To provide a more appealing product for live markets, a small number of producers have adopted the practice of purging crawfish before selling them. This process cleans the exoskeleton of mud and debris and eliminates or reduces digesta in the intestine, which consumers may find unappealing. Purging requires that crawfish be confined in water or in very humid environments where food is withheld for24 to 48 hours. Purging should not be confused with the practice of immersing crawfish in salt water just before boiling, which does not evacuate the gut and is little more than an external wash.
For purging, crawfish are commonly held within specially constructed boxes or baskets that are usually suspended in water in raceways or tanks. The recommended loading rate is about 1.5 pounds of crawfish per square foot of submerged surface area with adequate aeration and water exchange. Equally effective, but seldom used, is a water spray system in which crawfish are held in shallow pools of water (0.5 inch deep) under a constant spray or mist. Holding crawfish in aerated vats or purging systems under crowded conditions for more than 24 to 48 hours is not recommended because mortality may be high. Recent research has shown that purging for only 12 hours can be nearly as effective and results in lower mortality. Though purging increases the cost of the product by 15 to 25 percent (largely because of mortality), consumers prefer purged crawfish, particularly outside of traditional markets.
Even those who are accustomed to nonpurged crawfish and do not find them objectionable might prefer purged product if the cost were reasonable. Although the current market for purged crawfish is small, purging has contributed to repeat sales and consumer loyalty to certain producers or distributors. The external surfaces of crawfish, which can be fouled and/or stained, are cleaned reasonably well during purging as the crowded crawfish rub against one another. Nonpurged animals that are excessively stained are sometimes cleaned with food-service chemicals (ascorbic or citric acid and baking soda) to enhance their appearance and increase their marketability.