Buying scallops, those delicious, sweet white morsels of shellfish muscle, used to be simple: you had your large "sea" scallops and your small "bay" scallops, and you could get them fresh or frozen anywhere. Now, in addition to these choices, scallop buyers need a whole new vocabulary, including "chemical free," "dry pack," and "day boat" scallops.
Lets put it simply. Dry pack means “chemical free” or “unsoaked”. For years, inexpensive frozen scallops (as well as many other frozen seafoods) have routinely been treated with phosphates, particularly sodium tripolyphosphate (STP), to reduce so-called "drip loss." STP and other related phosphates are GRAS (generally recognized as safe) food additives, and used in moderation, they help bind the natural moisture in seafood through the freezing and thawing process.
As useful as phosphates are with frozen seafood, they are subject to abuse when applied to fresh seafoods, especially scallops. If a little STP can keep the natural moisture in seafood, a lot can cause it to soak up additional water -- increasing in weight by up to 25 percent -- and since water is a lot cheaper than scallops, there is a powerful economic incentive to "soak" them.
Reports of abuse of phosphates in fresh seafood processing led to a crackdown by the Food and Drug Administration in the early 1990s, and the establishment of an upper limit on the moisture content of scallops that can be sold as natural and unadulterated. If the amount of moisture exceeds 80 percent of the weight of the scallops, presumably the maximum natural water content, they fall into a separate product category which must be labeled "scallop product -- water added."
In practice, this standard does not prevent the use of STP on fresh scallops, but it prevents processors from using STP to increase the weight of scallops without labeling them as such.