Effectiveness of a Saltwater Bath in Purging Crawfish

Linda Benedict  |  3/6/2014 1:52:14 AM

Figure 1. Notice the location of the hindgut in cooked crawfish after removal of part of the exoskeleton with the purged specimen on the left and the full “vein” of a nonpurged specimen on the right. (Photo by W. Ray McClain)

Figure 4. Dry hindgut content of crawfish from each of the four treatments expressed as a percentage of whole wet crawfish weight and dry abdominal weight.

Figure 2. There is no evidence that suggests the use of salt in cleansing crawfish is beneficial. (Photo by W. Ray McClain)

Figure 3. Flushing of hindgut to extract contents. (Photo by W. Ray McClain)

W. Ray McClain, John J. Sonnier and Anna McClain

Crawfish have been consumed in the southern United States for centuries, first by Native Americans, who later introduced the European settlers to this bountiful food resource. Immigrants who settled near the waterways and swamps of Louisiana found a ready supply, and soon crawfish became an object of commerce, dating back to at least the late 1800s. As demand increased, particularly in the larger cities, and because the wild supply varied considerably from year to year, farmers began experimenting with methods to ensure a more consistent supply. Rice farmers of the early 1900s noticed that populations of crawfish naturally inhabited their fields during the flooded stage of production. Therefore, they began to experiment with harvesting techniques and water management practices to capitalize on the increased demand for crawfish. By the late 1960s and early 1970s, crawfish aquaculture as we know it today was well underway. Today, Louisiana farmers produce almost 100 million pounds annually, worth approximately $150 million. Another $5 to $20 million is generated from the wild crawfish fishery.


Though seldom employed, commercial depuration, or purging, confines freshly harvested crawfish in water for one or two days without food prior to further sales. This process is effective at reducing the volume of material in the hindgut – that portion of the gastrointestinal tract exposed upon removing the exoskeleton from the abdomen (Figure 1). Yet, the practice of commercial depuration is not widely used in the high volume crawfish industry in Louisiana because of time and cost.


Therefore, this study was designed to obtain more definitive data regarding the effectiveness of the common saltwater bath in cleansing the hindgut of digesta. Freshly harvested red swamp crawfish were subjected to four treatments that simulated different preparation methods for cooking: (1) no washing (controls), (2) crawfish washed in a saltwater bath, (3) crawfish washed in fresh water without the addition of salt, and (4) crawfish subjected to a commercial purging process for 24 hours.


Hindgut content was collected by dissecting the crawfish and flushing the intestine with distilled water over a pre-weighed aluminum pan (Figure 3). Abdominal muscle (tail meat) was then extracted. Gut contents and abdominal muscle were pooled by sex and maturity, and dry weight was recorded after drying overnight at 167 degrees Fahrenheit. Because individual crawfish size varied, dry hindgut content weight was computed as a percent of whole wet crawfish weight and dry abdominal muscle weight.



To address the question posed by some regarding the effect of salt in a water bath on crawfish mortality, death was assessed immediately after the bath and then again after 72 hours under refrigerated storage. Less than 1 percent of dead crawfish were observed immediately after the water bath, and these may have been simply due to handling. While mortality was typically low after 72 hours of refrigerated storage, more deaths were observed in association with the saltwater bath (6.2 percent) than the freshwater bath (1.9 percent). This effect may be a moot point because in nearly all cases, crawfish are cleaned shortly before cooking only. The home consumer will likely not store live crawfish after cleaning, and the retail or restaurant trade, which typically receives live crawfish chilled, will likely keep the animals in a chilled condition until cleaning immediately prior to cooking.

In conclusion, preparing crawfish for cooking by immersion in a water bath, with or without salt, for a short time will often provide some degree of cleansing, although this is mainly associated with exterior surfaces and the gill cavity where debris can accumulate. The amount of digesta in cooked crawfish subjected to an adequate wash may not be discernible from nonwashed crawfish; however, washing will lessen the amount of debris shed during the cooking process. There is no evidence from this study that suggests the use of salt in cleansing crawfish was beneficial, but results do indicate that a saltwater bath may contribute to increased mortality, if washed crawfish are subjected to refrigerated storage for several days prior to cooking. Conventional commercialstyle purging for 12 hours or longer is the only known way to significantly reduce the size of the hindgut in cooked crawfish, and that method is usually not practical for consumers.

W. Ray McClain is a professor at the Rice Research Station in Crowley, La. John J. Sonnier is a research farm specialist, and Anna McClain is a retired research farm specialist, also at the Rice Station.

(This article was published in the 2014 winter issue of Louisiana Agriculture magazine.)

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