Water chilling or air chilling?

A simpler process and higher yield

Immersion chilling in a conventional counter-flow screw chiller has a number of advantages. Water is a more efficient chilling medium than air. As dwell times are much shorter, immersion chill systems take up far less space, are cheaper to buy and, if a processing plant has its own borehole, cost less to run.

Immersion chilled product also picks up water, which means higher yield for the processor. Immersion chilled birds are typically hard scalded at high temperature to remove the outer layer of skin, the epidermis. This makes for a cheaper, less critical plucking process. The scald tank is shorter and fewer pluckers are needed.

Immersion chilled product is often sold deep frozen. Where this is the case, there are no shelf life issues. Long transit times from processing plant to retail outlets are not a problem and a functioning freezer cabinet is all that is needed at retail level. Product does not have to be turned over so quickly and can remain in stock for much longer.

Water scarcity, additives and traceability

Immersion chilling has disadvantages too. Climate change is making water scarcity an ever more pressing issue in many parts of the world. Water can also be expensive. To guarantee food safety, national regulations often stipulate that chemicals be added to this water. This practice is meeting ever more resistance from consumers, who increasingly want to know where their food comes from and what is in it. In response to this, many retailers now demand that their suppliers be able to track product from farm to fork. Traditional counter-flow screw chill systems are not in line. Besides involving additional labor to re-hang, this makes the tracking of each individual product impossible.

Consumer resistance

There are other processing issues too. Water pockets can form, which can negatively influence sizing accuracy. Consumers can therefore end up with a lighter chicken than they paid for! Perhaps the biggest influence of all is consumer preference. Where “fresh” air-chilled product begins to make inroads into a market, deep-frozen products comes to be seen as somehow not being “fresh” and therefore of lower quality. Consumers begin to object to paying extra for the bloody water which comes free when they thaw their chicken out. This also leads to some questioning the hygiene of the process itself.

Adding air chilling

In markets making the transition to fresh product, a short air chill line is often installed after the counter-flow screw chiller to give a drier colder product, which is then sold “fresh” at a premium price, often in the processor’s own retail outlets. The process still involves manual re-hanging and does not permit tracking by individual product. 

Marel now offers a combined immersion/air chill system which overcomes both these issues. In this system the conventional counter-flow immersion chiller is replaced by a multi-stage water bath, through which products are transported on an overhead conveyor. After the immersion chill phase product is conveyed to an air chilling installation, often installed immediately above the multi-stage water bath. Product can now be transferred automatically both into and out of the system, saving labor and allowing product to be tracked and traced individually.

An additional benefit is the ability to manage the amount of water absorbed during the process and how the product looks. Some markets demand a white product, often with a “shiny” finish. This presentation is possible with the combined system. In addition to immersion in water during the first phase, product can also be sprayed during the air chilling phase.

Investing in equipment and space

For the processor, moving from a water-chilled process to an air chilled one involves major costly change. The counter-flow immersion chiller will have to be replaced by an air chill tunnel, in itself a large investment. As air chills less efficiently than water, dwell time in the chiller will be a lot longer and will take more energy. This means that the chilling process will take up a lot more space and could be more expensive to run. The processor will no longer be able to add as much water.

New challenges

Managing a fresh process brings other challenges too. As fresh product has a limited shelf life, accurate sales forecasts becomes essential. Otherwise, processors can find themselves with excess stock which they can either not sell at all or only at a substantial discount. Tight discipline of the cold chain from processing plant until sale to the consumer must be rigidly enforced to prevent consumer complaints and loss of reputation.

An in-line process

Air chilling tunnels can take a number of forms. They can be single or multi-tier. They can be single or multi-stage and can also be used to mature product in line. As already mentioned above, they can be combined with a short initial immersion phase. In all situations product can be re-hung automatically into the chiller from the evisceration line with chilled product re-hung automatically to a whole product distribution line. Automatic re-hang means that the chilling process can be kept in-line, saving labor and allowing each individual product to be tracked and traced through it.

The size of a chilling tunnel will depend on hourly capacity, product weight and the core temperature to which product should be chilled. This is often only a few degrees above freezing point. In multi-tier systems, the necessary evaporator/fan assemblies are often installed above the top tier. Use of the correct technology ensures that the correct volume of cooling air at the correct temperature is blown at the correct angle over and round each carcass.

Advanced moistening techniques

It is also important to ensure that product does not dry out too much, as yield will be lost unnecessarily. One example of technology developed to prevent this is DownFlow+ from Marel Poultry. A DownFlow+ tunnel has moisturizing cabinets at fixed intervals through the process. These can apply a thin film of moisture to all internal and external surfaces or to internal or external surfaces only. The number and mix of these cabinets will depend on the characteristics required for the end product. Some markets prefer a wetter product; others a drier product. Depending on the amount of moisture used, processing management will also be able to influence product color and in-pack presentation.

Maturation for top quality breast fillet

As markets develop, increasing quantities of product are cut and deboned. Breast fillet is particularly popular in North America, Europe and Oceania. This must, however, be tender and not be stringy or chewy. To avoid stringiness and chewiness, carcasses should have been matured for a period of time, a process which was traditionally done off-line. Carcasses were kept in chilled storage for a number of hours before being cut up. Marel Poultry offers a process, now widely used, which allows maturation in-line. The process uses a combination of electrical stimulation in the defeathering department and a two stage maturation chiller.

In the first short stage products are chilled rapidly by very cold air circulated at high velocity to inhibit the growth of bacteria. Moisture is applied to all inside and outside surfaces to help chilling and to keep any weight loss to a minimum. In the second much longer stage products are chilled slowly using less cold air at lower velocities. This speeds up the proteolytic breakdown necessary for maturation and a tender breast fillet.

Precise management and control

The air chilling techniques described above allow chilling and maturation to be managed in a way impossible in an immersion chill environment. Water content, color and tenderness can be precisely controlled guaranteeing the consumer a top quality, consistent end product.

No turning the clock back

Many European markets moved from water-chilled deep frozen chicken to air-chilled fresh chicken many years ago. Other markets including Canada, Australia and New Zealand follow the European example. Even in the USA, air-chilled poultry is becoming more popular.

When consumers are offered air-chilled fresh product, they invariably quote the same reasons for preferring it. Chilled fresh chicken can be presented in many attractive ways. What is attractive to the eye is tasty to the palate! Precise labeling showing an exact “use by” date, usually within a few days, indicates that product has been recently processed. Deep frozen chicken could have been produced weeks ago if not longer. In short, consumers feel that they are buying a higher quality product, for which they are prepared to pay extra.

Experience has shown that those markets, which have made the move from off-line water-chilling to in-line air chilling, have no regrets. None would want to turn the clock back!