Throw Away Unopened Mussels? Who Says?

Posted on 09 Apr 2012 21:35

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Most people who like to cook and eat mussels and clams know that they are done cooking when the shells open. As you may have gathered from the title, I'm going to question that. In fact, I'm going to have the question the whole tale about how if they don't open, it proves they were dead, and so you must discard them. You see, there is just no science to it!

Before I get into this, let me give you a piece of wisdom that I learned in dealing with strength and fitness topics, and that will form the basis of what follows: It only takes one influential person to say one thing once, at the right time and place, for it to become gospel. No science needed.

Here is how your basic instructions go for mussels, which will be our example here, because I like them better than clams, they are less complicated, and you know those little membranes you have to pull off the soft shell clams do not make me happy. Plus, mussels don't generally have sand in them…I'll get to the reason for that later. However, I know of at least one cooking resource, Cooking by James Peterson, which questions the wisdom of discarding unopened steamed clams, saying:

Clams take longer to steam open than mussels, usually about 10 minutes. Invariably, a few remain closed after all the others have opened, and despite the claims of many recipes, they are usually perfectly fine. Just slip a knife tip between the two shells and the clam usually snaps open. Don't do this over the rest of the clams, however, just in case the clam is dead and full of mud, which could ruin the rest of your dinner.1

Interestingly, he does recommend cooking mussels until opened, or at least it seems he does. However he does not recommend throwing away unopened mussels but instead seems to be saying you should simply continue cooking unopened mussels until they do open. Why? And will they all open eventually? I'll get into that a bit later. Suffice it to say, for now, that throwing away unopened mussels and clams does not seem to be a foregone conclusion to all cooking experts. And James Peterson's "Cooking," by the way, is an excellent, excellent resource. If you want to learn to cook, you should have it on your shelf. So, here are those basic instructions I mentioned before:

Basic Instructions for Dealing with Mussels

1. Mussels must be bought, and stored, alive, so cook them soon after you buy them, preferably the same day.

2. When you're ready to cook them, if you find ones that are open, tap them on the counter, or with a knife, etc. If they don't close, discard them (closing proves they are alive).

3. Once you begin cooking them, they will open, because the heat kills them and relaxes the muscle that keeps them closed. This also proves they were alive, and that they are now cooked.

Should you really throw away unopened mussels and clams?
Should you really throw away unopened mussels and clams?

A Little About Bivalves

Mussels and clams are bivalves. Nothing much more than two hinged shells with a muscular mass inside them that closes the shell, and digests nutrients. There is a ligament at the hinged part of the shell, call it the rear, and this is attached in a way that basically makes it act like a spring that forces the shell open. This means that the bivalve's natural, or "default" position is open. The mussel's adductor muscle acts to overcome this ligament's tension and force the shell closed.

So, if before you cook it, the shell is open, that just means the mussel is chilling out. But once you bother it by tapping it on the counter, it should close right up. Meaning the little guy is alive and his adductor muscle is in working order. But if he doesn't close, then, that must mean that he's dead, and his adductor muscle is less than sound. Maybe it's even a bit mushy and disintegrated.

clams and mussels in broth

Clams and Mussels with Broth

clams and mussels in broth

Clams and Mussels with Broth

Now, I've actually got no problem with this part of the story. The healthy response of the healthy bivalve, upon being whacked, is to close up tight. But the part about the heat making the adductor relax, thus opening the shell, that got me to thinking, who says? The thing is, there always seems to be some unopened mussels in every batch, and I began to think that maybe I would research this a little and see where it came from. All I found was a lot of the same thing being repeated. But it makes no sense, as if the adductor "relaxing" is supposed to open the shells, well, they would probably have already been open. And if they were open, you would have whacked them a good one to see if they would close. It's a bit circular.

The Curious Case of the Missing Mussels

I went around in this circle, and then was lucky enough to happen upon a book written by Karl Kruszelnicki called Curious and Curiouser. He apparently is Australia's BEST-LOVED SCIENCE GURU! But I'd never heard of him since, of course, Bill Nye is my science guy. The book includes a section called, 'Mussels - An Open and Shut Case?'

