Improved feed safety

by Stefan Hoh
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Pathogenic bacteria in feed meal are a major risk factor for animal health and performance. Thermal meal treatment significantly reduces microorganisms in feed, but requires a subsequent cooler after the hygienizing section. Difficult to clean, conventional meal coolers can be a potential source for cross- and recontamination.

Agricultural products are a natural source of microorganisms such as bacteria, yeasts and molds. The degree of contamination is subject to parameters such as type of raw material, origin, transport, storage conditions and the season. Whereas most of the microorganisms are harmless, some species, like enterobacteriaceae, show pathogenic potential, with salmonella being the most common subspecies of enterobacteriaceae in animal feed.

Infection doses for salmonella are comparatively low, with an incubation period of a few hours to two days, depending on animal species and age. Salmonella can cause serious animal disease like diarrhea, reducing feed digestibility and conversion, thus impairing animal growth and performance.

Sensitive to heat, salmonella are usually killed at temperatures above 55 degrees C. However, high concentrations of fat, protein or starch in formulated feed may form a protective colloid layer and thus increase the heat resistance of bacteria.

Hence, a hygienizing temperature of about 85 degrees C has become common practice in the feed industry to ensure that virtually all pathogenic bacteria are destroyed.

The temperature is achieved by the addition of steam into the conditioner and retained for a certain dwell time in the subsequent retentioner to guarantee a reliable decontamination process.


After the hygienizing process, the hot and moist feed has  to be cooled and dried to prevent recontamination and growth of microorganisms. This usually takes place in conventional meal coolers utilizing the principle of fluid bed cooling. Ambient air enters the cooler at the bottom side, flows through the perforation and fluidizes the meal.

Even though providing efficient cooling, meal coolers are often described as a “five star hotel” for microorganisms: The handling of hot and moist feed meal can cause condensation in the meal cooler, with free water being a major growth factor for bacteria, which resist the hygienizing process or airborne bacteria from the high air volumes applied. Furthermore, cross- and recontamination can occur due to product residues in the system, which are difficult to remove and require tremendous cleaning effort.

A new process solution utilizing thermo pneumatic conveying for drying and cooling of hygienized feed meal has been developed by the Buhler Group. The thermal meal treatment process is divided into the sub-processes of hygienizing and thermo pneumatic drying/cooling.

Hygienizing is carried out by the HYMIX and HYTHERM modules. In the HYMIX, the compound feed particles can be heated to a temperature of 80 to 90 degrees C by the addition of steam. The heated formulated feed is then retained in one or optionally two HYTHERM modules. This allows retention times between 60 and 240 seconds to be achieved as a function of the throughput rate. In addition, the HYTHERM system is characterized by its very narrow dwell time distribution, thus getting very close to the “first in – first out” principle, which ensures reliable hygienization.

In a second process step, the hygienized feed enters the Triple Air Control (TAC) system for drying and cooling. In the first stage, pre-heated air is applied for drying and cooling, utilizing the effect of evaporation. Final product temperature is achieved in the subsequent two pneumatic conveying lines, utilizing ambient air for cooling.

The optimized concept of HYMIX and HYTHERM ensures low product residues and easy cleaning. Thanks to the high air velocities applied, the TAC system is self-cleaning, which prevents product deposits. Cooling by a thermo pneumatic conveyor greatly reduces the risk of cross-contamination and recontamination in comparison to conventional meal coolers. The new thermal meal treatment system has a small installation footprint. This enables the space available in existing feed production plants to be utilized in the best possible way.

The system was installed at the Amrein Futtermühle AG, Switzerland, which produces hygienized swine feed. Operation of the new facility is fully automated and is controlled exclusively from the control room. This cuts labor costs and allows just-in-time production. The new process increases the uptime of the processing lines thanks to reduced downtimes when formulations are changed in comparison with hygienizing systems consisting of pellet mills and conventional meal coolers.

The new thermal meal treatment system can be easily tailored to specific customer needs or adjusted to feed recipes for other animal species, e.g. layer and breeder feed. This is made possible by the following options: microfiltration of the air for top sanitation standards; addition of solid and liquid micro ingredients; post-mixing application for unsurpassed product homogeneity; and monitoring of the steam quality and/or of the moisture content.


The pig feed produced by the new process is characterized by its extremely low count of microorganisms such as bacteria, molds and yeast fungi. Pathogenic bacteria such as salmonella are virtually destroyed, which significantly reduces the incidence and severity of diarrhea disorders in the animals. Besides improving the animals’ health, this also enhances feed digestibility, which in turn has a positive impact on the weight increase of the animals.

The Maillard reaction occurring during the thermal treatment process creates a bundle of roast flavors, which improve the palatability of the feed. Thermally treated swine feed may thus have a positive influence on the animals’ appetite and — according to feedback Amrein received from its customers — results in outstanding feed acceptance.

Moreover, thermal meal treatment improves the water solubility of the feed. Product lumps in the feed slurry are effectively prevented, as well as deposits of high-density particles in the feed trough.

Lastly, the heat and steam treatment causes fines to agglomerate on coarser particles, which reduces dust generation and improves flowability. Choke-ups during discharge from storage bins and silos are greatly reduced compared to untreated feed meal.