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Botulism concerns re infused oils and confit

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#31 MaxH

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Posted 26 July 2010 - 10:48 AM

Safety question redirected from the current July 2010 "Slow cooker duck confit" thread:

interesting! I wondered about the warm setting [circa 180 degrees F]. Any sense (MaxH?) of whether or not that would create additional food safety concerns?

There are multiple types of food safety concerns. 180 F (actually, anything above about 140 F [Note 1!]) kills bacteria and larger organisms such as trichinia parasites. From the viewpoint of preventing such diseases, specific cooking temperature is of concern mainly with very low temperature cooking like sous-vide, still safe if done right.

Botulism, topic of this thread, is a separate issue, independent of all that. As I mentioned before in your Slow-Cooker Confit thread, Daniel, it actually has little to do with appliance temperature settings and more to do with what happens after cooking. That's because, not to repeat this point endlessly, killing dormant botulinum spores requires 250 F at the food itself, and you can't reliably raise water-bearing foods to 250 F without the steam autoclaving mandatory in commercial canning (in metal cans, or temperature-tolerant soft containers like retort pouches and aseptic "brick" packs). The fatal 1971 US botulism outbreak happened through inadequate pressure sterilizing of canned potato-leek soup meant to be served cold. (That incident sharply raised US awareness of botulism, which has since faded.)

Any food, regardless of cooking details, can later germinate botulism spores (which in turn create the dangerous toxin) when stored anaerobically (e.g. sealed airtight or immersed or coated with fat), unless the food (1) has high enough acid content, (2) contains strong enough chemical preservatives, or (3) was properly steam-sterilized to 250 F [Note 1]. Some C. bot. strains grow at refrigerator temps., but they don't grow instantly, and the time factor works in your favor. These details are elaborated earlier in this thread and in the official link below. Botulinum spores are remarkably tough: One famous fatal US outbreak came from mushrooms boiled for hours in wine -- which would easily kill almost any other foodborne pathogen -- then stored, cool, under oil for several days.

As also detailed upthread, modern confit recipes satisfy none of those three preventive conditions. That's why standard authoritative advice (and instruction to professional cooks) is simply to refrigerate fresh confits and serve them within a few days, or freeze (which interrupts any C. bot. growth). Heating the food thoroughly for a few minutes before serving also destroys any accumulated botulinum toxin. That safety precaution is automatic if you oven-crisp your duck, or use it for further cooking like a stew (e.g., cassoulets).

Note 1: For specifics, check official public-health guidlines such as WHO Fact Sheet 270. Do not rely on offhand advice. Some published confit recipes also neglect this simple precautionary information.

#32 Daniel Duane

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Posted 26 July 2010 - 10:57 AM

thanks, MaxH

#33 slkinsey

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Posted 26 July 2010 - 02:34 PM

Thanks for the info, Max. Could you describe a duck leg confit recipe that you think contains sufficient salting to make the product reasonably safe long-term in a refrigerator? And also, do you think such a product could be used the same way most of us are used to using confit (e.g., crisped in the oven with potatoes) without being horribly salty?

For my sous vide confit, I've always liberally salted the duck legs for around 24 hours, then rinsed them off, patted dry, bagged and cooked.
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#34 Yajna Patni

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Posted 26 July 2010 - 04:53 PM

what about oil pickles? I have made and eaten these for most of my adult life, as have lots and lots of Indian people, and any one who buys a jar of mango pickle at the Indian store. I have usually used green mango or lime, which both have a certain amount of acidity, but there are many pickles that do not have that... i have made carrot and garlic and drumstick.

#35 MaxH

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Posted 27 July 2010 - 02:54 PM

Sam, as a general reminder, most of this thread's existing content is in earlier postings (what I wrote yesterday just re-summarizes, answering a request on another thread). What I have about salt preservation appeared around this post and contrasts old, pre-refrigeration French confit recipes (I have some, and an example is in the linked posting) and modern recipes; Harold McGee also emphasized this difference.

With the disclaimer that I'm not a source of any of this information, just a messenger, the buzzword for your specific question is "curing." As I recall the history, the main reason saltpeter cures (nitrates, nitrates) came into use originally, hundreds of years ago, was to prevent botulism; I believe plain salt works too, but at a higher concentration (and with more degradation of the meat over time from other factors). For real information I refer you again away from any offhand advice whatever, and to the Usual Sources (public advisories). In a brief check, I found a useful-looking overview with data, assembled by the University of Georgia (US), Here, and other authoritative info is surely abundant. I began checking US FDA, but a major revision to its useful CFSAN central site has broken external links to it. But you can search countless food topics directly at http://www.fda.gov/Food and especially http://www.fda.gov/F...ety/default.htm .


