Posted by: Paul | March 26, 2010

Struvite Crystals

I learned an interesting thing yesterday.

A couple of weeks ago, during the normal weekly shop I bought a tin of salmon. A few days later, when it came to opening the tin and making sandwiches for Alison’s lunch, I turned the tin out into a dish and heard a little ‘chink’ sound. Thinking it was a bone, I searched through until I found what appeared to be a one centimetre long piece of glass.

Naturally I threw the fish out straight away, after searching to see if there were any other pieces. With other stories in the news recently about baby food being recalled because of contamination by plastic, I thought I’d take it back to the store just in case they needed to do the same with this.

Customer Services at our local Tesco were very nice, very apologetic, refunded me for the salmon and made a report to head office. They said they would come back to me within 4 weeks, so I thought no more about it. Yesterday a letter arrived from their Customer Service Centre (located in Dundee for some reason), saying that in actual fact the foreign body was not glass at all, but a substance called ‘Struvite Crystals’ which ‘occurs in most tins of seafood’. Not believing this at all – the damn thing was sharp, huge, and not at all crystal-like, and I’ve never come across this before, having eaten thousands of cans of salmon and tuna – of course I googled it. Hey presto, they were correct. Apparently they are caused by a reaction between the magnesium of the canning process and the oil in the fish. Who knew? Very very rarely they coagulate into pieces which are prism-like in appearance and can be mistaken for glass, though they are ‘harmless if eaten and dissolve naturally in the stomach’. Still, I defy you to eat something that sharp!

It’s such a rare occurrence to find one large enough to see, that I almost feel like I’ve won some kind of prize. A £10 Tesco gift card certainly did no harm. Check your tins, people!

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