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Confits, cassoulets, and botulism details

People have been talking about confits (cooked fat-preserved meats) -- either canned, locally produced commercial, or home-made -- especially for use in cassoulets. A question arose about safely "aging" confits that aren't canned. There's been related Chowhound discussion before, as in chowhound.chow.com/topics/572158, but I've attempted here to gather hard data from authoritative (mostly print) sources. Including ins and outs of a food poisoning hazard I first learned about in some depth long ago when I worked in a lab that researched it.

"Botulism" poisoning comes from food contaminated by toxic byproducts of growing _C. botulinum,_ one of the disreputable, ubiquitous, anaerobic, spore-borne Clostridium bacteria. Clostridia are everywhere, and are often innocuous, until they coincide with particular conditions to produce various ills. In foodborne botulism, the problem is not the bacterium but the toxin it makes.

This toxin is deadly but fragile. Cooking to 80 degrees C (176 F) for 30 minutes reportedly destroys any of it in food. Things are different with the tough, heat-resistant botulinum spores. The spores can survive hours of boiling and other common cooking methods. Treatment with steam pressure above 120 deg C (250 F) reliably kills them, and is mandatory in commercial canning. That protection is lost once a canned product is opened, or if a confit is made and used fresh. [Temperature/time details from Merck Manual, 2006 professional edition.]

Unless its spores are completely eliminated, botulinum growth and toxin can develop in food stored with little air contact ("anaerobic"). Contrary to some claims, complete oxygen exclusion is unnecessary for this growth [Merck]. Toxin can form at refrigerator temperatures, but not when frozen (which halts bacterial activity in general). Besides freezing, standard ways to discourage anaerobic bacteria are high acid levels in some foods (not meat confits) and strong chemical preservatives.

Current popularity of poultry confits has sometimes dangerously obscured the fact that originally, like other meats preserved for unrefrigerated storage, they were very highly salted, often with nitrite or nitrate preservatives ("saltpeter"). A detailed recipe in the old Larousse Gastronomique begins by steeping a cut-up goose in a kilogram (two pounds) of mixed salt and saltpeter, and claims indefinite shelf life for the result. In sharp contrast, as Harold McGee explains ["On Food and Cooking"], most modern non-canned meat confits are made to be eaten within a few days, therefore salted much more mildly, for flavor and color, not preservation. This "few days" also coincides with published guidance on other foods subject to anaerobic bacteria.

Botulism risk rises the longer these foods are kept without freezing. While I'm no expert, the cause of every US botulism food-poisoning case I've heard of was eating (without cooking further) foods either improperly canned, or stored out of air contact (such as under fats) for more than a few days. Possibly the most publicized case was among Berton Roueché's famous "Annals of Medicine." A Thanksgiving family reunion was poisoned (with a fatality) by mushrooms marinated by boiling in white wine for 30 minutes, draining, adding spices, covering in olive oil, and storing for two weeks. An investigating public-health doctor said that the remaining contaminated mushrooms gave no warning. "They looked good and smelled good. Delicious, in fact."

In a cassoulet or other stew, long further cooking protects against any botulinum toxin in the ingredients. The real danger would be if uncanned confit, aged without freezing, were then served, tasted, or just carelessly handled, without much further cooking. That's the risk to weigh against the alternative of aging it frozen, with some possible loss of texture. Luckily, unlike bacterial growth, the chemical evolutions desired for "aging," like other food chemical processes, continue (more slowly) at freezer temperatures.

Standard biochemical data put botulism in stark perspective. Here's a comparison of rough rodent lethal dosages, in milligrams (thousandths of a gram) per kilogram body weight. The smaller this number, the stronger the toxin:

Tubocurarine ("curare"): 30 mg/kg
Sodium cyanide: 15 mg/kg
A.-amanitin (mushroom toxin): 0.1 mg/kg
TTX (in Fugu fish): 0.01 mg/kg
Botulinum toxin: 0.0000003 mg/kg (0.3 nanograms/kg)

By this measure, pure bo-tox is some 100 _million_ times more poisonous than curare or cyanide. A little dab'll do you in! (Obviously, bo-tox used medically as a muscle relaxant is greatly diluted.) That's why carelessly storing foods subject to anaerobic bacteria is like Russian roulette: You may often win, but there's more to lose.

