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I am infusing olive oil with truffles. How can I do it safely? Heating the oil destroys the truffle smell and pickling it is a sure way to do the same. Are there any other methods? Perhaps some type of filter that will eliminate the particulates?

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2 Answers 2

Edit This answer assumes that you want a shelf-stable oil. If you are going to use up the oil immediately (or within 3 days and refrigerate), methods like the pressure charging from moscafj's answer don't pose a safety problem.

Simply, you can't. I am not sure how industrial oils are made, maybe they are irradiated or simply made under sanitized conditions and at the end microbiologically checked to ensure that a given batch isn't contaminated, but it isn't something you can do at home.

There are no methods accessible to home cooks to prevent botulinum in low-acid foods. Heat won't work, as botulinum bacteria don't just live like any other bacteria, they also form spores which will survive temperatures which would have incinerated other species with a single form. You can never reach these temperatures in a watery medium, e.g. in canning purees, in industry it is done in canners with much higher pressure than home pressure canners. In oil, you could theoretically reach the temperatures as you are not limited by the water's boiilng point, but as you pointed out, the flavor will change a lot. In the worst case, you will have to bring the oil to above smoking point to ensure safety.

Filters won't work, as any filters small enough to hold back bacteria are too tight to permit something as viscous as oil to flow through, and botulism toxin isn't "particulate matter", it is dissolved in the food.

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Truffle oil have nothing to do with truffles, it is made by a synthetic aroma component of truffles. –  Stefan Jan 30 '14 at 14:56
@rumtscho: Gamma irradiation is incompletely effective against botulism toxin: cdc.gov/biosafety/publications/bmbl5/BMBL5_appendixI.pdf (see table 1) Looks like pre-autoclaving your truffles is the way to go. That MIGHT be faked up with a pressure cooker. –  Wayfaring Stranger Jan 30 '14 at 14:59
OK, I thought it was obviuos that my first sentence was pure speculation. The important part was to point out that, whatever they do, you can't do it at home. Thank you both @stefan and Wayfaring for giving the details of how it is actually done, they are interesting. –  rumtscho Jan 30 '14 at 15:00
@rumtscho: sure, your speculation just made me curious. –  Wayfaring Stranger Jan 30 '14 at 15:23
@Robert: I don't know where you got 20 from, there's an average of 145 cases of botulism in the USA every year. Part of the reason that number is low is that most people do not attempt home canning; and most of those who do, use high-acid foods like tomatoes. C.botulinum is one of thousands of anaerobes; you can probably get a dozen more examples from Wikipedia, including facultative anaerobes like Listeria, which affects 1600 people in the USA every year all by itself. All types combined easily affect tens or hundreds of thousands. –  Aaronut Mar 2 '14 at 13:24

Dave Arnold developed an effective way to infuse oil with aromatics that are heat sensitive. To employ it, you need an ISI or other brand whipper. Here is an example: https://www.starchefs.com/product_education/iSi/whipper/html/recipe-lemon-infused-extra-virgin-olive-oil-dave-arnold.shtml

I've had great success with the technique and see no reason why you couldn't use it with truffles. From a brief google search, it looks like you should refrigerate this oil and use it within a month to avoid any risk from botulism.

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That example is of using lemon, which is acidic. The doesn't seem like an equivalent of the problem faced with other flavors. –  Caleb Mar 2 '14 at 8:04
It is an intriguing infusion method though. Low End- High End- Chargers It's worth experimenting. Refrigerate and use quickly. –  Jolenealaska Mar 2 '14 at 10:49
@Caleb: No, it uses lemon zest, which is pretty much inert. It's like using dried spices; you can even buy it as a shelf-stable product. You can't acidify oil; the whole concept of an acid or pH only makes sense in aqueous (water) solutions. –  Aaronut Mar 2 '14 at 13:28
@Caleb the original question asked how to infuse an aromatic ingredient in olive oil. Acid has nothing to do with it. One could heat the lemon zest in the olive oil to infuse it, but that would destroy the aromatic nature of the olive oil. While the original poster was concerned about losing the aroma of the truffle by heating, I believe the ISI method would accomplish his goal. Safety is a secondary issue, but one would simply need to refrigerate and use in the near-term. –  moscafj Mar 2 '14 at 16:34

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