Yajna, all I can offer to your comment is that one condition I quoted above that prevents C. botulinum growth is moderate food acidity (pH 4.6 or below is the standard official number), which occurs automatically with many fruits. It's done artificially with some processed foods (pesto sauce, some preserved vegetables) by adding fruit-type acids, and the amount needed is small enough that many foods can tolerate it without changing flavor much. That too I believe appears earlier in this thread. Proper pressure sterilization as described above will also eliminate the issue. Please read the (international, multilingual) WHO Botulism Fact Sheet linked in my previous posting. Processed foods not meeting listed conditions can develop botulinum toxin (people in the US have died from various homemade preserved vegetables) and would bring health department enforcement if done commercially. ("I've done it many times without harm" is a distracting false comfort ignoring the reality of the situation. The Italian-immigrant patriarch who died from his oil-preserved mushrooms, mentioned earlier, and sickened his relatives, had also served them often before without ill effect; he finally drew the loaded chamber in the metaphoric Russian Roulette.)

#36 MaxH

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Posted 27 July 2010 - 04:28 PM

saltpeter cures (nitrates, nitrates)


Sorry, meant to write (nitrates, nitrites). N.B., Nitrates convert biochemically into nitrites anyway, when used as preservatives. After data emerged in the 1970s about carcinogenic nitrosamines forming in meats preserved this way, standard practice changed to (1) limit the nitrite amount, (2) stop using nitrates entirely, and (3) add antioxidants like erithrytol or ascorbic acid (Vitamin C). It seems that some of the same chemistry happens naturally in certain well-established safe vegetables too (like lettuce), but there the natural presence of antioxidants like ascorbic acid counters the harmful effect.

In recipes and older general writing, "salt beef" or "salt pork" means beef or pork cured with nitrites/nitrates, because that worked much better than plain salt. "Corned" beef is another term for salt beef (but with more specific connotations).

#37 MaxH

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Posted 28 July 2010 - 06:03 AM

...Could you describe a duck leg confit recipe that you think contains sufficient salting to make the product reasonably safe long-term in a refrigerator?

I didn't ask before, but why are you interested specifically in long-term refrigerator storage?

Why not just salt your confit for flavor as the modern recipes routinely do, refrigerate for brief storage and freeze for longer storage? Those are the instructions for storing commercially made fresh confits also.

Without any anti-botulism steps, refrigeration is still reliably safe for a few days (the upper limit seems to be two weeks, anyway that's a legal limit in US regulations for commercial food -- I think it's in Title 9 CFR 424.21, which has many such details).

Refrigeration is still safer than storage at higher temperatures because fewer C. botulinum strains can grow at refrigerator temperatures, and those are more associated with seafood and marine soils.

#38 bmdaniel

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Posted 28 August 2010 - 11:55 AM

I was thinking about this today and had a question - on garlic infused oil, what about infusing with garlic and then removing the garlic and ensuring that the oil goes to a sufficiently high temperature after removal (say 300 degrees). You could use whole cloves to ensure adequate removal.

I am not planning to eat any garlic infused oil that wasn't freshly prepared (don't use much in the first place), but was curious about this from a theoretical perspective.

#39 MaxH

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Posted 03 September 2010 - 12:45 PM

on garlic infused oil, what about infusing with garlic and then removing the garlic and ensuring that the oil goes to a sufficiently high temperature after removal (say 300 degrees).

Sounds reasonable to me -- essentially an improvised ultrahigh-temperature (UHT) sterilization. (Applied industrially for very short intervals to liquid foods piped through small tubes, if I recall, so the temperature can be raised and lowered fast, though I think it's aimed mainly at bacterial pathogens; sporeborne Claustridia might require longer heating as well as higher temps. -- I'm just speculating here.)

A downside would be a factor that brings criticism to UHT foods even at lower temps.: Not just pathogens but flavors and aromas are vulnerable to heat. Water departs as the oil temp. rises above its boiling point, but the same also happens at various temperatures to the organic components that make up flavor and aroma, and they'll also tend to react more, and oil rancidity (oxidation) accelerates at higher temps. That's actually how they make the "drying" vegetable oils that are the basis of traditional oil paints and printer's inks.

But as you indicated, bmdaniel, it's theoretical, because either fresh preparation or freezing addresses the spore hazard without throwing out the flavor.

#40 BadRabbit

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Posted 06 February 2011 - 03:21 PM

I know this post will cause some backlash but here goes.

There are usually 20-30 cases of Botulism a year in a country of 300 million (and a large number of these cases seem to occur in a very specific part of the country).

Is this really something we want to worry about? Frankly, I'm not going to make a bunch of herb and garlic oils if I have to throw them out soon after making them (I don't use them enough to run through a whole batch within the guidelined period and it's not worth making the effort to make micro batches). Is the risk significant enough to give these things up? I really don't think it is.

Before anybody starts in with the "but it's deadly and it just requires timely disposal\proper procedures\ etc..." I would like to compare it to something most of us do everyday, namely driving. Wearing a helmet while driving has been shown to significantly improve survivablity of high speed automobile crashes. Does this mean I'm going to start wearing a helmet when I drive on the interstate? Of course not, because it is a PITA and the probability of having a high speed accident is fairly low and an accepted risk.

