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05. April 2016

Hygienic grinding of foodstuffs

The safe grinding of foodstuffs is associated with a variety of specific requirements. On the one hand, this concerns the process itself, for example, with respect to explosion safety. And on the other hand, the topic of food safety must also be considered. It is especially important by means of a hygienic machine design to avoid "dead corners" where microorganisms could possibly multiply.

The last years have seen an increase in quality requirements and an increase in awareness for the topic of food safety both in the case of consumers as well as manufacturers in the foodstuffs industry. In the wake of this development, a spate of international guidelines and standards such as ISO 22000 and ISO 14159, the GMP and HACCP specifications (Good Manufacturing Practice; Hazard Analysis and Critical Control Points) as well as the European Machinery Directive 1935/2004/EC have come into being that create the legal framework. These standards concern not only the actual processing itself but also all the objects and materials which come into contact with the foodstuffs and their ingredients. And these include especially the processing machines.

As well-known as the quoted standards generally are, as demanding is their realisation in detail. This can be seen using grinding as an example: dependent on the product to be processed, the process poses special requirements in terms of process technology. The grinding process, for example, must not adversely affect the taste and should be as wear-free as possible. Over and above this, powdery organic products are explosive from a certain particle size onwards and require corresponding safety measures. Under the aspect of food safety, deposits harbour characteristic risks. Dead spots or spots that are difficult to clean, for example, are an ideal breeding ground for microorganisms such as bacteria.

Food safety brought about by hygienic design

The solution is a hygienic design of machines, components and surfaces. The European Hygienic Engineering & Design Group (EHEDG) lays down general guidelines with the aim of avoiding the build-up of dirt deposits and of making cleaning easier. The challenge to system engineers is to bring the guidelines in line with the customer requirements in such a way that the functionality of the system is not adversely affected. In concrete terms, this can mean avoiding dead spots and corners both in the system design and the actual machine construction so that no product deposits can accumulate and all relevant areas are accessed during cleaning.


Besides an EHEDG-approved design, it is also the systematic cleaning of all system components that plays a central role in guaranteeing high hygiene standards. A demand in some industries can be a semi-automatic washing-in-place (WIP) feature accomplished with integrated systems or accessories such as spray nozzles and a downstream direct drying step with hot air. The waste water that results from wet cleaning must naturally be able to drain off without residue and the welding seams must all be free from gaps and crevices. Likewise to minimise caked-on deposits, a special surface quality for product-contact parts such as welding seams may be demanded.

Case example: lactose grinding in large dairies

As a product that has a strong tendency to form deposits, lactose poses an especially high challenge for the hygienic design of grinding systems. This applies even more to large-scale systems with high outputs, as realised by HOSOKWA ALPINE, for example, for a large dairy in North Germany. The classifier mill installed there is designed for a throughput of 4.5 t/h. Because the ground end product is used both for baby food as well as for pharmaceutical products, the mill must achieve different fineness values, e.g. 75 or 150 µm. Furthermore, the product may not be heated above a certain temperature in order to meet the requirements. The entire grinding system operates in through-air mode and besides fulfilling the explosion-safety criteria, also fulfils the customer's requirement of a low fine dust emission of less than 5 mg/m³ as defined in the Technical Instructions on Air Quality Control (TA Luft).

Because of the demanded high system availability, the explosion protection and the size of the system, it was necessary to install a WIP system and to make adjustments to the design in order to meet the high customer requirements in terms of hygiene.


In the last 3 years, alone 8 grinding systems which meet the high market demands were delivered by HOSOKAWA ALPINE for lactose applications. Generally speaking, the awareness for hygiene in the food processing industry is on an all-time high and companies such as ours are being confronted with increasingly higher demands, demands which must be considered both from a customer-specific as well as from a industry-specific point of view.