New dimension in the production of hygienized feed meal

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. A new process solution has been developed by Buhler Group, Switzerland, utilizing thermopneumatic conveying for drying and cooling as a smart alternative to meal coolers.

Contaminated raw materials

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 and storage conditions and the season. Whereas most of the microorganisms are harmless for the animals' organism, 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 incubation periods between few hours only and up to two days, depending on animal species and age. Salmonella can cause serious animal disease like diarrhea, reducing feed digestibility and conversion and thus impair animal growth and performance.

Hygienizing by heat treatment

Sensitive to heat, salmonella are usually killed at temperatures above 55 °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 °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.

Recontamination after hygienizing

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 stated 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 has persist 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 can be hardly cleaned out and require tremendous cleaning effort.

Thermal meal treatment process

To overcome the contamination problems related to conventional meal coolers, a new process solution has been developed by Buhler Group. The thermal meal treatment process is divided into the sub-processes of hygienizing and thermopneumatic 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 - 90 °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 maximum 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.

Benefits of the process

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 thermopneumatic conveyor greatly reduces the risk of cross-contamination and recontamination in comparison to conventional meal coolers. Thanks to its flexible design, 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 new thermal meal treatment system can be easily tailored to specific customer needs or adjusted to feed recipes for individual animal species, e.g. swine, 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.

Top-quality feeds

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 flavours, which improve the palatability of the feed. Thermally treated swine feed may thus have a positive influence on the animals' appetite. 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 flow ability. Choke-ups during discharge from storage bins and silos are greatly reduced compared to untreated feed meal.