Garlic in Olive Oil Safety

[Lisa Shock]

At the 1st restaurant I cooked in the chef instructed us to pass a container full of garlic cloves through a meat grinder into a bucket and cover the "crushed" garlic with olive oil.  We cooked with this stuff and the service staff placed little ramekins of it on the tables for the customers to dip their bread in.  Personally, I wasn't down with it, thought it was quite disrespectful to the product to ram it through a meat grinder (I didn't work very long at that restaurant).

I choose to sous-vide my garlic with olive oil and salt.  The final product is a perfectly infused oil with very sweet garlic.

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SV garlic with olive oil and salt at what temp. and how long?

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60F for 6 hours; I also place a few sprigs of thyme in there as well.

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That's a pretty good recipe for culturing botulism, and a big reason why health departments in certain cities are not approving sous-vide equipment in restaurants. You need acidity or higher temperatures or exposure to air to kill the spores. Please note that some temps given in the thread are C not F.

60°F in a vacuum without an acid is botulism's ideal environment.

[andiesenji]

60 Celsius is not hot enough either (140 F.)

That too is far below the safe zone of 240 degrees F.

[MaxH]

I'm a great fan of garlic, and garlic cooked in oil -- but surprised to learn that some professionals don't know about this anaerobic pathogen problem. It's a famous public-health concern, it's in online food-safety information from US and other gov't agencies, WHO, etc. With C. botulinum, as most of you know, the hazard is complicated because it forms in three stages (spores to viable bacteria to toxin, each with very different characteristics). Even some of the incidental science, apparently, isn't fully intuitive. Andiesenji, not to single you out but there's an insidious error here:

... Olive oil boils at 375 degrees F., in the oven at 275 F., it will reach 250 degrees after one hour, fifteen minutes ...

Email or PM me if you need more background on the following or if it doesn't make sense to you -- I assure you it's well supported: Under no circumstances can you reliably raise temperature of most foodstuffs to 250 deg F (121 C) at atmospheric pressure. That's because as long as water remains, it very effectively limits microscopic local temperature to 212 F (100 C) regardless of convection medium (oven air, oil, etc.). In fact, water's very good at that, due not only to its boiling point and heat capacity, but also its Lvap (latent heat of vaporization) which absorbs energy before phase change can occur (liquid to gas). Water's Lvap is relatively high, over 2 Megajoules (millions of watt-seconds) per kg (incidentally the thermodynamic reason a "watched pot never boils!") Even foodstuffs that look dessicated typically contain significant water unless kept in vaccuum. Under steam pressure though, the BP and Lvap effect move to higher temperatures and the entirety of the food easily reaches 250 F.

Cooking in a superheated medium like oil eventually raises surface temp. (that's why fried potatoes brown) and this could (I assume) helpfully kill many surface C. bot spores. But still not reliably, since a large thermodynamic "heat sink" from immediately adjacent H20 works to pull down even the surface temperatures, while the evolving gas (steam) surrounding the surface insulates it partially from the oil. Good luck in avoiding food poisoning so far does not guarantee it won't happen later. Incidentally, C. bot growth does not require complete oxygen exclusion, and one or two of the four important strains grow down to 3 deg C (37 F) (at or below many home refrigerator temps.) acc. to published data (other strains grow down to 8 C). Refrigeration does slow any bacterial growth, so keeping food cool and consuming reasonably soon is a safety measure.

This and related issues in closely related current discussion here under "Food on the Internet."

[wannabechef]

I have a slightly unrelated question but this seems as good a place to bring it up. I once made a pizza recipe a few years ago that had the most simple sauce. I was so skeptical but it ended up being incredible. Basically, it was just raw tomatoes in a food processor, with some salt. Then take it out and put in 2 or 3 raw cloves of garlic (peeled but not crushed or chopped), give it a stir, and let it sit for an hour. Done.

When I first read the recipe I thought it was ridiculous. What's the point of putting in that garlic if you're not going to chop it or even cook it? But I couldn't believe it, somehow that garlic totally infused the tomatoes with an amazing garlic taste. When the pizza cooked with this sauce it was really incredible. Since the sauce was uncooked it had an amazing freshness to it and the garlic really came through as well.

