Its design capability means that chickens are a stage closer to dry plucking in the way that traditional hand-plucked chickens used to be processed, leaving the skin supple and dry.
“It’s a step towards dry pluck but it’s actually dry scalding,” says Peter Kindersley, who runs the farm with his wife, Juliet.
The scalding tank
With the old system at Sheepdrove, the scalding tank is filled up with water and brought to 54C with the temperature kept continuously at this level throughout the day. The chicken [carcass] is immersed into this hot water to soften the feathers prior to the plucking process.
But the quality of the water can deteriorate, as sometimes up to 5000 chickens go through the scalding tank during the day. This, therefore, allows for faeces and bacteria build up and can lead to cross-contamination between processed chickens, he says.
Also, immersing poultry into hot water can sometimes alter the taste. Scalding tanks can melt away fat underneath the skin surface of the chicken, with water being absorbed like a sponge, producing “soggy” chicken that doesn’t refrigerate well under age, explains Mr Kindersley.
How does it work?
“A prototype was first used in a nearby barn. We learned from the prototype and from this came the hotbox, which has now been in action for more than two months,” he says.
The processing method for chicken remains virtually the same, with the birds first being placed on the line before being stunned. However, instead of entering the scald tank they are positioned inside the hotbox.
Water is heated to create steam in the hotbox and then cooled to reach 54C and this temperature is then constantly maintained. The chicken goes through a closed area and the hot humid air is blown on the bird for a period of time before plucking commences.
Reaching 54C is critical to remove the feathers. Mr Cope found that heat rather than water would lift the feathers.
The hot air box then loosens the bird’s feathers before the plucking process.
“The steam hits the chicken and this causes the moisture so the feathers then come off,” explains Ron Eyton, Sheepdrove processing manager.
“It’s been a learning curve in that free-range feathers are more embedded than those on conventional chickens, so are more difficult to remove. This is because conventional birds are younger than free range 35 versus 80 days old. Also, free-range birds are outside in all weathers.
“In addition, the jets within the box had to hit the right part of the chicken, to fluff up and loosen the feathers,” he says.
The hot air box has the added advantage of significantly reducing the risk of cross-contamination as the water remains relatively clean. This means there is less microbiological contamination of the chicken skin surface and hygiene levels are considerably improved.
Tried and tested
To assess the benefits of the new system, Sheepdrove ran the hotbox and scalding tank at the same time with the temperature and time of each carefully recorded. Samples were then taken, including microbiological samples, surface swabs from the chickens, pictures taken after the plucking process, water samples from the scald tank and water samples from the holding tank of the hotbox.
The results (see table) show that contamination on chicken from the scalding tank is higher than the birds from the hotbox.
The total viable count of water in the scalding tank reached 50 million by the end of production, while the hotbox only reached 8000. Consequently, chicken carcasses processed with the hotbox has a lower bacterial count than those processed using the old scald tank system
One benefit of having a lower bacterial count on the chicken carcass that has been through the hotbox is a longer shelf life (see graph).
On top of the microbiological benefits it is more environmentally efficient with reduced consumption of water and energy.
Water use is greatly reduced, as it uses blasts of water, compared with the scald tank that needs to be filled up every time it is used, says Mr Kindersley.
The process is run through a boiler and, as the heat is enclosed inside the hotbox, the temperature remains constant, so less energy is used. This is potentially useful with the current high fuel costs, he adds.
The hotbox at Sheepdrove currently processes 14 birds a minute and cost about £100,000. However, bespoke systems can be produced to accommodate larger processing units.