Here s the skinny. Scallops are usually sold shucked instead of shell-on. They lose moisture readily once out of the shell. So to reduce moisture loss and increase shelf life, many scallops are treated by soaking in water mixed with sodium tripolyphosphate at the processing plant in New Bedford, Mass. or elsewhere. Treated ones are shinier, more slippery and stay more separate than untreated ones.
Untreated ones are sticky and less plump looking.
An evaluation by the Virginia Institute of Marine Science in March of 1993 concluded that consumers in their test judged the phosphated scallops to be of high quality and valued more than the non-phosphated ones. However, dry scallop fans seem to be growing in numbers. Fine restaurants feature dry scallops. A recent New York Times article by Seafood Chefs John Willoughby and Chris Schlesinger stated that the best scallops are those known as dry scallops which have not been chemically treated in any way .When cooked, wet scallops exude quite a bit of liquid which can play havoc with recipe proportions and make it difficult to brown them properly. Marcie VerPloeg, co-author of Seafood Cooking for Dummies, tells us that it s difficult to tell when the wet ones are cooked because they remain translucent instead of turning opaque the way that dry scallops do.