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Mussel myth an open and shut case

The habits of people choosing mealtime molluscs stick as tightly as a barnacle. Dr Karl applies some muscle power of his own to wrench open the facts.

People love their seafood. We humans have been eating mussels for thousands of years.

Now, I once believed two things about mussels. First, that you should eat them only in months that had the letter 'R' in them. And that second, you should throw away the ones that don't open when you cook them.

How easy it is to be wrong!

The first mussel myth is simple to debunk. The advice to eat mussels only in months with the letter 'R' applies only to the northern hemisphere, when the months of September through to April are when mussels are supposedly "in".

That will teach me to get my gastronomic advice from European books.

The second myth is more complicated to correct.

Look at the influential cookery books of the 1960s, such as Larousse Gastronomique in 1965 and Italian Food by Elizabeth David in 1966.

These books made absolutely no mention of discarding unopened mussels.

The myth seems to have been started by the English food writer, Jane Grigson in her 1973 publication, Fish Book.

The exact quote is:

Throw away any mussels that refuse to open.

According to Nick Ruello, the mussel expert and fisheries biologist, this advice stuck as tightly as a barnacle.

By the 1970s, some 13 per cent of cookery books were agreeing with Jane Grigson; and by the 1980s, this had risen to 31 per cent.

By the 1990s, there was almost universal agreement among the cookbook writers — none of whom were fisheries biologists.

Indeed, Nick Ruello personally contacted two prominent Australian cookbook writers and asked them why they wrote this. Their replies were that the information:

came from their young research assistants who did much of the work in preparing the latest book.

It was as though once the advice had been written down, it kept on spreading because other writers quoted it, without checking if it was correct or not.

And it was not.

Nick Ruello got involved in this mussel myth because he was commissioned to write a report for Seafood Services Australia, on the rather specific topic of adding value to mussels.

And of course, along the way, he cooked and ate over 30 batches of mussels, of various sizes, ranging from 21 to 111 mussels.

Now the mussel has a shell with two halves. Thanks to some elastic ligaments, these two halves have a natural tendency to be open.

To keep them closed, the mussel has muscles. It uses its specific adductor muscles. When we cook them, the heat can have a few effects on the adductor muscles that keep the two halves of their shells stuck together.

Sometimes, the heat can denature the proteins in the adductor muscles so that they simply disintegrate, or sometimes, it can make one or both ends of the adductor muscles come unstuck from the shell.

Nick Ruello found that 1.9 per cent of mussels opened early. These mussels opened before they had been cooked long enough to kill any potential pathogens in them.

If you removed them from the stove once they opened and ate these mussels, you would be at risk of food poisoning.

But you would get a strong hint from the texture of the meat — it would be unappetizing, jelly-like, un-coagulated, and stuck to the perimeter of the shell.

At the other extreme, he found that some 11.5 per cent of mussels remained closed after a so-called "normal" cooking time.

When he forced them open with a knife, every single one was both adequately cooked and safe to eat.

So, according to Nick Ruello, even if the adductor muscles refuse to bow to the heat, the meat is still safe to eat.

But on the occasions when he cooked them for a further 90 seconds, about one-seventh of them still remained shut.

And in the mussels that finally did open, thanks to the overcooking, the meat was now shrunken and tough.

The best way to check the safety of mussels is to check them before you cook them.

Mussels have such a small mass that if they are invaded by a pathogen or germ, they will be overwhelmed almost immediately, and will smell bad.

If we use the experimental evidence, and stop throwing out cooked mussels that stubbornly refuse to open, we can stop wasting each year some 370 tonnes of perfectly good seafood worth around $3 million.

So use a little brain muscle, and put the mussel where your mouth is.

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