The author starts by saying there is no mention of the myth in two influential cookbooks of the mid-1900s, Larousse Gastronomique and Italian Food by Elizabeth David (1961 and 1954, respectively). I cannot confirm this as I was unable to find an edition of the former and was only able to find a modern edition of the latter, Italian Food by David, and it did mention the shells opening but not the discard part. The author also claims that it was mentioned in Italian cookbooks as early as 1915 and possibly earlier, but in the "English Language" it seems to have been started by food writer Jane Grigson in her book Fish Cooker, published in 1973, but which is actually called Fish Book.


Mussels on a Line


Mussels on a Line

He goes on to say that by the 1970's, 13 percent of cookbooks were agreeing with Grigson, and by the 1980's, this had risen to 31 percent. Such precise figures! Apparently by the 1990's there was almost universal agreement among cookbook writers.2 I don't know how one could possibly have confirmed such statistics but I'd say that, despite the evidence of James Peterson, above, yes, most everyone agrees these days, including most chefs who do not write cookbooks.

It is clear from my research that to "cook mussels until they open" was a very common instruction well before the 1950's, at least as far back as the early 1900's. It is mentioned in several works by James Beard prior to that time, as early as 1949. It is mentioned in numerous and various documents of the early twentieth century, as well. Cooking mussels until they open, or a variation, until they begin to open, is nothing very new at all. I too, however, was unable to find any mention of throwing away any unopened mussels prior to Grigson's statement, and I have no knowledge of the "Italian cookbooks" that mention the myth. According to Kruszlnicki, Grigson gave no clear reason as to why the unopened mussels should be thrown away, so we cannot even be sure when the idea that unopened mussels were spoiled came about.

The Pearl in the Mussel Can

Now, if I could guess as to where the basic instruction came from I'd say from the canning industry, as cooking mussels and clams until they open would be economical and expedient, far better than shucking bivalves by the thousands by hand. Even freshwater mussels have been canned in the past, although we hardly touch them today. And there was the freshwater mussel pearl industry, which would have also cooked droves of mussels until opened, to get at pearls, should they exist. There may be another practical reason for the later perpetuation of it, however, that does not necessarily have to do with expediency and economics. This is also related to why James Peterson recommends cooking mussels until they open.

steamed clams in broth

Steamed Clams in Broth

steamed clams in broth

Steamed Clams in Broth

Mussel Danger!

Regardless, cooking mussels until they open is an old, old instruction. Whether Grigson got the ball rolling on discarding unopened mussels, it is near impossible to tell. Whether she just made it up or had been taught this we may never know. It certainly was not a foregone conclusion, according to the science of the time, that you could tell if a mussel was good by how it behaved when you cooked it. Mussel poisoning used to be quite a big problem. Often, mussels were gathered in areas of sewer runoff, for instance. It was quickly known that the dangerous contaminates in these mussels were not affected after a few minutes of cooking, and opened mussels would have meant nothing. In some outbreaks, boilings of 30 minutes failed to ameliorate the danger.

On the west coast of the U.S. it became apparent early on that consumption of mussels gathered in the warmer months was always dangerous. Poisonings were reported, like the one outlined in this paper from the California Dept. of Public Health, in 1929].9 Although the cause was unknown at the time, this poison outbreak was obviously due to the now well-known "red tide", a bloom of plankton called dinoflagellates which sercrete toxins that enter the mussels and cause poisonings in humans which cause, as the report mentions "motor nerve paralysis", better known as paralytic shellfish poisoning. The same types of toxin danger has happened along other coastlines and cooking has no effect on the chemicals. As the paper says, the bad mussels "can not be distinguished from sound mollusks either by appearance or behavior on cooking."

many quail eggs

Certain areas may be semi-permanently posted
off-limits for harvesting due to over-harvesting.
Other areas may be temporarily posted
due to toxin.

many quail eggs

Certain areas may be semi-permanently posted
off-limits for harvesting due to over-harvesting.
Other areas may be temporarily posted
due to toxin.

