A Comparison of Hand and Machine Dishwashing from a Hygienic Standpoint

In Europe, the majority of dishwashing is done manually, whereas dishwashing machines are used in approximately onefourth of washing procedures. In this work, we investigated the survival of Enterococcus faecium with machine dishwashing and hand dishwashing. Bacterial counts in the wash tank of the dishwasher were reduced by more than 3 log units within 5 minutes. Bacterial reduction was much slower during hand dishwashing, in which a reduction of 0.7 log units was observed after 43 minutes. It was also observed that the type of soil has little influence on the survival of E. faecium in dishwater during hand dishwashing.

The mean numbers of E. faecium on cleaned dishware was 13–26 times higher for items cleaned by hand dishwashing than for those cleaned by machine dishwashing. Plates that were not visually clean after hand dishwashing had higher numbers of surviving E. faecium than plates that were visually clean.

From a hygienic point of view, machine dishwashing is superior to hand dishwashing. In the machine, a higher temperature and pH are combined with lower COD (chemical oxygen demand) and faster drying, creating a harsh environment for microorganisms. Machine dishwashing is also more easily replicated than hand dishwashing, since it is controlled by the specifications of the machine.