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  1. Thank you very much for researching this. My own confits tend to be very salty indeed, and I always cook them either in their own fat to a state of external crunchiness or in a cassoulet or choucroute, just because I prefer them that way. Looks like I'd better keep doing that!

    1. very interesting. I was going to make a cassolet, but probably without confited poultry.

      1. Will, truth be told, this issue first came to my attention some years ago and I didn't take it seriously. People often raise alarm about purely theoretical food anxieties, where the anxiety itself probably causes more harm in practice. A biologist friend, who follows the research literature and is interested in food-related science, learned about confits a few years ago, and raised the issue of anaerobic bacterial risks. At the time, I thought it wasn't practically important. Confits I'd encountered or heard of were either canned and autoclaved (pph 3 above), freshly made and served soon afterwards, or freshly made and served after substantial further cooking, or in cassoulets. None of those situations suggests much real hazard. But the issue surfaced recently here on the San Francisco Bay Area board, regarding "aging" fresh confits for flavor, without freezing them. Combine this with the low preservative content of modern confit recipes, and you are starting to paint a truly dangerous scenario. Also, people can be falsely assured by anecdotal good luck. I've seen that on Chowhound, testimonials where no problem developed, but anaerobic toxins could easily have formed (for instance, garlic stored under olive oil). Then you read about something like the family poisoned by cooked spiced mushrooms kept in a similar way, and "delicious ..."

        12 Replies
        1. re: eatzalot

          Further cooking won't help. If you have active botulism spores in a friendly environment, they will reproduce and create the toxin. It is the toxin itself that is the problem, so cooking won't render your food safe.

          Its fairly easy to avoid creating botulism-friendly anaerobic environments. But yes, "preserving" food without bothering to find out how to do so correctly is a very bad idea. Right up there with not boiling unpasteurized milk.

          1. re: eatzalot

            Greetings tmso. The three C. botulinum manifestations have separate characteristics. I tried to bring this out in the original posting, I apologize if it was unclear. Spores require autoclaving to kill, but aren't normally a direct human pathogen (with occasional exceptions for infants, a different topic). They are environmentally widespread and can get into any food that isn't canned. Bacteria developing from the spores, and toxin from the bacteria, both are vulnerable to ordinary cooking (from 15 min at boiling, 100 C, to 30 min at 80 C, according to standard published guidelines, I cited one above). That's why cooking (or recooking) shortly before serving is considered a safety backstop should other measures fail to prevent this bacterial growth. Even if spores are present in friendly media, it takes time for bacteria to grow (the recurrent "few days" consumption guideline for certain stored foods; I wouldn't care to gamble on how many).

            The scenario I address is specific. Storing susceptible foods _at refrigerator temp. or above_ for more than "a few days," then consuming it with little or no further cooking, violates guidelines and good sense. I wouldn't want such stored food around at all beyond a very few days, because of the risk of someone becoming unknowingly or carelessly exposed to deadly toxin.

            1. re: eatzalot

              Seems you're right about the cooking time (or nearly). It's at odds with what I'd been told anecdotally, but it does seem that 30 min at 90 C or 15 min in a deep fryer will effectively destroy botulism toxin. The literature cites a huge range of cooking times, so I would not mess around and take the upper bound, if you're hoping to destroy possible botulism toxin through cooking.

              But as I said, you're right, carelessly "preserved" foods are just a bad idea. An obviously bad one.

              1. re: eatzalot

                Thanks tmso. I too noticed disparity in precise toxin-destroying guidelines, but not gross disagreement. Specifically:

                Roueché (an earlier source): 15min at boiling temp (100C)
                Merck Manual (2006) 30m 80 C
                CRC Handbook of Food Toxicology (2002) 20m 79 C or 5m 85 C
                World Health Organization (2002) 5m >85 C or "few min" at 100C

                The CRC handbook addresses the question in depth; upshots above. (Obviously, any credit or responsibility for these numbers vests in the sources unless I've mistyped.)

                1. re: eatzalot

                  You're right that there's not gross disagreement for how long it takes to destroy the toxin. But try looking for empirical studies (I found a few using Google Scholar). Where you see the disparities seems to be from inoculating food with the toxin, then cooking it and measuring either the toxin left, or mouse mortality.

                  And I think that's the worrying thing when it comes to confits. You have to simmer a duck leg for a long time to bring the bone and the inside of the joints up to 100 C. I know that I've had the thickest part of a leg of confit be not as hot as I would have liked when serving them. If it had been a poorly done home-preservation, that would be really dangerous.