Bad mussels, in fact, were known to be a common problem in the late 1800's and early 1900's both of the paralytic or nervous toxin variety or the gastroenteric variety. Given the history of the mussel as causing either toxic or pathogenic food-poisoning outbreak that did not always respond to extended heat application, it is hard to see why anyone would assume that an open mussel should be a good mussel, as many of these poisonous mussels would have indeed opened, simply due to the fact that the adductor muscle broke down.

Now, although there is still the concessional outbreak of food poisoning from shell fish contaminated with pathogens, and, unfortunately, still illnesses from paralytic shellfish poisoning, there is very little need to worry about the kind of stubborn pathogens that were present in mussels gathered from sewage contaminated waters these days. We don't dredge wild mussels very much now, so they don't come from mud and muck. Although you can still get wild mussels most of the mussels we eat now are 'cultured.' They come from nice clear water above the sand, where they spend their time hanging out, literally, on lengths of rope. The bonus is that this is a more environmentally friendly practice, as we don't churn up and damage the sea floor by dredging it for mussels.

Enter the Fisheries Biologist from Down Under

Curious and Curiouser, which is a cool science trivia book, led me to another guy named Nick Ruello, who is the origin of the Jane Grigson connection. Ruello is a fisheries biologist and former manager for Fish Marketing at Victorian Dept of Agriculture & Rural Affairs, Australia and now chairman of Ruello & Associates3. He was commissioned to write a report for Seafood Services Australia, a nonprofit company funded by seafood industry Fisheries Research and Development Corporation, which is a cofunded partnership of the Australian government and the fishing industry. After reading his report, and the article in FRDC's June 2007 Newsletter, "Blue Mussels: an open and shut Case" by Melissa Marino with comments from Muello about his research, I think the case of the unopened mussel has been closed.4,5 Both these reports are freely available on the web, so you should read them for yourself for further enlightenment. The links are available in the resource list for this post, below.

Why would Muello, the fishing industry, and others, be interested in stamping out this myth? According to Muello, this myth causes the waste of about 370 tons of good seafood per year, worth at least $3 million. To me, that is wanton waste and I think is a very good motivation to question the validity of discarding these shellfish.

Muello's research regarded the post harvest handling of farmed blue mussels and the primary purposes of the report were to 1) Identify the key quality and marketing parameters for chilled mussels and prepare product specifications for “premium” and “standard” mussels, 2) Develop a Code Of Practice which takes account of product labelling, uniform size grading, shell fouling and cleanliness, condition index and any mandatory food safety requirements for the guidance of all industry sectors, and 3) prepare a product Trade Users Guide for wholesalers, retailers and restaurateurs.

Along the way, he also performed research to "explore the basis of the advice commonly given by cookery writers to discard mussels which do not open after cooking."

It made sense to do this since Muello and his wife, also a scientist, already had to do a huge number of trials to develop the quality grading index sought for mussels. As always happens, they were cooking the mussels to collect data on the flesh content and a few, invariably, would not open. Out of curiosity, says Muello, he opened a few and found that they were all cooked.

Consequently, Muello went ahead and did 33 formal experiments over 32 months, as his own guinea pig, testing mussels from different places and different times of the year. He also performed lots of informal trials to lend more support to his findings.

The unopened mussels, after a typical cooking time, ranged from zero to 90 percent and at least some of the mussels remained closed in 90 percent of the tests (which is my experience as well, albeit it comparatively limited). After further cooking for 90 more seconds, about 13.2 percent still remained closed. And some just never opened no matter what. Yet, says Muello:

We found the unoponend mussels to be no more dangerous than the open ones. Rather than being discarded, closed mussels should be opened with a knife to check their condition and cooked a little more if deemed necessary. These could then be regarded as safer to eat, given their greater exposure to heat.

