HYGIENE IN MANUFACTURING PLANT AND EFFECT ON EMULSIONS 397 THE ORIGINS OF CONTAMINATION Water supplies, raw materials, sacks, bags, drums and vats in which ingredients are packed, air and dust, and the final product packing materials are all vehicles by which unusually large numbers of micro- organisms can enter even the best run factories. Unfortunately, spot- checks for microbial contamination do not provide a complete safeguard as pockets of organisms in otherwise satisfactory materials and equipment can often provide greater problems than moderate numbers evenly dis- tributed throughout. These pockets can easily be missed by the usual microbiological test techniques, and the only solution to this insidious problem is awareness of possible danger points, constant vigilance, and high standards of factory control. Demineralized water is contaminated more often than not, and the resin beds of ion exchangers are usually responsible. Baker (2) has cited a case where water entering an ion exchange unit contained four to five bacteria per m!, and left the apparatus carrying 500,000 per mi. Frequent sterili- zation of the resin beds in these units is desirable because the organic matter trapped in them provides excellent growth conditions for organisms. Eisman et a! (3) have also studied this problem and suggest that if the deionizing units are operated daily, contamination is less likely to occur than if they are only used intermittently and water is stored in large quantities where rapid multiplication can occur in short periods. Cruick- shank et al (4) found irrigation of ion exchange beds with 0.25 per cent formalin (0.1 per cent formaldehyde) satisfactory for sterilization. In factories where filtered tap water is used instead of demineralized water, the same attention should be paid to the filters as to deionizing beds. Frequent renewal of filters is, of course, preferable to sterilization particularly if organic matter collects in the filter, as this is often present in sufficient quantity to render the sterilizing fluid inactive against the organisms present. Stagnant water, and damp patches on walls, ceilings, and under stacks of raw materials are an eternal enemy to hygienic manufacture, as both bacteria and fungi will thrive in these conditions, become airborne, and eventually enter the plant. Equal, if less obvious, sources of aerial contamination are draughts which disturb dust and microbial spores. Of the raw materials entering a factory those of natural origin, such as the gums tragacanth, acacia and karaya, and solids like chalk, talc, kaolin and rice starch, are much more liable to carry large numbers of micro-organisms than the refined oils, fats and waxes, or synthetic materials,

398 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and should, where possible, be stored away from the plant and out of draughts which could disseminate their flora. PLANT CLEANING Fully continuous production of a single formulation seldom occurs in any one piece of equipment, and many cosmetic and pharmaceutical factories make several formulations in the same plant. The intervals between use of the machinery may vary from hours to weeks, and the plant may be cleaned immediately after production of the last batch of one product or just before manufacture of the next. The time during which the equipment is idle is, however, important from the microbiological point of view regardless of whether it occurs before or after the cleaning process. Undisturbed residues in dark, damp and often warm areas of a plant are danger points, because these are the conditions best suited to rapid microbial multiplication. Favourable growth conditions also occur in a plant which has been sluiced through with warm detergent solution and left without further treatment. Many types of bacteria grow actively in dilute detergent solutions and a quick rinse through of any plant will remove some, but not all, of the previous product, leaving a nutritious mixture of detergent and product in which the preservative has been diluted beyond effectiveness. Few manufacturing plants are entirely free from stagnation areas in pumps, joints, pipelines, pressure gauges and valves, and large masses of microbial growth can form in very small amounts of liquid left un- disturbed for a few hours. Sokolski et al (5) have reported an example of contamination of a product from an accumulation of organisms in a trap in a production pipeline. The product contained clay, which can often be heavily con- taminated, and pectin which can be metabolized and give rise to rapid growth. It also contained methyl phydroxybenzoate, and the product was usually perfectly satisfactorily protected against growth of the normal number of organisms present. However, when the trap in the pipeline became heavily contaminated with organisms, clumps of growth occasion- ally broke away and the numbers were sufficient to overcome the pre- servative and cause product spoilage. Another interesting observation in this case study was that the offending organism Cladosporium resinae was capable of utilizing the preservative, methyl phydroxybenzoate when its concentration was reduced below 0.15 per cent. Complete and thorough removal of product residues is essential if a