In addition, there are certain things that are materially changed by the procedures needed to make them 100% safe. Pesto is a considerably different product if it's pressure canned or acidulated. The same can be said of garlic oils.

People have kept pestos and the like for long past FDA guidelines (and sans refrigeration) for generations. It seems ridiculous that in the modern age so much time, effort, and fear is invested in something that occurs so seldom.

#41 IndyRob

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Posted 06 February 2011 - 04:21 PM

I know this post will cause some backlash but here goes.

Bad rabbit. Bad, bad rabbit. :raz:

I think in a previous thread I got freaked out about this and did some googling and found a similar statistic. While I don't intend to repeat this practice after that, I've often used room temp infused garlic oils after six months or more (although always heated to frying temps when used), I don't think it's a necessarily bad thing to put the problem into perspective.

Given the fact that I'm still alive, and that I hear more about salmonella problems than botulism, I can't help but feeling that there might be a Douglas Baldwin-esque (in reference to his conviction that lower cooking temps can be proven safe) admonition lurking in the wings.

I am making no claims, just acknowledging a data point that seems oddly out of place.

#42 ermintrude

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Posted 06 February 2011 - 04:25 PM

By the way, even this food Web site has carried reckless advice to take Acetaminophen (a drug lately in the news) when you have a partially impaired liver!


Actually they are correct, in the majority (If a person has not been drinking heavily) of cases Acetaminophen is one of the safest drugs to take with a partially or even seriously impaired liver. Provided the body has enough glutathione then Acetaminophen is broken down into harmless metabolites however if the body runs out of glutathione then a diferent metabolic path is taken and one of the metabolites is toxic and kills liver cells. Glutathione can be depleted by ethanol consumption, excessive doses of Acetaminophen and or malnutrition. So provided that a person is well nourished, no more than 1g four times a day taken 4 hours apart and for several days and not drinking alcohol to excess then Acetaminophen is the way to go. The other pain killers Aspirin Ibuprofen etc are NSAIDS, these can thin the blood, cause bleeding and in people with partially or seriously impaired liver cause a lot more problems.

Often Acetaminophen poisoning is accidental, by taking 4g a day for to long, mixing medications without reading the ingredients and so going over the 4g per day limit, drinking alcohol and taking paracetamol and by the time the damage is done it's to late. In known overdose situations get to a hospital ASAP.

You can replenish glutathione levels by taking NAC (N-Acetyl-Cystene), and this is the antidote, given IV quickly enough to Acetaminophen poisoning. Unfortunately NAC smells of rotten eggs so it's not a popular supplement but perhaps one to consider if you know you will be drinking more than a few drinks.

All that said, if you have a partially impaired liver then you should follow your doctors advice.
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#43 MaxH

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Posted 07 February 2011 - 12:56 PM

Taking some recent points in order (I split off ermintrude's in a separate posting):

BadRabbit raised excellent point (going way beyond botulism, by the way) of reasonable response to unlikely risks. I've confronted these too. E.g., driving over steep hills to the ocean for waveriding in Northern California where Great White sharks attack rarely but occasionally, our talk is of those -- not the far more frequent violent crashes on the highway we're driving, with mountain-clueless drivers demonstrating reckless behavior daily. Yet we recognize both perils, and avoid needless risks with either.

IMO the question was never whether to "worry about" anything. It's whether to follow safe practices already mandatory for US restaurants (flowing from updated FDA "Food Code") after garlic-in-oil moved from a niche to a frequent restaurant practice, and botulism cases followed. BadRabbit cited botulism infrequency, not mentioning that those are numbers with enforcement of the same food-prep regulations that BadRabbit prefers to overlook. (Also I don't run into any problem myself making fresh batches as needed, and freezing extra, which also inhibits hazards as described upthread, and I've done it anyway for many years simply to preserve flavors.)

Also, please read practical details in related Pickles thread re actual taste of acid level pH 4.6 which inhibits C. bot. A food pH of 4.6 is only slightly into perceptible sour range. Quantitatively equivalent to 400:1 dilution of pH 2.0 lemon juice, about one lemon's juice (50ml) in five gallons (20 liters) water, or around "100x less acid than the market-leading Cola drink" [dougal]. This acid level occurs naturally in many foods (including, I'm guessing, many pestos with fresh basil). Commercial products strongly over-acidify for large safety margin -- again a separate issue, which shouldn't distort our notions of how "sour" these foods actually need to be for safety.

#44 MaxH

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Posted 07 February 2011 - 01:16 PM

By the way, even this food Web site has carried reckless advice to take Acetaminophen (a drug lately in the news) when you have a partially impaired liver!

Actually they are correct ... (If a person has not been drinking heavily)


ermintrude: Whole context of my comment that you quoted was specifically the perennial armchair advice to use acetaminophen ("APAP") after heavy drinking. You can find this in past eG "hangover cure" discussions if you look.

