in the poultry industry. This is particularly so in plants supplying the major QSR chains, who want their customers to know that the welfare standards for birds used to manufacture their products are of the highest order. CAS is by far the most welfare-friendly way of anesthetizing birds. While sitting in a dark quiet environment, they calmly lapse into unconsciousness without any stress.

CAS has other advantages too. Operators no longer have to deal with struggling flapping birds. They can comfortably shackle more birds per hour, which they can also do more accurately. There is scope for eliminating damage to birds during shackling. CAS reduces the risk of damage to connective tissue and blood vessels still further, as the technology does not involve passing an electrical current through the bird. CAS stuns all broilers uniformly and irreversibly.


2. What is the expected ROI when changing from electrical to CAS stunning?

A controlled atmosphere stunning system is more expensive than an electrical stunner and costs more to run. It also has a larger footprint, which will involve relaying out the live bird handling area, a major installation exercise.
Vastly improved animal well-being, the main advantage of CAS, is difficult to quantify. It will certainly burnish a processor’s image and is increasingly likely to be a condition for obtaining business from some QSR chains.
Concrete returns on investment will come from reduced downgrades, as damage to product during stunning and hanging will be considerably less. Yield and quality will both benefit.
As limp, unconscious birds are much easier to shackle, fewer operators will be necessary. Their working conditions will improve, making their recruitment more straightforward.

3. How has the CAS process changed over the years?

In 2021, Marel celebrated the 25th anniversary of its controlled atmosphere stunning system, having installed its first CAS system in a Belgian plant at the end of 1996.
The first system had two phases. A mixture of CO2 and oxygen anesthetized birds in the first phase; a higher concentration of CO2 stunned them irreversibly in the second phase. When broilers left the system, their hearts were still beating, although they could not recover consciousness. At the time, the use of CO2 and oxygen in a two-phase tunnel in high-volume processing plants was a definite world first.
Some years ago, Marel launched its ATLAS live bird handling system and its CAS SmoothFlow controlled atmosphere stunning system. Both developments were the result of Marel’s many years’ experience handling live birds and using controlled atmosphere to anesthetize them.

With ATLAS, live birds stay in their trays, which are then conveyed in a straight line through the SmoothFlow CAS tunnel. Operators shackle irreversibly stunned birds direct from the trays to the killing line.
Research and development have in time progressed to a smoother anesthetization process, resulting in even better animal welfare. As a consequence, CAS SmoothFlow now has five stages, separated by curtains, where the CO2 content of each stage gradually increases. A decreasing percentage of oxygen is part of the stunning air mix in the first stages.
ATLAS and CAS SmoothFlow are mechanically straightforward. The destacked SmartStack trays follow their way seamlessly through the CAS SmoothFlow chambers. It is an in-line tunnel system with a single conveyor running through it on one level only.
Both systems will handle 15,000 bph and more, giving proof of their superb reliability in high-volume, multi-shift plants in many countries.

Controlled Atmosphere CAS Smoothflow

4. What differentiates Marel CAS solutions?

Marel (Stork) was the first company to launch a CO2/O2 CAS system back in 1996. The only other competitor in the market used an inert gas. Inert gases are more expensive and more difficult to handle than CO2. Today, practically all equipment suppliers offer a mix based on CO2. Marel was also the first company to use oxygen. Others have since followed.
With SmoothFlow, Marel has stayed with the tunnel concept right from the start. This is technically straightforward, particularly important in high volume multi-shift plants, and guarantees the same pass time for all broilers, ensuring that stunning is uniform for all.
Marel has unrivaled experience going back 30 years of CO2/O2 controlled atmosphere stunning in many different production environments.

A CAS system in a poultry processing plant will be ‘a license to produce’

Tim Van Schaik 2019

Tim van Schaik
Marel Poultry Product Manager

5. What are the current trends in CAS?

More and more processors around the world are converting to CAS. Major poultry groups in Europe and America have committed themselves to moving all their plants to controlled atmosphere stunning. Independent poultry processors are following this trend and have made a definitive switch to CAS as well. Tim van Schaik, product manager at Marel Poultry, says, “We definitely have seen a shift in animal well-being priorities over the last few years, particularly within the context of foodservice brands and premium products such as organic or antibiotic-free chickens. This shift can be attributed to the growing awareness among consumers, and of course NGOs, to consider animal well-being when making purchasing decisions.”

Besides still further improving animal well-being, the main CAS trends are optimizing end-product quality and yields at ever higher hourly throughputs. Systems must be operator-friendly and super-reliable. Cost of ownership should be as low as possible.

CAS Smoothflow

6. How will CAS evolve in the future?

Animal well-being is becoming an ever more important topic. Electrical stunning involves the preceding shackling of live birds upside down, which is not a humane treatment. Bird stress will become increasingly unacceptable to all parties involved, from authorities to food processors, from vendors to end-consumers. On the contrary, CAS technology will continue to evolve towards further enhancing animal well-being. New advancements in CAS technology will also prioritize labor savings and a decreased number of downgrades. They will focus too on delivering the optimal air mixture to each individual broiler throughout the anesthesia process.
Tim van Schaik concludes, “The installation of a CAS system will be ‘a license to produce’ in an increasing number of situations and with an increasing number of retail and fast food customers.”


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