A large percentage of the scallops available in this country have been soaked in a solution containing sodium tripolyphosphate (STPP), which causes the scallops to absorb and retain moisture, before being frozen for sale.
For this reason, scallops containing STPP are known in the industry as “wet” while those without additives (and the extra water weight) are marketed as “dry.”
To find out exactly what STPP does to scallops, we decided to purchase dry scallops and treat them with STPP ourselves. Following commercial protocols for STPP treatment, we'd be able to track how much moisture they absorbed and how their texture and flavor changed.
And by comparing them to both frozen and fresh scallops, we hoped to figure out which type is best.
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- We soaked 24 fresh (never frozen) dry sea scallops in solutions containing increasing concentrations of STPP.
- We tested 1, 2, 3, 4, 5, 6, 7, and 8 percent solutions of STPP (each also with 1 percent table salt).
- The soaked scallops were drained, patted dry, sealed in airtight bags, and frozen for two weeks.
- After thawing them in the refrigerator, we patted them dry, sealed them in bags, and cooked them to 130 degrees in a temperature-controlled water bath.
- We tasted the treated scallops next to two controls: unsoaked scallops that had been frozen, thawed, and cooked; and unsoaked scallops that were just cooked.
- We repeatedly weighed the scallops to determine moisture gain and loss.
We found very similar results among samples treated with between 2 and 8 percent STPP, and therefore averaged the results from those samples.
The scallops soaked in the STPP solutions picked up an average of 14 percent moisture before freezing and cooking. These scallops lost considerable moisture during thawing and cooking, but started with enough additional water that they ended with a net gain of 1.9 percent.
During cooking, the scallops that were frozen without treatment and those that were never frozen lost 4.2 and 5.3 percent moisture, respectively. The scallops treated with STPP lost 6.7 percent moisture, and were very hard to sear because there was so much liquid in the pan.
Tasters showed a clear and strong preference for scallops without STPP. At the low end of the STPP range, tasters noted a “soapy” off-flavor; anything above 2 to 3 percent was described as “bitter” and “unpleasant.” The texture of the STPP scallops was “bouncy” and “unnatural.”
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We learned a few important lessons.
First, buying wet scallops means paying for a significant amount of additional water weight (14 percent in our test) at the price of scallop meat.
Second, even though the scallops treated with STPP lost moisture during both thawing and cooking, they still ended up with a net gain in moisture. This resulted in washed-out flavor and a bouncy texture. Finally, we learned why it's difficult to get a good sear on STPP scallops—they shed about 25 percent more moisture during cooking than fresh, dry scallops. The liquid releases into the skillet, dropping the temperature and preventing browning.
It's clear that whereas the producer benefits from the use of STPP, the home cook pays.
Heavy-Weight Losers: STPP Scallops
We compared the weight of scallops frozen without treatment, and soaked in STPP, before we froze and after we cooked them.