APAP as a "cure" for heavy drinking is one of those persistent misinformation points (often shortly before New Year's Eve) despite ample public cautions, obvious e.g. on googling word pair acetaminophen + alcohol. Two accomplished (and food-engaged) professor friends, a biochemist in the US Northeast whose textbook you might know, and an organic chemist in the Midwest, have joined me in posting warnings in past Decembers to US food-drink Web sites (and newspaper food editors). Further from the same biochemist:

The lethal dose of a drug divided by its effective therapeutic dose is the Therapeutic Index (formerly Therapeutic Ratio). We are happy if that number is something like 1000. We are not happy if it's 2 or less, a narrow T.R. means people are going to get hurt. With Acetaminophen, if someone has a bit of liver impairment, the T.R. can approach 1. Drinking uses up certain cofactors in the liver and makes the problem worse. I've almost completely stopped taking Tylenol because of the probable temporal proximity to alcohol. / In fact I wrote a rather strongly worded Q and A in the Companion book ...

On some food-drink sites I added background on the further issue of the controversially uniform alcohol warnings that US FDA added to NSAID labeling in 1998 (21 CFR Part 201, all public in the US Federal Register):

A number of comments said the established risks of acetaminophen use by heavy alcohol users far outweigh the risks of aspirin use by the same consumers. One comment submitted data from a comparative risk analysis of aspirin and acetaminophen (Ref. 66). Based on this analysis, the comment maintained that the number of expected deaths from acetaminophen toxicity when used for the short-term treatment of fever and pain is 12 times higher than that expected with aspirin. / Several comments complained that despite the much greater risk for acetaminophen, the proposed alcohol warning conveys the impression that for heavy alcohol users, the hazards of acetaminophen use and aspirin (or NSAID) use is essentially the same. Thus, consumers may be led to believe that they face a comparable risk with either analgesic. The comments said the proposed warning minimizes the essential messages.

I'm responding to your remarks here, ermintrude, but please start a separate thread (and first review past eG discussions in the Spirits forum) if you wish to pursue this side topic further.

#45 andiesenji

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Posted 07 February 2011 - 01:19 PM

Long ago I posted about the oven-roasted garlic in oil that I prepare in large amounts and can in jars so it can be stored at room temp.

I only use the peeled garlic cloves sold in the big containers at Sam's or Costco or Smart & Final, not garlic from my garden.

I stab one of the largest garlic cloves with the probe of my thermometer/timer with it set for 250° F.

I cover it with two liters of olive oil and put it in the oven at 325°to 350°F. It will take quite a while for the thermometer to sound the alarm, meanwhile the entire house (or neighborhood) will have the "aroma" of garlic.
I have also tried doing this in a deep fryer but did not like the texture of the garlic, it cooked too rapidly and was hard on the outside. The longer oven cooking produces a much nicer result.

I have also tried speeding up the process by heating the oil partially before pouring it into the deep roaster but I think that can be a bit chancy unless one has a very steady hand. (I no longer do.)

When the alarm sounds, I set the timer for 15 minutes and at the end of this I turn the oven off and allow the stuff to cool a bit.
I then transfer it to pint jars, some garlic and some oil in each one, cap them and let them cool completely.
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#46 MaxH

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Posted 07 February 2011 - 01:57 PM

andiesnji, you can also do this reliably and rapidly in the type of pressure cooker designed for home-canning botulism prevention. Same type used routinely for safe canning of non-acid foods. It's distinct from the more common home pressure cookers that simply speed up ordinary boiling or steaming. Friends have been doing this, and are happy with the flavors.

Your thermometer method may achieve the result, but only if the garlic loses all its moisture. As I mentioned after your earlier posting on this, the thermodynamically powerful self-regulation that water imposes prevents food from reliably going above 212°F, regardless of cooking method, at normal atmospheric pressure until all water is expelled. Raising the pressure gets around this problem.

Though I've not seen your set-up, as a longtime user of many kinds of thermometers for sometimes critical technical measurements, and for cooking, I'm concerned that a reassuring reading of probed garlic could possibly do what I've seen food thermometers do in some other situations: conduct heat to the actual sensor point from parts of the probe outside the garlic. In other words, the spot in the clove where the thermometer is may be reliably 250 °F (120 °C) but the thermometer probe itself distorts this picture, and other garlic cloves remain below 250. That (which by the way has counterparts in all sorts of other temperature measurement situations) is difficult to rule out, unless it's a small point probe enclosed entirely within the garlic, connected only by well thermally-insulated wires to the rest of the electronics in the thermometer. As a consulting engineer I could not conscientiously "sign off" to the system as described, which is not to say it may not still work with luck. I'm confident of the pressure cookers though, that's also how commercial canners routinely prevent botulism.

