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Lisa Shock

Botulism concerns re infused oils and confit

69 posts in this topic

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

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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.

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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.)

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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 (log)

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

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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.

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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.

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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.

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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

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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.

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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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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.

Two things:

*If the oil got contaminated with botulism it would not be visible, so visual clues such as you noticed are not helpful. I don't think dried or fresh herbs would make a difference in this case.

*I'm pretty sure someone here once explained that even if you heat the oil itself up to a high enough temperature to destroy the spores, the stuff in the oil does not heat up to that same temperature so it does not mean that the product is safe. Something about waters boiling point being 100 and you can't make water go higher than that unless you heat it under pressure? God I don't know, someone help me out here. I remember that the key point was that heating it up (not under pressure) is not helpful.

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I used to use fresh herbs. But now I use dried, I find that is safer. ... 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.

Zaskar, evidently you are thinking of hazards different from the topic of this thread. With botulism you don't, in reality, empirically have any idea whether anything is "safer" or not, nor whether you've "had the problem with garlic olive oil," unless you catch the food poisoning, in which case you may improve your chances of survival beyond the classic 50-65% with prompt medical attention for the strange neurological symptoms you'll experience. For preventing botulism, the heating-the-oil comment above repeats a gross misconception addressed before in this thread and elsewhere in eG.

Folks -- please, please, read this whole thread! before repeating misconceptions already addressed here.

There are different strains of C. Botulinum, with different low-temperature-resistance

Yes, I have that information in depth, in print, and it's behind my comments here. For example, selections from much more info in a current standard authoritative physicians' reference (the professional Merck Manual, emphasis to distinguish from other Merck pub'ns with related titles):

Seven ... antigenically distinct toxins are elaborated by the sporulating, anaerobic gram-positive bacillus C. botulinum. Human poisoning is usually caused by Type A, B, E, or F toxin. Type A and B toxins are highly poisonous proteins ... Exposure to moist heat at 120 C (248 F) for 30 min kills the spores [sEE upthread comments on the persistent hot-oil misconception about this, and why -- MH]. Toxin production can occur at temrperatures as low as 3 C -- i.e., inside a refrigerator -- and does not require strict anaerobic conditions... Home-canned foods are the most common sources, but commercially prepared foods have been implicated in about 10% of outbreaks. Vegetables, fish, fruits, and condiments are the most common vehicles... In recent years, noncanned foods (eg, foil-wrapped baked potatoes, chopped garlic in oil, patty melt sandwiches) have caused restaurant-associated outbreaks... C. botulinum spores are common in the environment...

Always take your food-safety info directly from reliable authoritative sources, not from rules-of-thumb quoted confidently and sincerely on online food fora!!

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...

... Toxin production can occur at temperatures as low as 3 C -- i.e., inside a refrigerator -- ...

- slowly, as I understand it. I extracted my personal rule of thumb above from a long paper that described experimental results over time for different strains / substrates / temperatues.

Always take your food-safety info directly from reliable authoritative sources, not from rules-of-thumb quoted confidently and sincerely on online food fora!!

Amen.


Edited by Blether (log)

QUIET!  People are trying to pontificate.

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Blether, since you added the point about temperature, here's a little more on that complex subject incl. an aspect the health-science sources rarely address for home cooks.

Official advice quoted way upthread certainly favors refrigeration over unrefrigerated storage. (Purely from memory, in the lethal US case Roueché publicized, the spiced mushrooms, after long boiling in wine, were kept under oil for something like ten days in a cool household storage pantry. Incidentally Roueché didn't report the C. bot. spores' source in that case -- might equally have been the mushrooms themselves or one of the spices, such as peppercorns.)

The refrigeration picture is complex both because of multiple C. bot. strains (which the medical sources tell all about) and the variation in refrigerator temps. (which they don't). I've measured some of the latter directly, using the precision recording thermoms. that I use elsewhere with wine storage. Nominal target temp. for US refrigerators is 38F (3.3 C) (for still other reasons). But in practice (a) the target temp. varies somewhat between units and (b) more importantly, it cycles up and down, how much depending on thermal mass enclosed, construction, and especially, how much time the door stays open. I've observed temp. swings to about 60F (15.6 C), down to below freezing (which explained some wilting vegetables. :-(

So the official advice to refrigerate vulnerable foods for a few days and freeze for longer storage [more quoted upthread] isn't and really can't be more quantitatively specific.

