When start-up poultry processors first move from a batch to an in-line process based on overhead conveyor systems, the first two process steps always automated are scalding and plucking. Getting this defeathering process right is crucial for both product quality and for overall production efficiency.
Scalding and plucking are critical for visual quality and good product presentation. A suitable process will depend on local market conditions and preferences. Is there a preference for a specific skin color, white or yellow? Is product to be sold locally, often in outlets owned by the processor and under his control, or distributed further afield?
The scald process is all about subjecting the feather follicles to heat, which causes them to relax allowing feathers to be removed easily. Heat can result in removal of the epidermis, the upper skin layer. As hot water is the most effective conductor of heat, traditional scalding systems have always used this medium. Two aspects of the scald process are critical for product quality: temperature control and agitation.
Temperatures must be maintained at the required level. Too low a temperature will mean that feathers and some parts of the epidermis remain on the carcass. Too high a temperature will “cook” the breast meat, a potentially significant quality issue for processors for whom breast fillet is a high value item.
Inaccurate temperature control is an even bigger problem if birds are to be sold air-chilled fresh. Too high a temperature will result in partial or complete removal of the epidermis. This gives rise to unsightly brown patches or “barking”. In the worst case, the products could be unsaleable.
Marel heats the water in its scalding systems either by injecting steam directly into the water or indirectly by circulating hot water through radiators mounted in the scald tank.
Good agitation of hot water is vital for ensuring efficient heat transfer to feather follicles. It is important for maintaining an even water temperature throughout the scalder. The nozzles in Marel scalding systems produce large bubbles, which are aimed at the back of the product which is more difficult to pluck. Products pass through alternating rising and falling columns of water, which move feathers first one way then the other, allowing heat to penetrate deep into the follicles. Marel’s air agitation gives the best and most consistent scalding results in the shortest possible dwell time.
Ready for plucking
Once scalded, products are now ready to be plucked. Mechanical plucking machines have been around for well over half a century. While they have been refined over the years, their principle has remained the same, electrically or hydraulically driven counter-rotating discs holding rubber plucking fingers.
The number and type of plucking machines needed in a given situation will depend on hourly throughput and scald temperature. For capacities of up to 4,000 products per hour a single plucker will often be all that is needed.
Feathers from hard scalded products are easier to remove than those from soft scalded products. Skin quality will also have to be taken into account if products are to be sold fresh, particularly so if most products are to be sold whole.
A plucking line will usually consist of “attack” and “finishing” pluckers. An “attack” plucker removes most of the feathers; a “finishing” plucker removes feathers left behind. These are typically to be found on the wings, the tail and on the back between the shoulders.
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