#47 BadRabbit

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Posted 07 February 2011 - 02:02 PM

IMO the question was never whether to "worry about" anything. It's whether to follow safe practices already mandatory for US restaurants (flowing from updated FDA "Food Code") after garlic-in-oil moved from a niche to a frequent restaurant practice, and botulism cases followed. BadRabbit cited botulism infrequency, not mentioning that those are numbers with enforcement of the same food-prep regulations that BadRabbit prefers to overlook. (Also I don't run into any problem myself making fresh batches as needed, and freezing extra, which also inhibits hazards as described upthread, and I've done it anyway for many years simply to preserve flavors.)


Even before pressure canning was available to the home cook in the US(the first home pressure canners were introduced in the US in 1917 and it was much later before it was widely used in homes), botulism was a fairly rare food borne illness. CDC numbers show very little change in the number of cases per year from 1899-preset day. The population was less than a third of today's poulation in 1900 but the incidence of home canning was MUCH more prevelant that it is today. I can't find exact numbers on canning prevalence but I would be willing to bet it easily offsets the difference.

In 1900 the actual incidence rate was 1.18421053 × 10-7 or roughly 1 in every 8.5 million people would get botulism per year in a time where home canning was being done at many times the rate it is now (1). That doesn't seem to be a big concern to me. Couple that with the fact that more than half of the cases are from the west coast and it doesn't seem a very likely danger to me in Alabama.

I am not suggesting that commercial food producers should ignore these guidelines. It would be disastrous if they did and there was a problem because it would possibly infect huge numbers of people. I just think it can be mostly ignored by your typical person at home making an occasional flavored oil or pesto.


http://www.cdc.gov/n...es/botulism.PDF

Edit: Added footnote
(1) To give an idea of a similarly dangerous activity, an automobile occupant's odds of fatality during a 30-minute drive are 1 in 8.5 million (and most of us engage in this activity 2-3 times a day).

Edited by BadRabbit, 07 February 2011 - 02:24 PM.


#48 MaxH

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Posted 07 February 2011 - 02:39 PM

Again BadRabbit you cite valid information, but a selective, rhetorical picture. And again, I'm not arguing that anyone is going to get botulism, rather to be aware of risks and precautions. Sensible precautions that many of us have found easy to incorporate reduce the small chance to essentially zero which (since you like such numbers) constitutes a near-infinite risk reduction ratio.

I've noticed for years that public information on any aspect of this topic on any food form, even with far narrower and more moderate information than in this thread, always generates responses confidently rationalizing familiar practices. Fine, that's individual choice. But make it an informed choice, and be aware that all of the episodes I know in detail of US botulism outbreaks were first-time surprises to people who previously "did it this way many times" without problems.

Historically, botulism has been a threat as long as people have canned foods and it was a major factor in the popularization of "salt" (i.e. nitrite or nitrate, which is a nitrite precursor in this application) curing of meats hundreds of years ago. Until dedicated home pressure cookers were available, people were much more selective about what and how they preserved foods! Countless fruits and many vegetables (I mentioned pesto sauce as possibly another case) were empirically known safe to can with only boiling-water sterilization. I have more cookbooks than most people reading this, and as already mentioned in this or a related thread, the point about selective home canning has been explicit in cookbooks for generations. The situation is different now, when it's fashionable to store things like garlic or duck under fat, without the nitrite or extremely heavy saline preservatives common in old traditional confit recipes. The internet now carries some recipes much riskier than anything I've seen on eG, posted by people who appear utterly unaware of any food safety issues at all and it's those recipes that spur threads like this one.

#49 andiesenji

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Posted 07 February 2011 - 03:24 PM

andiesnji, you can also do this reliably and rapidly in the type of pressure cooker designed for home-canning botulism prevention. Same type used routinely for safe canning of non-acid foods. It's distinct from the more common home pressure cookers that simply speed up ordinary boiling or steaming. Friends have been doing this, and are happy with the flavors.


Thanks for the advice but I really do know a bit about it.
I'm almost 72 years old and have been canning since my twenties, having grown up on a farm where everything was canned, including meats.
Even pressure canned foods can be affected by botulism if care is not taken.

Many years ago when the possibility of irradiation of foods immediately after harvest became available I spent a lot of time writing to the various government agencies because this would certainly remove completely the possibility of botulism.
Unfortunately some people believe that this is bad and they have a lot of political clout so we are still in the dark ages on this subject.

I have the largest pressure canner made by All American (41 quart) but I need help when using it and no longer have a live-in housekeeper. I also have a smaller one that holds 7 pint jars and this is the one I use when canning the garlic in oil.

Just canning it does not give the "roasted" flavor that I want.
I don't like the flavor of raw garlic infused in oil which is why I roast it to begin with.

I consulted the Farm Bureau office in my city when I first moved up here in '88 and was given a stack of printed materials about all facets of canning, including botulism and etc.
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#50 Lisa Shock

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Posted 19 February 2011 - 10:26 PM



IMO the question was never whether to "worry about" anything. It's whether to follow safe practices already mandatory for US restaurants (flowing from updated FDA "Food Code") after garlic-in-oil moved from a niche to a frequent restaurant practice, and botulism cases followed. BadRabbit cited botulism infrequency, not mentioning that those are numbers with enforcement of the same food-prep regulations that BadRabbit prefers to overlook. (Also I don't run into any problem myself making fresh batches as needed, and freezing extra, which also inhibits hazards as described upthread, and I've done it anyway for many years simply to preserve flavors.)


