Scalding temperature and plucking pressure adjustments are essential for good results without loss of performance. Even with technological advances, the foundation of scalding and plucking remain basic in that heat and mechanical action are used to remove the feathers. Although separate steps in the processing line, adjustments in one step will inevitably impact the other.
The scalding process can be affected by several factors, the first of which is bleeding. The bleeding time directly affects the temperature required to achieve good scalding results. This is because the rigor mortis process, which causes muscle contraction, is directly related to the bleed time. A longer bleed time allows rigor mortis to advance more quickly and, as a result, makes it more difficult for heat to loosen the feathers.
The success of scalding depends on the time-temperature ratio, (i.e., a shorter immersion time equals a higher water temperature that will be required to guarantee a good plucking result). Scalding is where the biggest losses in yield typically occur, as overscalding (too high temperature for too long) is a leading problem with yield loss. Temperatures above 57° C, can cause overscalding mainly on the breast. Overscalding the breast is simply cooking the breast, and in this situation, direct yield is due to losses of collagen and melted fat while indirect loses are due to the formation of a layer of cooked meat that will prevent water absorption in the chiller.
The scalding tank must be adjusted according to the weight of the birds, line speed and skin color of the final product. There are basically two types of scalding: soft scalds, which are scalded with low temperatures and long periods; and hard scalds, which are shorter with higher temperatures. Normally, a soft scalding focuses on the production of products with yellow skin (presence of the cuticle) while hard scalds are more used for the production of white-skinned birds. Most countries prefer a product without the cuticle, thus require a slightly harder scalding.
Each processor has an ideal scalding time and temperature, but scalding below 57 °C for approximately 3 minutes is a good general rule. One option is the use of a multistage/multitank scalding system. Scalding systems can use a single tank with 2 or more temperature zones, while other systems can have 2 or even 3 tanks. The single 2-pass tank is the most commonly seen configuration. This type of tank uses a single temperature from the beginning to the end of the scalding process. However, using 2 or 3 tanks reduces the bacterial load of the scalding water and allows more precise temperature adjustments, where temperature is gradually increased to prevent yield loss. In the case of a 3-stage scald, it is often possible to work with multiple temperatures using cooler temperatures in the first tank (54°C) and ending with higher temperatures (56° C) in the last. This system can remove the entire cuticle of skin while preventing yield loss from overscalding.
With a limited scalding time, a temperature increase becomes the sole solution but, as stated earlier, typically leads to overscalding. Overscalding is a real problem because in addition to customer complaints about the product appearance, the economic losses due to yield loss can be huge. For example, overscalding can impact 1 breast fillet yield by up to 2%. Multiplying this loss by the annual production volume and then the selling price of a breast fillet will demonstrate just how big this economic impact can be.
It is also important to note that agitation increases the rate of heat transfer to the follicles, improving the effectiveness of scalding. This agitation is usually accomplished by the direct injection of air into the water in the tank, which moves the feathers around and improves the hot water contact with the skin and the follicles of the feathers.
Conrado Monteiro | Cobb-Vantress
After the scalding process, the carcasses must be picked as quickly as possible. For this reason, the path between the scalding tank exit and the first picker must be as straight and short as possible. Enclosing this portion of the line in a tunnel helps to maintain the temperature, which will make plucking easier. Additionally, to maintain temperature, use warm water in the pickers. However, the use of very hot water, above 60° C, can cause white spots on the breasts due to occasional overscalding.
The setting of the rubber fingers in the picking machine must go from a higher to a lower hardness along the picking machine continuum. Remember that in the first picker, carcasses are still protected by feathers and this allows the use of more rigid picker fingers.
Maintenance is a critical point at pickers, and they must be adjusted every flock change to target the largest bird. If they are adjusted for medium birds, the smaller birds will not be picked and the larger birds may be damaged (white fractures and broken skin).
The fingers should be assessed between flocks and the fingers that are worn, severely twisted or broken should be replaced. The rotation of the finger plates must also be adjusted if necessary. Generally, adjacent plates rotate in opposite directions and plates directly across from each other in the tunnel rotate in the same direction.
To achieve maximum yield, follow the 5% rule which states that about 5% of birds after the last picker may have some feathers that must be removed by manual pinning. Due to normal flock uniformity, it is usually not possible to make adjustments to the picker machines to remove all of the feathers from all of the carcasses without causing damage to some carcasses. Therefore, adjust pickers to the largest birds in the flock being processed.
Correct directional rotation of the picking finger plates is important to keep birds in the picking tunnel and not “push” them up or cause them to “ride over” the pickers. (Cobb-Vantress)
The scalding and picking processes require fine temperature and time adjustments as well as picking pressure. Checking and adjusting the efficiency of the processes must be done with every flock to produce the highest quality product.