                2. re: eatzalot

                  Nice attempt to cover a lot of material but you got a number of things very wrong.

                  1. Spores of C.bot are not very resistant to heat and it is not mandatory to use temperatures above 120C to kill them...either in home or commerical canning situations.
                  2. Toxin production occurs under anaerobic conditions (no oxygen) but is very strain specific and there are some C.bot strains that can produce it under microaerophilic conditions. Some strains can produce toxin under refridgeration conditions but most do not. Toxin production in "real world" situations (i.e. undeprocessed food products) takes v. long time (months).
                  3. Toxin production depends on a number of factors and presence of viable (recoverable) spores of C.bot does not mean that toxin will be produced. There is a lot of other factors that can and do play a role (water activity, ph, salt, nitrate/nitriate, etc.).
                  4. Once toxin is formed it can be "denatured' by cooking but the numbers I know call for at least 60 min at 100C. Many of the Merck values you quote refer to liquid toxin suspensions which is quite different from actual food products. My personal philisopy is that when in doubt...trow it out.

                  To comment on the issue of "aging confits that aren't canned":
                  A. Commercially available raw meat/poultry products will not contain C.bot spores or the level of contamination will be extremely small. This is quite different from any root vegetables or any products that grow directly in the soil.
                  B. Method of producing traditional confit (in ceramic crocks/containers - open to the air) calls for an extended cooking proces (12hrs+) at elevated temeratures of ~200F which is more than enough to kill C.bot spores.
                  C. If salt or Prague salt are used in the preparation (even at low concentrations) of the confit the hurdle that C.bot will have to overcome (spore repair and germination) in order to produce toxin is greatly increased.
                  D. Aerobic storage ("aging") at refridgerated temperatures (0-8C) for extended periods of time provided the confit has not been disturbed/re-contaminated poses v. little risk when it come to C.bot.

                  1. re: Pollo

                    Pollo, I presume your response was sincere, but some points you've raised were in my original posting or consistent with it, yet you seem to've overlooked that; others contradict standard first-recourse references that I quoted verbatim; others seem off the point, e.g. there are obvious public cases of record with poisoning from weeks, not months, of storage; and non-toxin-producing C. bot strains are irrelevant when others do produce lethal toxin. I deliberately omitted many other irrelevant details, such as principal toxin variants, their geography, and their different thermal behavior, because none of this alters the resulting food guidance.

                    Above all, anyone disputing information I've simply quoted here is not arguing with me, but with the sources I quoted -- is that not obvious? -- therefore their argument is properly directed to those sources. Moreover, on factual matters like this I always research far beyond what I post, and I didn't, therefore, cite other supporting information I consulted from the US Food and Drug Administration, Centers for Disease Control, additional reference books I have in the original, or academic experts I know and talked to about this. All emphatically support the upshots. One expert even argued privately that the toxin's particular mechanism is such that LD numbers actually understate its potential animal lethality.

                    This topic's real point transcends scientific minutiae. Do MODERN fresh confit recipes, aged for weeks or months at refrigerator temps. or higher, reliably prevent botulism? The answer from all authorities I've cited here is NO, which also implies that failing to convey this warning is irresponsible or worse. We all agree about when in doubt, throw it out.

                    1. re: eatzalot

                      eatzalot, I agree with you that we could have a long discussion about all the particular characteristics/behaviour of C.bot in different products, etc. However, I do not see how you or the "authorities" you mention can come to a conclusion that modern production methods of confit combined with refridgerated storage are not reliable in preventing botulism? What is this opinion based on?...can you provide any evidence that would support your conclusion?

                      1. re: Pollo

                        Pollo, I'm trying to be helpful but I have the same broad problem with this as with your previous posting, which as I said, raised points as if overlooking details I'd already posted. On, for example, time and temp. to safely destroy toxin in food, you contradicted food (not laboratory) advice from the Merck Manual, CRC Handbook of Food Toxicology, and World Health Organization (and others I didn't quote), all of which you were free to check and confirm.

                        I've given the basic logic two or three times in this thread. It has been clear and sound to other people including professionals. If YOU will please re-read closely here, and if you still disagree, explain precisely where you find the key error, then I can either answer, or correct it promptly and gratefully.

                        1. re: eatzalot

                          eatzalot, I am trying to understand your "logic" but have a hard time trying to understand how you get to your conclusions?

