732 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ample, a hot process is likely to yield a product with a lower microbial count than a cold process. When ingredients are not metered into the product within closed equip- ment, all weighing and measuring should be carried out in clean vessels, and materials should be exposed to the atmosphere for the shortest possible time. Dipsticks and stirring paddles should be fabricated in stainless steel, certainly not in timber, and should only be wiped with clean material, frequently replaced. All vessels such as mixers, storage vats, and transit containers should have well fitting lids and it is important to ensure that such vessels are kept closed, except when operations necessitate the tem- porary removal of lids. The practice of returning product from earlier batches to current pro- duction, whatever the reason, is potentially hazardous from the micro- biological standpoint. For example, "catch-pots" used on vacuum-operated liquid filling-lines to hold the overflow of product are liable to contain exposed, stagnant material unless a careful watch is kept, involving a strictly enforced routine. Clarification stages in the production process should be scrutinized for risks of introducing contamination. When a filter-press with replaceable mats is used, the whole assembly including the mats should be subject to the plant sterilization procedure. The re-use of the same mats from batch to batch obviously creates the possibility of developing a serious reservoir of contamination, unless the mats are sterilized again before each batch is filtered. Similar considerations apply to other filtration systems. The packaging operation can easily lead to microbial contamination even though the product will usually include a preservative by the time it is ready for filling into packs, it is obviously desirable to limit subsequent contamination as much as possible. Filling machines with multiple product outlets are often difficult to sterilize and the contact parts may need to be dismantled at frequent intervals for steam or chemical sterilization. Hoppers should have well-fitting lids, kept in place whenever possible. Transit from the filling stage to the point where closures are applied should be rapid if conveyors are necessary, these should be shielded or irradiated by means of suitable uv lamps. Packaging components are, in many instances, sterile at the time of manufacture but they may well become highly contaminated before use through transport and storage in unfavourable conditions, e.g. in contact with straw. Cleaning and washing procedures should be monitored with the

HYGIENIC MANUFACTURE AND PRESERVATION 733 aid of microbiological tests, to ensure that their hygienic objective is duly achieved. Although aseptic technique is seldom necessary for cosmetic manu- facture, one of the most important criteria is to avoid a cumulative increase of contamination in the plant from day to day. Detailed consideration is therefore given in the following sections to plant cleaning and sterilization. 3.7 Plant cleaning Continuous production rarely takes place in any piece of equipment and interruptions in the use of machinery may vary from hours to weeks the plant may, perhaps, be cleaned after production of the last batch of one product or just before the manufacture of the next. The idle time of the equipment is of great importance from the microbiological point of view, whether it occurs before or after the cleaning process. Undisturbed residues in damp, dark and warm regions of a plant are dangerous because the conditions are so admirably suited to the multiplication of bacteria and fungi. In pumps, joints, pipelines, pressure gauges and valves, growth is quickly initiated where small amounts of liquid are left undisturbed for a few hours. Complete and thorough removal of product residues is essential for the plant to remain in a hygienic condition. Films of product trap and protect micro-organisms and diluted material often allows the rapid development of massive numbers of contaminants. Hot detergent solutions should be used for cleaning, coupled with circulation of the solution, scrubbing and the dismantling of all valves, taps and joints. Plant should be washed, sterilized and rinsed immediately before use and if operations are to be interrupted at some stage during this process, the safest point is after chemical sterilization and before rinsing. Leaving the plant idle after detergent washing or final rinsing is potentially hazard- ous from the microbiological point of view unless the machinery is thorough- ly dried inside and out. 3.8 Plant sterilization Cleaning and removal of product residues should be followed by sterilization, especially if the plant is not to be used immediately. Steri- lization by heat is the most effective means of ensuring the destruction of all micro-organisms, but is not always convenient for manufacturing plants of moderate or large size unless special provision has been made in the