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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:

I have GOT to get this book ! :D


"You dont know everything in the world! You just know how to read!" -an ah-hah! moment for 6-yr old Miss O.

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...I have GOT to get this book ! :D

A little more on Berton Roueché, then, for anyone so unlucky as to be unacquainted with his writing! Including info you won't see in standard online sources.

From about the 1950s through the 1980s, Roueché wrote a column in the New Yorker, "Annals of Medicine," reporting real-life cases of rare or tricky disease identifications, often solved by public-health doctors, that came to be called medical detective stories. Many involved foodborne illnesses.

Roueché's name was almost a US household word in his heyday: For literally decades, his original paperback anthologies Eleven Blue Men and The Incurable Wound, and a collection he edited of other medical writing (Curiosities of Medicine), were on every airport or supermarket books kiosk. Later, longer, anthologies included newer material and some, but not all, of the gripping stories in the famous original two books. You've seen some Roueché stories already (not always clearly credited), like the case of the "poison pants" that Arey alluded to earlier, if you've watched much of the celebrated US medical TV series House. (Credit Roueché for at least some of its success.) Possibly his best-known story, "Eleven blue men" (also the first anthology's title), has long been recommended to medical students (in a standard medical text I have) for its case study of a rare foodborne illness, accidental distribution of sodium nitrite mistaken for salt in a cafeteria. Nitrite depleted the victims' blood oxygen temporarily and they turned blue; contrast another of his cases, a man turning bright orange, with a similarly hard to trace but much more benign foodborne cause I won't spoil for you.

The cases are fascinating; Roueché's style is part of it. He was an incisive nonfiction narrator with scholarly attention to background. Thus his leprosy case (opening with a man reading a magazine, smoking a cigarette, and smelling something burning, only to find it was his own skin from the cig. and he hadn't felt it) goes into ancient and religious accounts of the disease, whose victims often were shunned. That is one of the memorable early stories absent from the large later anthology The Medical Detectives, which I have. The original two books (which I sold off for a few cents when graduating from college) becamse so rare and sought that they fetched upwards of $100 when I last checked. And some of their most memorable stories don't seem to've been reprinted much if at all, for whatever reason. Maybe medical obsolescence, or increased cultural sensitivity to certain details. The leprosy case ("A lonely road"), heroin addicts in Harlem carelessly cutting their drug ("A pinch of dust"), and specifically the botulism case I've cited in this thread ("Family reunion") all are missing from the large modern anthology The Medical Detectives.

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Wow! Thank you. I will try to dig up a copy at below the current going price.

I wonder if he was involved in finding the cause of death for 3 hunters, found dead around their morning campfire?

Turns out they'd left the coffee pot out overnight, and in the am, first one up just heated up the leftovers, and all drank. All 4 died - the poisonous salamandar/newt that had crawled into the pot overnight, and the hunters that it poisoned inadvertently.


"You dont know everything in the world! You just know how to read!" -an ah-hah! moment for 6-yr old Miss O.

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And peach are not 'low acid'. They are in the 'acid' category. I don't think they've even been a problem. Who knows where these people get this stuff. I just heard on a newer PBS show that excluding oxygen is all you need to do to prevent spoilage, when it's actually the opposite for botulism. Must have taken a little information about keeping out O2 to prevent mold and such and basic human biology and come to an erroneous conclusion.

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I am a retired microbiologist. Botulism comes from the soil and one ppm of the toxin is lethal. The reason you don't keep a raw plant (basil) immersed in oil even in the refrigerator is that botulism is an anaerobic bacterium. It goes without oxygen and in non acid conditions. Basil leaves and oil are a perfect place for this bacterium to grow.

You can make all the pesto you want and put it in the smaller baby food jars and freeze it. Even if present, the organism can't grow in the freezer. As you have read above, citric acid will acidify the product which has also been heated, so commercial products are safe, but not as tasty.

Remember no acid, no oxygen, is a definite no no, thus all the cautions involving canning green beans. Be safe and freeze your basil and smile all winter long.

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