This paper reviews the routine and periodic systems used to clean food equipment. The manner in which soil accumulates on surfaces, and factors affecting that accumulation are discussed. The mechanisms by which microbial development on the equipment surface is controlled by the system is also discussed. The contamination sequence of deposition, attachment, depletion, growth and contamination by the organism is presented in detail. Changes in surface microbial numbers over time are reviewed for system components and complete systems. The relationship between the amount of soil on the surface and microbial survival is examined. The ability of the routine and periodic systems to control soil accumulation and microbial development is discussed. Factors affecting design of a cleaning system are also presented. These factors are used to design a cleaning system, using a pipeline milking machine as an example.

A cleaning simulator was used to determine the changes in soil and bacterial numbers on stainless steel surfaces over 36 soiling and washing cycles (each of 12 h) with four cleaning systems. The soiling milk contained 106 Streptococcus faecalis colony forming units/ml. One system included a pre-milk iodophor rinse (20 C), milk soil (30 C), post-milk water rinse (20 C), alkaline detergent (50 C) and a final water rinse (20 C). The second system was similar, but without the final rinse. In the third system, the post-milk rinse was omitted. The fourth system was similar to the second, except that water at 20 C was substituted for the detergent. The simulator technique proved effective for determining changes in soil and bacterial numbers on surfaces over time. The detergent was the most important system component for controlling bacterial numbers, with the sanitizer contributing some control and the rinses very little. The numbers of S. faecalis on the surfaces were related to the amount of surface soil (detergent efficiency), and also to the inhibitory effect of solutions used before the intercycle rest period of 9.5 h between washing and the next soiling. S. faecalis did not grow during the intercycle period of 9.5 h at 30 C and a relative humidity of 80%, even on surfaces where a significant milk soil was present.

SUMMARYThe inhibitory effect of five disinfectants on acid production byStreptococcus lactisandStr. cremorisCheddar cheese starters was compared using two techniques, a laboratory scale fermentation tube test, and pilot scale cheese manufacture. Threshold inhibition concentrations (partial, total) of disinfectants (mg/1) on acid production observed in the fermentation tube were: peracetic acid/H2O2(0–5, > 600) iodophor (75–220, > 400), quaternary ammonium compound (QAC), (20–30, > 200), acidic anionic (60–120, 600–1200), and Na hypochlorite (400–1000, > 1000). Threshold inhibition concentrations (partial, total) observed in the cheese vat were (mg/I); peracetic acid/H2O2(0–5, 5–35), iodophor (15–30, 75–200), QAC (10–20, > 200), acidicanionic(30–120, > 600), and Na hypochlorite (35–400, > 400). Flavour threshold concentrations in the cheese at 4 weeks were (mg/l): peracetic acid/H2O25, iodophor 8, QAC 20, acidic anionic 12, and hypochlorite 50. It is concluded that problems in cheese manufacture are unlikely to occur with hypochlorites, iodophors, and acidic anionics, but that care should be taken when using QAC and peracetic acid as sanitizers. A correlation coefficient of 0918 was computed between the two methods of determining partial acid inhibition (P< 0·005).

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Complementary use of alkaline and acidic detergents within one system for soak cleaning was examined. A cleaning simulator was used to determine the changes in soil and bacterial numbers on stainless steel and rubber surfaces over 28 soiling and washing cycles (each of 12 h) with four cleaning systems. The soiling milk was inoculated with 5 × 105 Streptococcus faecalis and 5 × 105 Escherichia coli colony forming units/ml. In one system the soiling milk was followed by a wash with a chlorinated - alkaline detergent (20 C) and two rinses of cold water (20 C) and an intercycle period of 9.5 h. The second system was the same as the first, except an acidic detergent (20 C) was substituted for the final rinse every 9th cycle. In the third system, the same acidic detergent was used in every cycle, and in the fourth, an iodophor was used as the final solution in every cycle. The experiment demonstrated that the complementary use of alkaline and acidic detergents is ineffective in the soak-cleaning situation as acidic detergents aggravate accumulation of soil under these circumstances. Although the periodic application of a sanitizer did not influence soil accumulation, it transiently affected numbers and types of microorganisms on the surfaces. Under these conditions, the efficiency in bacterial control of the four systems was related not to the detergency, but to the performance of the sanitizer used in the system. The two substrates varied greatly in the absolute and relative amounts of soil which were deposited upon them - these differences affecting the numbers of bacteria which the surfaces supported. Neither S. faecalis nor E. coli grew during the intercycle period of any system (9.5 h, RH 90%, 30 C).