Muello thinks that the advice to throw away unopened mussels was nothing more than a well-meaning but unfounded instruction stemming from cookbook authors and teachers repeating what they had been told, even though what they had been told was just an old-wives-tale, having never been subject to scrutiny.

Breaking It Down, or Rather, the Breaking the Adductor Down

So what does this all come down to? We already know that most dead mussels have shells that are open and that do not close when tapped. Why would a dead mussell's shell be open? Because, remember, open is the "default" position due to the spring-like tension of the ligament arrangement. The softer adductor mussel deteriorates before the more resilient ligament, and thus the shell opens.

Haven't you ever wondered why you check to see if they are alive before cooking them and then 'check' again by confirming they are opened? There never was any reason for it. Most mussels, when dead, WiLL BE OPEN. Because the addcutor breaks down and turns loose the shell. Once you've tapped and confirmed any opened mussels are alive, there is no point in any further precaution of this nature. A wild caught mussel, I suppose, may sometimes die and have it's shell fused closed by mud and muck but I've never personally encountered this.

Why do some mussels open sooner than others, when cooking? Maybe because some mussels are older than others, and therefore their muscle is weaker, which is what Phil Lamb of Spring Bay Seafood suggests in the FDRC report. The fresher mussels have fresher muscles and so they can sometimes "hang on like hell." But do you really expect the process of all these different mussells having their adductors break down to the point of tearing loose be an exact kind of thing? Certainly it is reasonable to expect that a few will take longer than others, and that there may be stragglers that just don't turn loose after any reasonable period of cooking, which for a mussel is very short.

Now, remember when I kept hinting that James Peterson had another, more practical reason for saying to cook the mussels until they were opened? The reason is simple. If you do not, some of the mussels that you open with a knife, although they will pop open easily, will not be sitting pretty on one half of the shell, but will remain clinging to both halves, and may even tear. You then have to dig at it a bit and mussels usually come right off the shell with very little effort. I suspect this is where Peterson's advice stems from. He also mentions looking for any mussels that are open but still attached to both shells and cooking further. This could only happen if the muscle tore or separated without detaching from the shell, I would think, and I would not engage in further cooking for this reason, as it would only serve to over-cook the mussels. I could be wrong, of course, as Peterson is much more of a cooking expert than I will ever be.

So, cooking mussels until they open, was probably nothing more than a practical thing to some, whereas to others, it became a proof that the mussel had been alive. It is hard to say why anyone really ever thought this "proved" a mussel was alive and fresh, but I think it was probably because they believed that a live and fresh mussel opened up as a response to heat. You get the picture, like they open up their shells to cool off or something and if they don't, well they must have been dead. Of course, this is dead wrong. The response of a mussel to any kind of threat is to close up tight.

So, you see, there just was never anything to it at all. Mussels open, most of the time, when cooked, because the muscle that holds the shell close breaks down and detaches from the shell, allowing the tension of the more resilient tendon to pull open the shell. If they don't open, it proves nothing more than that it's taking a bit longer for the muscle to detach. Now that you know, you can stop wasting mussels!

We all want to be sure that our mussels are good, of course. Well, you're going to do the tap test on any open ones. Plus, some advice from Michael Bacash, a seafood chef in Melbourne, is recounted in the report. Besides mentioning that fresh mussels will close their shells when tapped, he says checking a mussels weight and smell before cooking are the best tests you can do. The freshest mussels, besides being closed, will be full of water. He too agrees: "Whether they are open or closed on cooking is not really relevant."

James Peterson gives another test for dead mussels, which I've heard before. This one is based, again, on a healthy mussel keeping it's shell tightly closed. He says to push the shells sideways in opposite directions. Any dead mussels will open and fall apart in your hand. He seems to have missed the memo. They would have probably opened up long before, if they were so far gone as to "fall apart in your hand." But what are you gonna do? I still love the guy.

