No matter how committed you are to home cooking, everyone eats canned foods every now and then. But sometimes you get more than you bargained for.
In 2011, a Seattle woman found what she thought were “tiny, sharp pieces of glass stuck inside the layers of canned tuna.” This was just the first complaint of glass found in canned tuna and there have been several others since then. Although they look and feel like glass, the shards turned out to be struvite, crystals chemically known as magnesium ammonium phosphate hexahydrate.
Struvite is in fact a crystal formation made of magnesium, ammonium and phosphate – mineral elements that naturally occur in fish. The separate elements sometimes bond during the canning process to form crystals. And being crystal in form, they are easily mistaken for glass or plastic, although they are more similar to salt crystals.
However, health experts confirm that struvite crystals pose no danger. The FDA says it happens from time to time. “The crystals occur naturally and therefore are not viewed as a food additives,” FDA spokesperson Lauren Kotwicki said, adding that they “easily break into pieces and dissolve during the process of digestion.”
The Seafood Products Association also confirms the FDA statement. Plus, they say that most canned seafood is struvite-free. So, in case you find the crystals in canned fish – including tuna, salmon, shrimp and crab you should simply discard them.
Local outlet KOMO News, which covered the story as part of its Problem Solvers series, suggests a simple test for telling glass from struvite:
– Pour some vinegar in a microwave-safe bowl or measuring cup. You don’t need much, just enough to cover the shards in question.
– Pop the bowl in the microwave long enough to get the vinegar warm – about 30 seconds.
– Then place the shards in the warm vinegar. After about ten minutes or so, you’ll see that most of the crystals are gone – dissolved in the acidic vinegar, just like they do in your stomach.