An ultrasonic washing system and its applicability in cleaning of returnable plastic crates

The hygiene of equipment surfaces plays an important role in dairy manufacture. Especially the environment in which products are packed can easily get contaminated. Returnable transport packages or crates can be one source of contamination. The cleaning of these packages is often incomplete and pathogens and spoilage organisms attached to surfaces can easily survive through the washing process. Hygiene of returnable plastic crates cleaned in washing tunnel was determined in Valio Ltd. Herajoki plant. The cleaning parameters and the microbiological quality of washing liquid were monitored. Using artificially soiled crate pieces were performed the pilot-scale studies with ultrasonic washing system. Design of Experiment (DOE, Taguchi method) was used to optimise the cleaning procedure. According to the results the bottom parts of the crates were the dirtiest parts with the worst cleaning results. Temperature, duration of washing and washing liquid quality varied much in the washing tunnel. Pilot tests showed that the sodium hydroxide (NaOH) containing EDTA was the most efficient detergent in the ultrasonic washing system. The cleaning time of 100 s and the 5 % concentration of washing liquid gave the best cleaning effects. The ultrasonic cleaning method is applicable for cleaning of returnable plastic crates and it stands comparison with the washing tunnel method.