Now to bring it back around - does anyone have an idea as to chemically how the garlic flavor made it into the sauce? I always thought you had to use oil, saute, etc etc to get the taste out. Is it some kind of reaction with the acidity of the tomatoes?

Thanks!

~WBC

[andiesenji]

The chemicals in garlic that produce the flavors and aromas are volatile enough to cross the barrier of the fairly permeable peel and acid will definitely speed up the process and will actually exchange molecules.

You can try a very simple experiment, simply put a peeled clove of garlic in a little dish of vinegar and allow it to "steep" for an hour.

The vinegar will have a distinct garlic flavor and the garlic, which you can wash in clear water, then dry, will have begun to be pickled.

[MaxH]

...raw tomatoes in a food processor, with some salt. Then take it out and put in 2 or 3 raw cloves of garlic (peeled but not crushed or chopped), give it a stir, and let it sit for an hour. Done.  ...does anyone have an idea as to chemically how the garlic flavor made it into the sauce? I always thought you had to use oil, saute, etc etc to get the taste out.

Did you by any chance handle the garlic cloves after steeping in the sauce, and feel the texture of their skin?

I ask because (though it's a new one to me too) I see no reason flavor can't diffuse out through the thin membrane of the peeled garlic clove's skin, especially if the tomato puree tends to soften it. Tomatoes are made up of all kinds of stuff, much of it organic -- fats, proteins, water, sugars, organic acids. Many of those components can dissolve oil-based flavorings, so there's a reservoir of mixed solvents just outside the garlic clove, and they may also serve to soften up the garlic clove's membrane surface. (Chemical components diffuse through membranes all the time in other situations.)

[Vision]

Well after one week of the in and out of the fridge treatment, the oil was infused, smelled good, but did not have the robust taste. Will leave it in the fridge for a month and check back.

[Lisa Shock]

Well after one week of the in and out of the fridge treatment, the oil was infused, smelled good, but did not have the robust taste. Will leave it in the fridge for a month and check back.

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What sort of "treatment"? Did you acidulate the garlic? Pressure cook it to 250°F for more than five minutes?

Once again, I'll point out that the standard recommendation is to make and use infused oils in the same day, no longer.

And, that the restaurant which you are attempting to emulate would be promptly shut down if the health department in most US municipalities discovered them making and/or serving garlic oil.

[dougal]

... Will leave it in the fridge for a month and check back.

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Once again, I'll point out that the standard recommendation is to make and use infused oils in the same day, no longer.

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Ummm.

I do think a month is a bit long without proper (canning temperature or acid) treatment.

Its a fairly small risk, but of a deadly serious consequence. Better not.

The official British advice for domestic kitchens is that while same day use is safest, nevertheless, its OK to hold it for a week in the refrigerator. For example --

Even though recipes for flavoured oils can be found in cookery books, magazines and websites, these might not have considered the risk of botulism. So if you would like to make your own flavoured oil, the safest option is to make a small quantity and use it on the day you have made it. If you have some oil left over, put it in the fridge straight away and use it within a week. Some oils can go cloudy or become solid in the fridge, but if this happens don't be tempted to leave it at room temperature, because this might not be safe.

My emphasis.

Original located at at http://www.eatwell.gov.uk/asksam/keepingfo...paring/#A279852

[Vision]

The organisms are characterized by their straight, slightly curved, Gram-positive, motile, anaerobic rods, which produce heat-resistant spores. The spores become activated in a low acid (less than 4.6), anaerobic environment with temperatures ranging from 40°F to 120°F,

http://edis.ifas.ufl.edu/FS104

[MaxH]

dougal's point on refrigerated storage time accords with what I saw when researching official advisories on the subject of anaerobic (e.g., in oil) storage of foods not processed to prevent anaerobic bacteria. A "Few days" time frame is recurrent in the advisories. Even if activated, C. bot bacteria take time to grow and develop toxin. And not every bit of food comes with the spores on it, or we might see shocking headlines about people following suggestions like those below, posted on another popular food site. As dougal said, it's a small risk of a deadly serious consequence.

i always have some garlic confit on hand ... and think it is fabulous! I use a slow cooker to make it about once every two months

Another posting offered a simple recipe for making confit from frozen ducks: season for a day, and slow cook in oil for 12 hours. Nothing there (or in the surrounding thread) about type of seasoning, or its relation to anaerobic hazards. The writer characterized the recipe as "dead easy."