                          1. First of all I did not contradict what the Merck list but only listed values that I am familiar with.
                          2. The example you list do not apply to confis (mushrooms in oil?). Furthermore, there is a hudge difference difference between products cooked in fat (i.e. confis) and products stored/packed in oil and you imply otherwise?
                          3. It is true that some C.bot strains can produce toxin at refridgerated temperature (~4C) but those strains (majority if not all - not 100% sure) are limited to marine environments and hence marine based products.
                          4. There has not been a case (to my knowledge) of botulism due to home made confis that have been "aged" at refridgeration temperatures (0-8C). 5. The old recepies that call for hudge amounts of salt and saltpeter where fine 100+ years ago when the sanitation/meat quality/refridgeration conditions and general knowledge of this subject were poorly understood and things have progressed since then.
                          6. When you said that the "logic" you have given "...has been clear and sound to other people including professionals" who are you talking about? Who are these "professionals" (Harold McGee, biologist friend)?

                          If the risk of botulinum from improperly stored confits or even worst, sous-vide prepared products was anywhere close to the levels you suggest we would have heard about it long time ago and v. often.

                    2. re: Pollo

                      Pollo, you began by claiming offhand data (not a source anywhere) that disputes standard published spore and toxin destruction requirements in food; called confit storage "aerobic" when I wrote only of confits stored under fat; now deny even that your data disagree with (i.e., contradict) Merck Manual, yet ask to be satisfied completely? Shall I stand on one foot? :-)

                      I'll summarize the topic (4th and last time) at the bottom of this page, and give you one more comment: I prefer not to read about fatalities before citing botulism risk; and regarding sous-vide, I have you dismissing that risk, and the head of Biology at a university you've certainly heard of, warning me about it -- I'll heed the warning.

                      1. re: eatzalot

                        OK...I can see that is is not going to go anywhere. Read my post again and see what my answers were to your questions....it's quite easy to follow and all I'm doing is asking questions about your own comments.
                        1. There is only one definition of "aerobic" and that is "exposed to air". Technically a confi preparation can not be called anaerobic if it is made in an open container exposed to air. It might be possible for the interior of conit to develop anerobic conditions (I do not dispute tat) but unless you conduct inoculated pack studies to prove that this can happen and C.bot will grow and produce toxin this claim of yours is not a FACT....science deals with FACTS. 2. When it comes to outbreak data it is that kind of data that shows "real life" occurence of a problem and that kind of data needed to indicate a problem. 3. Quoteing a head of Biology at some university doesn't cut it...if he/she were a microbiologist I would have more respect....

                3. I store confitted poultry vacuum packed in the deep freezer. It has no nitrates.

                  I have never felt even slightly nervous, much less anything akin to a possibly loaded gun being jammed to the side of my head while eating a duck leg confit on a comfy bed of fried potatoes. Never. Nope. Never.

                  1. Is it only poultry? What would the danger be for say..

                    a roast joint (left overs from sunday lunch)
                    sandwich meat from a pack
                    potato salad

                    The impression I get is that all of these foods could catch the spore and harbour the bacteria. Is that correct?

                    2 Replies
                    1. re: Soop

                      Soop: unlike more common foodborne illnesses from organisms developing on food surfaces (some foods are especially susceptible to that, including dairy products), botulism is peculiar to situations where spores make contact with food and THEN are sealed off from air and allowed to develop ("anaerobically"), releasing a toxin. That's why botulism is associated with canned and preserved foods. Note the connection here: A French term for preserved foods or conserves is confiture. The foods you've mentioned would be much less subject to botulism, UNLESS you then covered them with fat, or sealed into an air-tight container. (The same concern, by the way, attends the avant-garde cooking technique of _sous-vide,_ cooking food at low temp. in airtight packages. Done improperly by non-professionals or with equipment that does not maintain just the right temperature, it greatly accelerates anaerobic bacterial growth.)

                      General information on botulism is available online from health organizations. Though less common, it has a much higher mortality rate than other forms of "food poisoning;" North American statistics showed roughly a two-thirds death rate through middle 20th century. Botulism mortality rate is lower now with better therapies, especially if correctly diagnosed, but it's still a grave illness.

                      1. re: eatzalot

                        Brilliant, thanks for replying and explaining. Although one could see it as slightly morbid, it's fascinating, and I've really enjoyed this thread so far.

                        Thanks for contributing it :)