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Figure 1. Build up of a bacterial biofilm on a baked bean production line. Photographs were taken using epiflourescent microscopy such that bacteria fluoresced orange while the background remained dark, (a) 4 h, (b) 8 h, (c) 12 h, (d) 16 h.

Figure 1. Build up of a bacterial biofilm on a baked bean production line. Photographs were taken using epiflourescent microscopy such that bacteria fluoresced orange while the background remained dark, (a) 4 h, (b) 8 h, (c) 12 h, (d) 16 h.

methods, physical abrasion is the most efficient in terms of energy transfer (13); for turbulent flow, a mean velocity of 1.5 m/s should be achieved (14).

Chemical energy is fundamental to both the cleaning and disinfection elements of sanitation. In cleaning, chemicals are used to break down soils so that the soils are less tenacious and to suspend them in solution to allow them to be rinsed away. In disinfection, chemicals are used to reduce the viability of microorganisms remaining on surfaces after cleaning.

Temperature or thermal energy is important for several reasons. Cleaning and disinfection chemical effects increase with temperature linearly and approximately double for every 10°C rise. Temperatures above the melting point of fatty or oily soils are used to break down and emulsify these deposits and high temperatures, particularly in CIP systems, have a disinfection effect in their own right.

Time is a factor that is often overlooked in sanitation systems. It is an essential prerequisite for the previously discussed energy forms and generally the longer the time period employed, the more efficient the process. Time can also be used to reduce the degree of energy input required from other sources when precleaning soaking is undertaken.

The combinations of these four factors varies for different cleaning systems such that if one energy source is restricted, this shortfall may be compensated for by utilizing greater inputs from the others. For example, in CIP cleaning, the energy that can be derived from mechanical energy is low but much higher temperatures and chemical concentrations are possible than can be safely used in open surface cleaning. The influence of chemical (detergents), temperature, and mechanical energy (pressure washing) has been described for open surfaces (15-18) and for CIP systems (19).

Soil removal from surfaces has been shown to basically follow first-order reaction kinetics (20,21) such that the de crease in the log of the mass of soil per unit area remaining is linear with respect to cleaning time (Fig. 2). This approximation is only valid in the central portion of the plot; it has been reported (22) that in practice, soil removal is initially faster and ultimately slower than that which a first-order reaction predicts (dotted line in Fig. 2). The reasons for this are unclear although initially, unadhered, gross soil is usually easily removed whereas ultimately, soils held within surface imperfections or otherwise shadowed from cleaning effects would be more difficult to remove.

As routine cleaning operations are therefore not 100% efficient over multiple soiling/cleaning cycles, soil deposits will accumulate on surfaces. During this phase, cleaning will become less efficient and attached microbial numbers will increase. This situation is usually controlled by the

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Cleaning time

Figure 2. Removal of soil from surfaces with cleaning time.

application of a periodic clean (23), the object of which is to periodically return the surface bound soil accumulation to an acceptable base level (Fig. 3). This is achieved by increasing cleaning time and/or energy input (eg, higher temperatures, alternative chemicals, or manual scrubbing) and is the basis of many food processors weekend clean down.

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