I posted a little more background on eG's sous-vide thread. Very recently, US Food and Drug Administration completely revised its Web site (voiding many useful links). A relevant resource is its Center for Food Safety and Applied Nutrition (CFSAN), formerly http://www.cfsan.fda.gov -- that link at least still does something, it forwards to a new general food page http://www.fda.gov/Food/default.htm . Every few years, CFSAN has released the comprehensive US "Food Code" (in pdf format) aimed mainly at businesses, with information on practical situations where food poisoning is an issue. Here is a new index of food guidance documents. FDA corresponds to the Health Ministry in many coutries. International bodies such as WHO also have guidance documents about botulism prevention; Google finds them.

In a parallel thread here about a questionable New York Times recipe, which I linked a few postings ago, is more on modern confits, the unpublicized risks they raise, and the skepticism that sometimes greets raising this issue.

[MaxH]

...spores become activated in a low acid (less than 4.6), anaerobic environment with temperatures ranging from 40°F to 120°F

Vision, I've previously posted (here and elsewhere) upshots of more precise, authoritative sources such as the US FDA:

Certain strains of C. botulinum ... can grow and produce toxin at temperatures as low as 3.3°C ... Other strains of C. botulinum (type A and proteolytic types B and F) can grow and produce toxin at temperatures slightly above 10°.

3.3° C is just under 38° F, the traditional, nominal US refrigerator temperature, but not all refrigerators run (or run consistently) at that temp. Advisories related to that above characterize "refrigerator temperatures" as 0°-8° C (32°-46.4° F). Refrigeration provides no assurance of safety. I urge people to be more careful about defending practices that happen to be familiar. (Another example surfaced in the parallel thread.) Compare the consequences of being a little too careful vs. a little too careless. When I learned about botulism (around the time of the Bon-Vivant soup scandal, which ruined that firm), mortality rate was one-third. It has gone down a little but it's still grave.

Also Vision, I'm sure you (or your source) meant to write for a low-acid environment "above 4.6." The lower that number, the higher the acidity. (pH is a log scale of ion concentration, neutral water is pH 7. Long ago I measured fresh lemon juice at about 2.0, which approaches some concentrated mineral acids, by the way.)

[dougal]

Time and temperature are important.

And interdependent.

We all know that fridges don't preserve stuff for ever.

They just slow down the biological processes.

And they slow down c. botulinum too.

Yes, some strains can grow in some fridges. But massively more slowly than at room temperature, or (fastest of all), at 'warm food' temperature.

So basically, the cooler you keep it, the longer you can keep it.

But if 7 hours at room temperature is OK ("same day" use), and one week in the fridge is also OK, its important to understand that does NOT mean that 7 hours at room temperature followed by a week in the fridge is equally OK.

On those numbers, you'd be better to say: 'for every hour at room temperature, cut a day off its fridge life' - and don't forget to allow for the time after it comes out of the fridge!

Hence you get to the general advice that "a few hours at room temperature plus a few days in the fridge" is pretty safe.

There's no point in exploring how often you can dodge the bullets.

Even if nanny is worried about very rare risks - because of their serious consequences - and the official advice is so cautious that it keeps the risk probability down below other risks that we accept without a care, nanny really does know best.

So keep it in the fridge and make fresh at least each week - using a clean container, don't just refill it.

And of course, if stricter local ordinances apply to you - obey the law.

[dougal]

Hi everyone, first post here. I've worked in a few restaurants ...

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Here in Phoenix, it's a violation of the health code to make or serve garlic oil, regardless of how it is handled.

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... the restaurant which you are attempting to emulate would be promptly shut down if the health department in most US municipalities discovered them ...

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I hope that is clear enough.

Edited July 21, 2009 by dougal (log)

[BadRabbit]

I'm reviewing a cookbook on pickling\oil preserving for a publisher and I've noticed there are several recipes that I would say have questionable safety practices. 

