Egg cleaning during washing is related to wash water temperature, water quality characteristics (i.e., hardness, pH), detergent type and concentration, and defoamer. Chlorine or quaternary ammonium sanitizing compounds may be used as part of the replacement water, provided they are compatible with the detergent. Only potable water may be used to wash eggs and certificate to this effect is required by USDA. It is also important to ensure that the iron content of the wash water be < 2 ppm since the rate and extent of bacterial growth during storage are favored by washing eggs in water with > 2 ppm iron. The USDA suggests that water with an iron content in excess of 2 ppm should not be used unless deironized. Iron contamination may also influence microbial growth following penetration of shell membranes. As bacteria grow in an iron-rich environment, they can produce metabolic products that allow microorganisms to penetrate and diffuse into the albumen, making it a more favorable medium for growth of the microorganisms. The addition of excess iron via wash water apparently allows microorganisms to readily satisfy their iron requirements and, in turn, to grow more easily in albumen.
Regulations also require that wash water be changed every four hours or more often if needed to maintain sanitary conditions. In addition, when the difference between wash water temperature and egg temperature is > 22°C, thermal checks and cracks increase, allowing surface microbes greater access to the interior of the egg.
Contact between wash water and eggs during processing causes internal egg temperature to increase. Although blow drying following washing causes a slight decrease, internal egg temperature generally rises throughout the process and can continue to rise for up to six hours after eggs are placed in a cooler.
According to USDA regulations, eggs cannot be immersed at any time. However, eggs may be prewet to soften any adhering materials prior to washing by spraying with a continuous flow of water over the eggs in a manner that permits the water to drain away. The temperature of the spray water must be similar to that of the wash water.
Although wash water temperature must be a minimum of 32°C, most processors use wash water much hotter. A survey by Anderson et al. found North Carolina processors use wash water temperatures that range from 46° to 49°C. In 1955, Hillerman reported that wash water maintained at 46°C would increase internal egg temperature by 0.2°C/second of washing.
Alkaline cleaning formulations produce an initial pH in the wash water near 11 and wash water pH during operation is usually in the range of 10 to 11, which is unfavorable for growth of most bacteria. Alkaline pH has also been reported to increase the sensitivity of Salmonella to heat.[8,9] Kinner and Moats found that at pH 10 and 11, bacterial counts always decreased regardless of water temperature. Laird et al., however, indicated that current processing practices are not sufficient to prevent the potential contamination of washed eggs with Listeria monocytogenes.
Defoamers play an important role in egg washing. When defoamers are not dispensed properly, the foam in the wash tanks accumulates and eventually overflows from the tank. When the foam spills from the tanks, it can interfere with the water level detector, in addition to affecting water temperature and pH.
Washing, drying, and candling unit operations are generally continuous operations. Eggs detected as dirties at candling must not be soaked in water for cleaning. Soaking in water for as little as one to three minutes can facilitate microbial penetration through the egg's shell.
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