An emerging trend in the European and Asian feed industries involves the use of thermal heat treatment to control salmonella and other pathogens in mash feed.
Joel Worthington, sales manager, feed technology, Buhler, Inc., Minneapolis, Minnesota, U.S., discussed the new technology at the American Feed Industry Association's Expo '01 earlier this month in Indianapolis, Indiana, U.S.
Thermal heat treatment could play an increasingly important role in mash feed production, Worthington said, especially with the industry's increased focus on food and feed safety. He said the technology, which uses heat and steam to sanitize feed, is a viable alternative to pelleting or extruding, both of which require heat, time and specialized machinery.
Livestock and poultry producers that use the heat-treated mash feed have realized better feeding results, Worthington said, including lower mortality rates and better reproduction in poultry and better digestibility with less waste in swine feed.
In Japan, where people often consume raw eggs, it has been shown that hens that are fed the thermal heat-treated mash feed will lay pathogen-free eggs, Worthington noted.
"Another of the unexpected end benefits of the thermally treated mash feed is that the product undergoes some agglomeration and average particle size is increased," Worthington said. "This results in much improved fluidization properties, and a significant reduction of dust in transport and feeding."
To date, about 30 thermal heat treatment plants have been built in France, and numerous others across Europe have been built or are in the planning stages. Five such plants also have been built in Japan, including one in the city of Kashima for Kyodo Shiryo, one of Japan's largest feed producers.
The Kashima facility — which is known as the "Sunflower" plant because of the company's sunflower logo on the building's facade — is Japan's first sanitized layer mash feed plant, although four more such plants are either online or under construction, Worthington said.
The facility incorporates the latest process technology, resulting in a fully automatic, "clean" plant that produces pathogen-free feed.
The thermal heat treatment plant is a separate, independent production unit built adjacent to the existing feed mill. The plant has a line capacity of 30 tonnes per hour, and space for an additional line was left to meet future needs. The facility also is equipped with 20 finished-product silos, each with 20 tonnes capacity.
The thermal heat treatment plant for Kyodo Shiryo was equipped with a continuous production line. Worthington said other thermal mash plants are built with batch production lines, which differ significantly in plant flow and in how the mash feed is thermally treated.
PROCESS DESIGN. In the Kashima plant, raw commodities are ground to the desired micron size with dual vertical hammermills in the existing feed mill, then mixed and delivered to the thermal treatment plant by conveyor.
The thermal treatment plant is sealed and access is restricted. In addition, protective clothing must be worn when entering the plant.
Because control is automated and monitored from the main feed mill, the thermal heat treatment plant does not require operators on a continuous basis, Worthington said.
Air intake vents placed high on the side of the building bring air into the plant. Air supplied to the dryer/cooler is drawn into the facility through a filter. An ozone irradiation system sterilizes the intake air and diluted ozone is supplied to each room of the thermal plant.
Mash feed is heat-treated in a special conditioner. The mash is cooled and/or dried in a three-stage counterflow cooler. Integrated exhaust filters at the cooler and at the plant exhaust reduce cross contamination and dust emissions.
Prior to the first production run of the day, the entire process line is heated up to the processing temperature in a pre-heat cycle. Mash feed is then continuously heated and sanitized with steam in a thermal, twin-shaft conditioner. This special conditioner ensures that 100% of the mash is heat-treated at a temperature of 194° F (90° C), with a retention time of 2.5 minutes.
Worthington said that because the process uses only heat and time, without the mechanical forces applied in pelleting or extrusion, retention time needs to be somewhat longer. "There is no possibility that any insufficiently thermally treated mash is produced with this production line," he said.
The counterflow dryer/cooler with top-mounted filters dries and cools the mash in three stages without segregating the mash ingredients. The inside of the cooler consists of several compartments or levels. The top level transforms the continuous product flow into batches. When the desired fill level is reached, product discharges into the second level. The retention time of each layer can be preset.
Each segment of the production run is separate from the others, Worthington said. Each floor of the cooler opens and discharges only after the section below it has emptied.
Because it is a counterflow cooler, the cooling air is redirected to the floor above. In this way, the mash meal functions as a filter, reducing the dust in the system.
Because there are smaller amounts of mash feed in each segment, air speed in the cooler can be relatively low. Worthington said this was important because higher airspeeds would tend to entrain the mash feed particles, which are lighter than pellets or crumbles.
Various operation modes can be selected according to climatic conditions, to control the moisture content and temperature of the final product and to minimize condensation.
In a normal cooling mode, air heated to 212º F (100°C) is blown into the upper deck of the cooler to prevent condensation. The temperature of the mash exiting the cooler is normally 40° to 45º F (4° to 7°C) over ambient.
Retention time in the cooler is six minutes. As is needed seasonally, heated air also can be added in the middle deck, turning the cooler into a combination cooler/dryer.
The system can be cleaned automatically using purified air to remove any product residue. The cooler decks are thoroughly flushed by compressed air.
The plant should be sterilized about once a week, and dried out by air temperatures at about 250º F (121°C). "This minimizes the risk of recontamination of the system when the plant is not in operation," Worthington said.
The process is monitored and controlled by a computer located in the central control room of the main feed plant.
The thermal heat treatment line uses an average of 3.7 kilowatts per tonne, Worthington said, compared with a typical pelleting line, which averages about 19 kWh per tonne.
The two bulk loading stations under the finished product silos can be closed off by means of automatic roller-shutter doors when no trucks are loading. The thermally treated layer mash feed is distributed in trucks used only for this particular plant.
Kyodo Shiryo sold 100,000 tonnes of layer mash feed last year, all processed in the new thermal facility. The Japanese company hopes to reach annual sales of more than 600,000 tonnes of layer feed, Worthington said.