 

In particular, one oil combines fresh mashed garlic and Herbs d' Provence with olive oil then lets them sit for a week before straining the oil. There is absolutely no mention of applying heat or refrigerating at any time. Am I wrong that there is a potential for botulism here? Mashed garlic in an anaerobic environment for a week at room temp (plus longer for the strained oil) seems dangerous but perhaps I'm missing something.

 

Just wanted to check before I sent up a red flag.

[daveb]

I don't like it.  Can't point to any science but garlic and botulism go together like white on rice.

 

Same recipe, used fresh would be fine.  Roasted for an hour or so, then refrigerated would be fine.  PC to a garlic confit then refrigerated would be fine.  

[Norm Matthews]

There is a problem with that recipe.  If you combine fresh garlic and oil without heat or refrigeration, I think you should use it the same day. 

[gfweb]

Agree with above.

 

And there is an issue with how long it is safe even after being refrigerated.

 

This is the kind of thing that one could get away with for years and years before the wrong bacteria gets to growing.

[gfweb]

here you go

 

https://theolivepress.com/news-blog/be-aware-of-the-risks-of-botulism-with-homemade-garlic-infused-oil#.Vh0zBCtmpKM

[Smithy]

I agree that there's a problem. For additional discussion about this, check out this topic:

Botulism concerns re infused oils and confit

[BadRabbit]

This book is a mess. It's got zero pages on safety and there is a specific line at the beginning of the book that says to feel free to adjust recipes to your own taste. Given that some people might be looking for less sour and reduce or eliminate the vinegar in some recipes, that's a potential deadly piece of advice. 

[AlaMoi]

"I'm reviewing a cookbook on pickling\oil preserving for a publisher...."

 

considering some of the questions and advice I've seen published on cooking websites, can't say I'm surprised in the least.

time to time you see "professional" ala ChefTalk come out with stuff that will stand your bacteria on end - and these are people who purport to cook in restaurants for a living.

 

some people don't know better, never knew better, can be bothered to learn better, then they write a cookbook.....

 

"......that's a potential deadly piece of advice"  when things get taken out of context, they can go wonkers real fast.  if this is a chef from a starred restaurant talking about preparing a high end dressing for their GMO free organic washed in glacier water baby greens grown on the east slope but only above 15,000 ft yadda yadda as they be so prone to prattle on about.... the "recipe" is fine.  when a ghost takes the recipe at with no knowledge of anything other than "spelt check" then thinks the prep can be put in the pantry for use until gone, well, that raises some hairs.

[gfweb]

Not knowing what you don't know is always dangerous; especially with uncommon events.

 

Lets say the risk of botulism from garlic oil is 1 in 500 (I'm making that up). You could make many many batches and feel more confident with each one before the lethal one was made.

[Lisa Shock]

Random positive reinforcement is a powerful motivator. We also become comfortable with routines, especially those we observe while growing up. That doesn't make these activities safe, and doesn't mean they produce foods with optimal nutrition.  (for example, you probably won't become sick immediately from improperly stored, mildly rancid fats, but, they are fairly likely encourage the development of certain types of cancers over time)  This article by McGee on Ruhlman's method of storing his homemade stock at room temperature is very enlightening.

 

The publisher needs to know that they should be having someone educated in nutrition, food safety and sanitation checking their cookbooks.

 

Roasted garlic infused in oil then refrigerated is not always 'ok'. As long as some moisture remains in the garlic, when roasting, those parts of the vegetable have not exceeded boiling water temperature -if they had, the water would have become steam and dissipated into the oven. To kill botulism, you need to hit 250°F for ten minutes -something generally done by pressure frying, or making confit in a carefully monitored pressure cooker.

[BadRabbit]

I review a lot of cookbooks and have reviewed several on preserving\pickling. I have never seen one that avoided the food safety issue completely. This one does mention water bath canning but just as a method and doesn't even mention why you are doing it or that it is only safe for use in sufficiently acidic preparations. 

 

I've already sent an email informing the publisher that I think the book is potentially dangerous and seriously needs to be reviewed by a food safety expert before publishing. The worst part is that the preface of the book says that it's a great introduction to pickling which means they are marketing it to people who almost certainly don't understand the implications.