You ever seen frozen mussels? Yes, I've had some from time to time when I couldn't get any fresh. You can get them in boxes already with butter and garlic sauce, ready to drop in a pan and cook up. They're not bad. I know foodies will sneer and turn their nose up but I think they are okay in a pinch. Guess what, frozen to death mussels open further when you cook them (although they are already cooked at least partially). So, anyway…

The only problem to me, with frozen prepared mussels is that the sauce needed white wine to get that classic steam mussels taste. What's that classic steamed mussels kinda thang, you ask? Well, here is your recipe. Remember, when I say 'classic' I mean there just isn't much that can be improved, it's pretty much perfection and that is why it's a classic. You can play around with different herbs, but really what you want is some nice seasoned and grilled crusty bread to go with it. You know, to dip in the sauce.

Oh, one more thing before the recipe. You may be wondering on how many mussels you need for you and your friends. It depends of course on if you plan to eat nothing but mussels or the mussels are just an appetizer. For an appetizer you want 1/2 to 3/4lbs per person. For a main course you want at least 1.5lbs per person. I'd get more…they always go. The recipe below serves up a "main course" for 4 people.

Steamed Mussels in White Wine Sauce

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6lbs mussels, scrubbed and rinsed
1 cup dry white wine
3 shallots
1 clove finely minced garlic
3 tbs chopped fresh parsley
4 tbs butter


Put the wine, shallots, and garlic into a deep stock pot and simmer, coverd, over low heat for five minutes.

Add the mussels all at once and cover, raising the heat to high. Boil for two minutes and, using a pot holder or towel to secure the lid, shake the post to redistribute the mussels in the broth. Steam for 2 more minutes, then check to see if most of the mussels are open. Cook two minutes more, if you think it's needed. Try to keep the cooking to 4 to 6 minutes. Some sources recommend 10 minutes for safety, but this will generally result in over-cooked mussels.

Remove the mussels from the pot, and put them into a large serving bowl, or individual serving bowls, depending on how you are serving them. Leave the broth behind. Check any unopened mussels with a knife, away from the other mussels. If they are full of mud or otherwise look or smell wrong, discard them.

Check the broth that you left in the pot for grit, which will have settled to the bottom of the pan, if present. Grit is unlikely, unless your mussels were wild caught or you didn't clean them properly. If there is grit, carefully pour the liquid into a sauce pan, leaving any grit in the bottom of the pan. Add the butter to the broth and boil, stirring, until thickened a little. Pour the broth over the mussels and sprinkle with chopped parsley. Serve immediately with crusty slices of bread, preferable grilled for a smoky taste.

Some Important Tips on Storing, Cleaning, and Preparing Mussels!

  • Never buy a mussel with a chipped, split or broken shell. If you do end up with any…just toss them.
  • It's best to cook mussels, and any shellfish or fish for that matter, the day you buy them. If you cannot, however, store fresh mussels in a bowl inside the refrigerator, covered with a wet towel, for not more than one or two days.
  • Many cookbooks advise that you should immediately place your mussels in a container of cold water to store them. NEVER do this. They will quickly die and as you may have gathered, dead mussels are inedible mussels.
  • Mussels may have little beards (called byssal threads) that stick out the edge of their shell. This what they use to attach to things in the water. NEVER pull off the beard in advance as this may kill the mussel. The beards should only be removed, with your fingers, just prior to cooking. If it's hard to remove use a kitchen towel to grip it. Sometimes I use I get the beard between the blade of a small knife and my finger to pull it. This provides more grip as well. Some cookbooks instruct a special way to pull the beard out, to avoid killing the mussel:

* Instead of pulling the beard out toward the opening end of the mussel, pull towards the hinged end. This is supposed to avoid killing the mussel. I still always wait to beard my mussels until not more than 20 minutes before cooking them.

