HYGIENIC MANUFACTURE AND PRESERVATION 731 one day and high on the next. When demineralised water has to be stored, it must be sterilized and stored in previously sterilized tanks fitted with lids capable of excluding aerial contamination. Sterilization should be carried out by boiling for 30 min, by the addition of formalin or chlorine or by ultraviolet irradiation. Care must be taken with ultraviolet sterilization to ensure that the water has a high uv transmission, for suspended matter will shield bacteria from radiation the efficiency of disinfection depends upon the intensity of the uv source, the transmission depth, and the rate of water flow. It is necessary to check by bacteriological tests that the water flow is not too fast and that adequate mixing of water is taking place by careful arrangement of the water inlet and outlet. It is preferable if water is to be stored continuously to recirculate it under a uv source. 3.5 Other sources of contamination Likely sources of contamination include sacks, bags, drums, vats, air- borne dust, straw, cardboard and the materials in which products are eventually packaged. Damp patches on ceilings and under stacks of raw materials should be rigorously avoided, as bacteria and fungi thrive in these conditions and eventually reach the manufacturing equipment and the product. Raw materials and packaging materials should be stored well away from the manufacturing area so that their flora cannot be disseminated into current production. All materials should be examined bacteriologically from time to time, preferably on a daily or batchwise basis if they carry a heavy load of micro-organisms, they should be sterilized either by ethylene oxide treatment or by autoclaving before transfer to the manufacturing area. Raw materials of mineral earth origin, including talc and pigments, may need to be sterilized before incorporation into cosmetics, to ensure the absence of tetanus spores in many instances, it may be preferable to purchase such ingredients already sterilized. Various forms of starch are also liable to be heavily contaminated. 3.6 Effect of processing conditions The operational procedures for manufacturing a cosmetic are normally determined by the need to achieve the desired product characteristics at an appropriate rate and output. Whilst it is unlikely that a process will be designed specially with the microbial status of the finished product as a prime consideration, attention to certain details may render the achieve- ment of good standards much easier than it would otherwise be. For ex-

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