When cooking with shrimp it's easy to view the shell as simply an impediment to accessing the sweet, briny flesh inside. The wide availability of peeled shrimp suggests many cooks avoid dealing with it altogether. But to overlook these crustaceans' exoskeletons is to take a pass on a considerable amount of flavor. Calling for shell-on shrimp allows us to pull a range of enticing flavor compounds into a dish—but we wanted to know the ideal length of time to cook shrimp shells for the best flavor and aroma. We designed an experiment for simmering shrimp shells to determine just that.
We simmered batches of shrimp shells (each batch contained the shells from 1½ pounds of large shrimp, or 4 ounces of shells) in 1½ cups of water, covered, for 5, 10, 15, and 30 minutes. After simmering, we strained the shell broth. To eliminate the chance that any flavor concentration resulted from evaporation, we added water back into the longer-cooked samples so that all samples were the same volume. Samples were tasted warm (160 degrees) and tasters were asked to comment on the intensity of the shrimp flavor of each sample. We repeated the test three times, each time with a different set of tasters.
To our surprise, tasters almost unanimously chose the 5- and 10-minute simmered samples as “more potent,” “shrimpier,” and “more aromatic” than the 15- and 30-minute simmered samples. By analyzing the rankings from each round of testing we found an inverse relationship between cooking time and shrimp flavor intensity.
While it may seem counterintuitive that a shorter simmering time produces a more intensely flavored stock, a closer look provides a clear explanation. While some savory compounds found in shrimp shells, such as glutamic acid and the free nucleotide inosine monophosphate (IMP), are nonvolatile (they stay in the stock, rather than release into the atmosphere), our experiment shows that the compounds that we associate with shrimp flavor are highly volatile. Shrimp shells contain about 10 percent by weight polyunsaturated fatty acids that quickly oxidize during cooking into low-molecular-weight aldehydes, alcohols, and ketones. These low-molecular-weight molecules rapidly release into the air, providing a pleasant aroma during cooking, but leaving behind a bland broth. So to get the most out of your shrimp shells, remember that longer isn't better: Keep your simmering time to 5 minutes for the best shrimp flavor.
Shrimp Shells: When is their Flavor Best?
You might think that simmering shrimp shells for longer would make a more flavorful stock, but that is incorrect. The compounds associated with shrimp flavor are very volatile, so a shorter simmer is in fact better. The best time? Only 5 minutes.