Even before pressure canning was available to the home cook in the US(the first home pressure canners were introduced in the US in 1917 and it was much later before it was widely used in homes), botulism was a fairly rare food borne illness. CDC numbers show very little change in the number of cases per year from 1899-preset day. The population was less than a third of today's poulation in 1900 but the incidence of home canning was MUCH more prevelant that it is today. I can't find exact numbers on canning prevalence but I would be willing to bet it easily offsets the difference.

In 1900 the actual incidence rate was 1.18421053 × 10-7 or roughly 1 in every 8.5 million people would get botulism per year in a time where home canning was being done at many times the rate it is now (1). That doesn't seem to be a big concern to me. Couple that with the fact that more than half of the cases are from the west coast and it doesn't seem a very likely danger to me in Alabama.

I am not suggesting that commercial food producers should ignore these guidelines. It would be disastrous if they did and there was a problem because it would possibly infect huge numbers of people. I just think it can be mostly ignored by your typical person at home making an occasional flavored oil or pesto.


http://www.cdc.gov/n...es/botulism.PDF

Edit: Added footnote
(1) To give an idea of a similarly dangerous activity, an automobile occupant's odds of fatality during a 30-minute drive are 1 in 8.5 million (and most of us engage in this activity 2-3 times a day).


But, in 1900 the average lifespan was under 50 years. Diagnostic tools were not well developed at that time, meaning that deaths were often mis-diagnosed and undocumented. Garlic oil and pesto were not commonly produced in American households in 1900.

Edited by Lisa Shock, 19 February 2011 - 10:35 PM.


#51 technophile50

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Posted 21 February 2011 - 02:53 PM

All the water doesn't have to be removed. An important parameter for the growth of spoilage and pathogenic organisms is "water activity", Aw, the ratio of the water vapor partial pressure of pure water to that of the food.[1] Various solutes lower the vapor pressure - salt(s), sugars, free amino acids(e.g. fish sauce), and drying foods concentrates these things and decreases Aw. Botulism requires an Aw of 0.85 or above. I found a reference which said that carrots dried to 39% moisture had an Aw of 0.81. The solutes available in garlic would concentrate and lower the vapor pressure in a similar fashion, but to be safe Aw would have to be measured. 250 F for 15 minutes in hot convecting oil at atmospheric pressure like andiesenji does is likely drying the garlic to safe levels, as well as inactivating the spores. It would be interesting to weigh the garlic plus the oil before & after, to see how much water was lost and oil taken up by the garlic.

Note: the Aw is a function of temperature, so something that is partly dried and safe in the fridge may not be safe in the pantry.

Ethanol at 6% will prohibit c. botulinum[2]; Ironically if the unfortunate Italian gentleman hadn't boiled off the alcohol, he might have been safe. The partition coefficient for ethanol in olive oil/water is 2.46, so storing vodka soaked garlic under oil would tend to reduce the EtOH concentration in the garlic. A mix of 50% 192 proof rum and olive oil would likely be safe, (depending on the volume of garic, and whether it started with EtOH or just raw) and interesting tasting.

Acidification below ph 4.6 is safe, but a little tricky[3] - "acidifying garlic in vinegar is a lengthy and highly variable process; a whole clove of garlic covered with vinegar can take from 3 days to more than 1 week to sufficiently acidify."

[1]http://extension.psu.edu/food-safety/food-preservation/issues/water-activity-of-foods/water-activity-of-foods-table
[2]http://www.ncbi.nlm.nih.gov/pubmed/12696684
[3]http://anrcatalog.ucdavis.edu/pdf/7231.pdf

#52 technophile50

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Posted 21 February 2011 - 03:43 PM

I read the wrong chart. The partition coefficient for ethanol in oil/water is 0.05, so most of the ethanol will stay in the water phase.

#53 MaxH

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Posted 22 February 2011 - 01:10 PM

Great data, techno, thanks! This goes deeper than the usual rudiments I find in the standard public advisory sources and books.

Water removal to prevent growth of Claustridia in garlic is a new angle here. I'd mentioned 250°F oil processing only from the consideration of spore destruction, and responding to a long context, not limited at all to eGullet, of writers seeming to confuse cooking-medium temperature with cooking-food temperature. As if hot oil or an oven at 350°F, for example, implied temperature at or in the garlic of 350°F over the same interval. That overlooks water's vaporization enthalpy (Lvap) tending to limit temperatures to 212 °F until most of the water is expelled. (A secondary point was the practical difficulty of instrumenting a garlic clove to measure internal temperatures undistorted by surrounding cooking oil. Maybe someone already has done that measurement rigorously, it would be great to find a report.)