  • Despite all the goings on above about tapping mussels that are open, this instruction assumes the mussel is just slightly open. If you find a mussel that is gaping wide open…forget about it. You will probably be able to see it is bad, or smell. Chuck it..mussels aren't big mouths.
  • Check your mussels for weight. The ones that feel much lighter or much heavier may be dead. Give these a sniff and go ahead and try pushing the shells apart sideways to see if they stay together.
  • Good live fresh mussels don't smell fishy in a bad way. They should smell like a day at the beach…a clean non-polluted beach. If it makes you wrinkle your nose or feel like you're about to throw up…well…
  • Most mussels we get today, as mentioned, are cultivated. They will not likely have barnacles on them so you won't need to scrape them. I still scrub them with a brush while rinsing them..but I'm just like that.
  • Cultivated mussels rarely contain any sand. If you do get sandy mussels, you can soak them in salt water for a couple of hours, which should cause the mussels to expel the sand. One-half cup of salt per quart of water. 12

So, What's The Take Home?

The take home is that if you've read all the way to the end of this article, you are my kind of reader and I love you for it! A lot of people might read this, and think it to be quite reasonable, but still, out of a modicum of caution, choose to throw away any unopened mussels. To that, I say, I don't blame you! I personally, don't throw them away but if you think I'm trying to convince you to do as I do, think again! I've done a lot of research and used a lot of reasoning to come to my conclusion, but the honest truth is, I still can't tell you for sure. Heck, this article is as much for the curious as for the person who really wants to use the information. I like both kinds of readers!

Now, if you have gotten sick after eating mussels (or clams), and you thought it was an unopened mussel, there is one thing you might want to consider. How do you know? See, you had already been pre-influenced to believe, like most of us have been, that unopened mussels were bad, despite a lack of any real evidence to support that belief (we were told by experts!) But, if you get sick after eating a mess of mussels, all you really know is that you got sick and you have a reasonable doubt about the freshness of the mussels. Sans actual testing of the mussels, you can't even make an accurate causal inference. What you really have is a correlation, although, depending on how soon after eating the mussels you get sick, a causal inference certainly might be reasonable!

So, what you know is you got sick and you are pretty sure that it was the mussels, if not very sure. But that is all you know. You don't know it was an unopened mussel unless for some odd reason you ate one unopened mussel and no other mussels, or a bunch of unopened mussels. That is not likely. Therefore, you have no real reason for blaming the unopened mussel, out of all the other mussels, other than prior beliefs.

And yet despite this, I still don't blame you if you throw away your unopened mussels. I am not providing any guarantees that you will always be safe if you do not throw away unopened mussels. How could I? Mussels can be bad at any time. Your decisions regarding food-safety, and mussel safety, are yours and yours alone. This article is provided for information purposes and you must weigh this and any other information you may find, in order to come to your own decisions about how to prepare and cook mussels, clams, and other bivalves.

1. Peterson, James. Cooking. Berkeley, CA: Ten Speed, 2007. 110.
2. Kruszelnicki, Karl. Curious and Curiouser. Sydney: Pan Macmillan, 2010.
3. Ruello, Nick. LinkedIn profile. <>
4. Ruello, Nick. "IMPROVING POST HARVEST HANDLING TO ADD VALUE TO FARMED MUSSELS." FRDC. Seafood Services Austrailia, Jan. 2004. Web. 9 Apr. 2012. <
5. Marino, Melissa. "Blue Mussels: An Open and Shut Case." Fisheries Research and Development Corporation News: FISH 15:2 (June 2007): 4. Web. 9 Apr. 2012. <>
6. Smith, Hugh, Commissioner. "Annual Report of the Commissioner of Fisheries."
7. Rosenau, M. J., George Chandler Whipple, and Thomas W. Salmon. "Chp 3: Animal Foods: Shellfish." Preventive Medicine and Hygiene,. New York: D. Appleton and, 1917. 565-67.
8. Baier, Ingrid, and Holland Gidney. Fish On: Seafood Dishes That Make a Splash. [Victoria, B.C.]: TouchWood Editions, 2010. 31.
9. Meyer, K. F. "Mussel Poisoning in California." Biennial Report: California. Dept. of Public Health, California State Board of Health 1929. 82-83.
10. United States Naval Medical Bulletin. January, 1911. 379.
11. Various other documents from the early 1900's.
12. Peterson, James. Fish & Shellfish. New York: Morrow, 1996. 125.

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