Hygiene in warewashers utilizing blasting granules that foodservice establishments use.

Four kitchens, each with a different work load, were used to evaluate the microbiological risk of utilizing blasting granules in a new type of warewash machine. The granules, plastic pellets 3.5 - 3.5 mm, are recirculated together with the dishwater in the machine, and when the dishwater is expelled, the granules remain in the machine until the next day. Samples of soiled dishwater and tap water were collected on four occasions during a six-month period. In terms of CFU/ml, the APC in solutions of soiled dishwater was 2.6 ± 0.8 log, which is lower than that found in manual dishwashing (4.0 ± 1.6 log). The CFU/ml of Bacillus cereus was 2.8 ± 1.2 log and of Enterobacteriaceae was 0.2 ± 0.4 log. The microbiological levels found are representative of normal working conditions for warewash machines. These levels were compared to results obtained in model experiments, in which granules were kept, moist but drained, for 16 hours and 40 hours, comparable to standstill periods overnight or longer. On the granules in contact with dishwater for 24 or 48 hours, the APC was not increased and the level of B. cereus was decreased. There was a slight increase in the number of Enterobacteriaceae, but the model experiments did not indicate any increased microbiological risk due to the use of the granules in warewash machines. Outside the machine, cross-contamination of the faucet was indicated by the numbers of microorganisms in tap water samples.