#54 Arey

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Posted 31 July 2011 - 04:49 PM

I made a batch of pesto last week, from my bumper basil crop. I have a recipe which I print out when making pesto. Not so much to follow but as a reminder of all the ingredients. I freeze some when it's still a thick paste and before I add the cheese. The remainder I refrigerate with a thin layer of olive oil on top. The recipe I use to remind me of the ingredients says I can keep it up to 3 weeks in an air tight container as long as I keep a thin layer of oil on top. Another recipe says I can keep it up to two weeks. However, there's raw garlic in pesto, and it's in an anaerobic environment so what's to prevent botulism from developing in it? One web page I read says to only keep it in the refrigerator for 2 to 3 days.

Edited by Arey, 31 July 2011 - 04:55 PM.

"A fool", he said, "would have swallowed it". Samuel Johnson


#55 MaxH

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Posted 31 July 2011 - 06:30 PM

I made a batch of pesto last week, from my bumper basil crop. I have a recipe which I print out when making pesto. Not so much to follow but as a reminder of all the ingredients. I freeze some when it's still a thick paste and before I add the cheese. The remainder I refrigerate with a thin layer of olive oil on top. The recipe I use to remind me of the ingredients says I can keep it up to 3 weeks in an air tight container as long as I keep a thin layer of oil on top. Another recipe says I can keep it up to two weeks. However, there's raw garlic in pesto, and it's in an anaerobic environment so what's to prevent botulism from developing in it? One web page I read says to only keep it in the refrigerator for 2 to 3 days.


Hi Arey, it's a very reasonable query and I also make the stuff myself sometimes. (Generally freeze it, and other flavored oils and butters, for keeping -- habit I developed 30 years ago, originally just to best preserve flavor long-term, in which case the issue doesn't come up.)

I'd sum up the situation in my assessment as: Many recipe guidelines that I read, like the 2-3 week examples you quoted, reflect some more common spoilage risk (mold, oxidation, etc.) and have not even considered botulism because it isn't on people's minds, and is comparatively rare. (The gun in the "Russian roulette" botulism-hazard game has many, many cylinders, but unfortunately, unlike many spoilage mechanisms, one of them is loaded with a lethal bullet unless specific conditions are met.) I wouldn't rely on recipe instructions, unless they discuss this exact issue, any more than I'd rely on amateur Internet advice, to prevent something as potentially serious as botulism.

Near me the Costco "warehouse store" chain has a role as a source not just for cheap products by the ton but also some outstanding ingredients for local food fanatics and restaurants because it contracts with first-class suppliers (artisanal cheeses for example). It has sold, off and on, a good house-label freshly-made refrigerated pesto sauce, clearly not steam-sterilized because it doesn't look or taste "cooked" like supermarket jar pestos. It, like many other fresh condiments whose labels I've checked, includes a touch of citric acid or some other such food acidifier, not really enough to affect taste noticeably. I assume it's for this reason, to get the acidity throughout the product to the range that prevents botulism. (This or a related eG thread has the lemon-juice dilution example illustrating how mild the acid can taste and still give the safe pH range). But it's made by professionals who, unlike me, know exactly how to guarantee its safety.

If someone found and pointed to a truly authoritative (like, USDA, WHO, or EC Health Ministries) manufacturing guideline for that technique, it might be useful even for home cooks -- I speculate. I haven't researched this -- the info may be easily available in standard online food-safety info of the kind the USDA and related bodies have published for generations, originally in paper form.

#56 Jenni

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Posted 01 August 2011 - 12:04 AM

Hi Arey,

If I were you I would not keep the pesto longer than a couple of days, just to be on the safe side.

As MaxH says, botulism is rare ("I've made it that way hundreds of times and I never got sick...") but when it does occur it is very serious. Actually sometimes when you look online you find a lot of people being very scornful about it and saying that their Grandma did x such and such a way and lived to be 100, and how can botulism really be so serious, etc. Take it all with a pinch of salt! When botulism strikes it can claim lives because people weren't expecting it! They had done something the same way for years and had got away with it, so when they got sick they never thought it could be botulism. And it seems that many cookery writers don't even consider botulism when writing recipes for home preserves, so don't necessarily rely on instructions from a book either.

All the commerical pesto I have seen includes citric acid to acidify the product and make it safe for longer storage. I think it would be difficult to guarantee any kind of safety if you did this at home on a casual basis though, unless you had some pH strips lying around and were able to test the product thoroughly. So my advice is to enjoy the product fresh, sharing it with friends and neighbours if necessary (ask them to use it quite quickly - don't want you to kill of the neighbours now do we!) and let that be it.

