Cleaning of dry
J-Tec Material Handling, Lieven Gevaertstraat 11,
2950 Kapellen, Belgium (Tel.: D32 2 6 60 53 43;
Coperion GmbH, Niederbieger Str. 9, 88250
Weingarten, Germany (Tel.: +49 751 4 08 3 98; e-mail:
The food industry is constantly changing. On one hand,
customers are getting more assertive and demanding, and the
number of products on offer keeps growing. In practice, this
means that companies have to ﬁnd a way to deal with shorter
‘change-over’ times and a need for increased ﬂexibility.
On the other hand, there is a continual evolution in the
ﬁeld of legislation and microbiological requirements.
Food companies and their staff can be held responsible
(because of new legislation) for inadmissible products
that are sold to the consumer.
For these reasons, there is a tendency towards cleaning
systems that can be validated.
By this we mean a cleaning system that is veriﬁable,
automatic and operator-independent.
It is crucial to take the decision whether to opt for a wet
or dry cleaning procedure during the design phase. Experi-
ence has shown that installations that were originally meant
to be dry cleaned can cause problems (e.g. microbiological
contamination) when a wet cleaning procedure is applied.
This is often because they do not meet the requirements
of hygienic design.
It is still highly recommended to focus on the possibility
of only using dry cleaning procedures. Introducing water in
the dry material handling area is a hazard from a food
safety point of view. Wet spots in the process lines for pow-
ders might be the source of microbiological proliferation
and the possibility of product contamination.
However, depending on the products wet cleaning can-
not always be avoided, e.g. the complete removal of aller-
gens often requires a wet cleaning protocol.
If dry cleaning is chosen during the design phase, the
installation as a whole should never be cleaned with an
aqueous solution. However, it is possible to disassemble
the components and subsequently have them wet cleaned
at a different location.
If the choice has been made to clean the installation
using both dry and wet techniques, the dryewet boundary
has to be established during the design phase. The design
also has to include the potential to effectively disconnect
the dry part from the wet part, so as to prevent droplets
or vapours from entering the dry zone.
Dry cleaning is hard to validate and a particular difﬁ-
culty lies in the fact that dry cleaning is very operator-
dependent. Most components that are dry cleaned cannot
get an EHEDG certiﬁcate based on test protocols, as
opposed to components that are used in the liquids industry.
Adequate test methods on dry cleaning procedures do not
exist (the components mentioned below are certiﬁed by
EHEDG based on wet cleaning procedures).
In general, installations designed for liquids can be
cleaned in place (CIP). However, this is not true for most
dry material handling installations. Currently, most of the
components that are used do not meet the requirements
(in terms of hygienic design) to be cleaned in place. At
present, there is little experience with cleaning in place
among the manufacturers of dry material plants.
That is why the following practice has to be kept in
mind when a powder needs to be dissolved into a liquid:
‘‘Bring the liquid to the powder and not the other way
round.’’ In this way all the powder gets dissolved. If you
bring powder to the liquid, powder residues might stay be-
hind in the dry part of the system, rendering the cleaning
The development of CIP cleaning of equipment in the
powder industry is in its infancy, but progress is being
The components shown below demonstrate that a number
of steps have already been taken to perform a wet cleaning
procedure on equipment that is used for dry materials. A)
* Corresponding author.
0924-2244/$ - see front matter Ó 2009 Published by Elsevier Ltd.
Trends in Food Science & Technology 20 (2009) S57eS59