Hygienic Performance of Commercial Dishwashers with Water-Change System -A nE x p er i m en t a lS t u d y Commercial dishwashers are used in community facilities such as hospitals, refectories, nursing homes or food services. In this area, kitchen and food hygiene is of great importance to ensure consumer health. The aim of this study was to verify the hygienic performance of commercial dishwashers with a water-change system by use of bioindicators. This test method is described in DIN SPEC 10534. Micrococcus luteus was used as the test germ instead of Enterococcus faecium as it imposes no pathogenic risk. Micrococcus luteus was identified in initial studies as an appropriate test germ for hygiene studies. Cleaning and rinsing temperatures and holding time of the cleaning program were varied. High rinsing temperature with a constant cleaning temperature and high cleaning temperatures with a constant rinsing temperature led to a reduction of the viable cell count. Increasing the cleaning temperature resulted in a higher decrease of the viable cell count than increasing the rinsing temperature.

Each consumer is entitled to have hygienically clean processed dishes and cutlery. Consequently, restaurants, caterers, canteens, nursing homes, kindergartens and hospitals are very concerned to avoid infecting their customers and patients. They are afraid of the spread of diseases by inadequately washed dishes, glasses and cutlery. This study deals with the verification of the hygienic performance of commercial freshwater dishwashers with the aid of bioindicators that are contaminated with the test soil BAMS and two different strains of microorganisms: Micrococcus luteus and Enterococcus faecium. The method used is described in the working paper “WD 00429001 Commercial warewashing machines – Hygiene requirements and testing.” Tests for heat resistance are carried out to check the temperature interval of Micrococcus luteus. Thereby, it is shown that the germ examined still shows vitality at a temperature of 70°C and a holding time of ten minutes. When testing the hygienic performance of the dishwashing programs tested, it is shown that not only temperature, but also the effects of the detergent are recognizable.

The requirements for commercial dishwashers differ fundamentally from those for domestic dishwashers. For commercial dishwashers, capacity and programme duration are the main factors. Accordingly, different designs are offered for the different types of requirement. Comprehensive data on the usage behaviour of commercial dishwashers is scarcely available. Within the framework of face-to-face interviews, 200 companies in Germany and Denmark were visited to record their user behaviour. With the help of the data obtained, not only errors in the usage behaviour were found, but also indications of unnecessarily high water and energy consumption, which, inter alia, lead to increased costs for the companies. The results show that manual pre-rinsing in particular leads to increased water consumption. Furthermore, the dishwashers are only partially loaded, which leads to more wash cycles than necessary. In order to ensure the optimal utilisation and correct user behaviour of commercial dishwashers, while simultaneously reducing the impact on the environment, there is an urgent need to educate users better on how to use them correctly.

In recent years, the aspect of hygiene has become increasingly important in all areas of daily life. Especially in the areas of gastronomy, nursing homes, kindergartens and hospitals, the hygiene aspect is of particular importance. This study deals with the examination of the hygienic performance of commercial dishwashers with a water replacement system (fresh water dishwashers) using Micrococcus luteus DSM 1790 and the carrier material oat flakes as test soil. After rinsing, the soil is detached from the test items using an elution solution. Furthermore, the sump and the back and side walls of the commercial fresh water dishwasher were examined by contact plates to obtain the microbial count. This approach has been tested for functionality in a series of empirical experiments. In addition, the influence of various commercial detergents on results was examined. It was found that the newly developed method emphasizes the difference between the tested programs. Furthermore, it was found that using a program with longer holding times led to a higher germ reduction in the upper basket than in the lower basket.

The current state of knowledge about hygiene (efficacy testing) in commercial dishwashers will be collated in this review. Therefore, studies about hygiene in commercial dishwashing are summarised and existing standards, guidelines and the legislative basis described. Finally, examples of information available from the market, for example, detergents are presented. The use of bioindicators contaminated with bovine albumin, mucin, corn starch and Enterococcus faecium is widely established in studies, which was the basis for the introduction of standards. Standards prescribe minimum temperatures for cleaning and rinsing, and most of them provide microbiological testing methods. A worldwide standardized test method for hygiene in commercial dishwashers would guarantee the comparability of country-specific standards but procedures currently available would need great efforts to be unified. A definition of a specified hygiene target level on cleaned dish items would also be meaningful because a harmless level of microorganisms can be achieved with it regardless of the initial microbial count or the process used.