#57 MaxH

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Posted 01 August 2011 - 09:15 AM

To elaborate on two points Jenni cited:

1. I DO always have pH strips lying around, and access to fancy scientific equipment if necessary (and have scientific university degrees and experience, though am no food scientist). General chemistry training and tool access do not qualify me to guarantee my pesto sauce meets food-safety standards -- it's a specialized complex subject. Example: it's easy to test pH of water-based liquids drained from a pesto sauce (note that as explained on eG, upthread I think, the correct method is an electronic pH meter if the liquid is colored, which can throw off the reading of paper pH strips). But pesto sauce is a complex compound colloid with water, fats, solids, vegetable fibers, and emulsifiers (garlic juice). An expert would know what conditions guarantee that none of those media remains friendly to anaerobic pathogens. Since that happens commercially, again I suspect there may be authoritative public guidelines and if they were handy (or if someone had the patience to search things like the ever-changing US FDA information corpus with its periodically revised URLs), it might clarify what the mathematicians call "necessary and sufficient conditions." You can always freeze the stuff soon after you make it, that doesn't kill Claustridial spores, but does keep them from developing to live organisms which in time could generate the chemical toxin.


2. The scorn and skepticism Jenni mentions, also visible sometimes on eG, likely comes from people who did not experience anything like the following:

(a) About 1970 as an adolescent I first read Berton Roueché's classic account, titled "Family reunion" IIRC, it's in some Roueché anthologies) of the Italian-immigrant patriarch who'd always made his spiced mushrooms in oil with no problem, until it killed him and sickened his family w/ botulism and left an investigating public-health doctor marveling at the absence of spoilage cues -- the toxic mushrooms looked and smelled very appealing. Then:

(b) In 1971 (IIRC from a defective sterilizer -- in those days I don't think the rigorous temperature measuring and logging were required in US food preparation as today) the Bon Vivant specialty soup company inadvertantly distributed a batch of canned potato-leek soup, meant to be served cold, containing lethal amounts of botulinum toxin. Overnight the US media were full of botulism-prevention tips. For a time, people looked differently even at foods like canned green beans. Then:

( c) In 1972 I happened to get a lab-assistant job in a biology laboratory whose library was full of books on subjects like that. Once over a sandwich, I perused one of them full of photos of botulism's effects on people (not recommended for mealtime reading).

(d) Being interested in all kinds of food, I've had several lengthy instructive personal experiences of other foodborne pathogens, which does tend to make one more aware in general.


I hammer on this subject only after emergence of certain fashionable cooking ideas in the US with limited history in the culture -- made often by people too young to recall the widespread 1971 US botulism outbreak. Herbs in oil began this thread. Some modern online confit recipes specifically -- light salting, casual cooking, "OK to store for weeks at room temperature" -- would make any restaurant health inspector's jaw drop, and I (and even people I talk to who are experts) wonder if the US is setting up for another enlightening tragedy. Needlessly, since a little awareness can safely let you enjoy your favorite pesto recipe.

#58 Arey

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Posted 01 August 2011 - 04:15 PM

Thank you both for your responses. I'll keep on with my policy of keeping it refrigerated, and after this batch is gone, not even keep it for a week.Next time I make it, I'll freeze more, and only keep some refrigerated for a day or two. I've been trying to convince myself to buy a mini-food processor, and just make pesto the day I want to have penne with pesto.

I've researched this issue intensively on the web, and was surprised to see how many people are still saying its perfectly safe to keep garlic cloves in oil for weeks. I also tried calling the FDA this morning, and should they ever want to issue a warning about being "on hold" for over an hour and a half since it can cause hand cramps and stiff elbows they can use me as an example.

MaxH - I read the same book, as a result of which I always wash new jeans twice, never graft tomato plants to jimson weed rootstocks, and can't see the name Huckabee without thinking of hogs. :laugh:
"A fool", he said, "would have swallowed it". Samuel Johnson


#59 zaskar

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Posted 01 August 2011 - 09:44 PM

I used to use fresh herbs. But now I use dried, I find that is safer. I always store it in the fridge. With fresh herbs I used to notice a slight film at the bottom of the container, I haven't seen that with the dru herbs.

Haven't had the problem with garlic olive oil.

I heat the oli to about 220-250, five minutes or so, let it cool down then strain and put it in a ball container.

#60 Blether

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Posted 01 August 2011 - 10:31 PM

It's worth reading up (it's possible online) about the science behind commercial canning, and "T" times, if I remember the terminology right. It helps to give the kind of understanding of probabilities & risk that NASA abandoned in the period before its 7-up disaster. (I mean, a blind statement of "100% safety" may be an effective PR tool, but to actually enforce the same attitude as a practical approach on the engineering side ?!)

There are different strains of C. Botulinum, with different low-temperature-resistance, but what I took away from a day or two's down-time research was that pretty much anything that starts out fresh will be safe for 2-3 weeks in the fridge. Please make your own judgment. The bacteria and the toxin are both destroyed at temperatures below 212F - it's the spores that are the danger.

You can avoid ever being in a plane crash by never flying: and jeez, you wouldn't want to have to look at pictures of plane crash victims.

That said, naskar, for room temperature and/or longer-term storage, 5 minutes at 220F is marginal at best, and at 250F only borderline.

QUIET!  People are trying to pontificate.






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