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Fresh Herbs in Olive Oil

We have a nice herb garden on our back deck. A few weeks ago, after a visit to a local restaurant, I decided to put a sprig of fresh rosemary into one of our olive oil bottles to create a flavored oil. I cut a sprig, washed it and dried it off, and inserted into the oil bottle. Within a few days, the flavor had permeated the oil well and it was delicious. Unfortunately, I forgot to keep the oil above the rosemary and the top of the stalk grew mold, so I had to discard all of the oil and thoroughly wash the bottle, which I then just refilled with good oil, no spices. However, I did really like the oil, so before I do it again, is there any secret or warnings other than "don't let the rosemary leaves get exposed to the air above the oil"? Is it going to grow something funky even submerged in the oil? How long should it keep? Would it be better to tightly cork the bottle (it has one of those dispenser spouts now, like a liquor bottle)? Should I dry the rosemary first? Treat it in any way? Any advice would be appreciated.

Yes here's the BIG secret and WARNING, herbs in oil is an especially good way to grow BOTULISM! But here's the easy way to prevent it, either keep the oil refrigerated (and it must be refrigerated immediately, once the bacteria starts to grow the cold only slows it) or add a tablespoon of lemon juice or vinegar per cup of oil.
CMPalmer (author)  Tool Using Animal6 years ago
I'm not disputing you and this is exactly the kind of thing I was looking for, but this raises new questions: Do restaurants just take the risk or do they throw out all of the oil every day or so? How do you add lemon juice or vinegar to oil without it just sitting on top? Are there other preservatives/anti-bacterial agents that can be used? I found another site that said something to the effect of "supposedly you are supposed to refrigerate herbed oils after opening and use them all within a few weeks, but two generations of our family have kept them out on the counter and just keep adding oil to keep everything submerged." Is the person who is saying this just lucky, is this a 0.01% chance of occurring, or what?
> How do you add lemon juice or vinegar to oil without it just sitting on top? . Just shake/stir it. The acid matrices are soluble in oil - that part of the reason they make good household cleaners. . > Is the person who is saying this just lucky, is this a 0.01% chance of occurring, or what? . Yes. Like discovering penicillin, contracting food poisoning takes a bit of serendipity. But if you take chances long enough, you're bound to get bit. . Keeping your eyes (and nose) open, along with modern food handling/prep will keep you pretty safe.
CMPalmer (author)  NachoMahma6 years ago
Being an experimentalist type person... I think I will keep my next attempt refrigerated for consumption, but assume that I want a room-temperature control. What do I look for for contamination? Cloudiness, odor, anything? How would you go about testing for bacterial contamination in a scientific manner (particularly an amateur scientist/Make reader/Instructables sort of DIY way)? Is it detectable at all without really complex tests? I also assume that if I cook with the oil (rather than putting it on a salad (in which case herbed vinegar would be a better and safer choice) or using it as a bread dip), then the safety factor is greater due to heat? For the people who create this kind of stuff as gifts, would you follow home canning procedures (boiled/sterilized bottles, quickly sealed) with instructions to refrigerate after opening? Would wax and/or corks be sufficient? Any tips of doing this (or should you just stick with vinegar)? Thanks for all the comments, BTW. This is what I love about groups like this. I really hate it when you ask questions on specialty forums and the answer is "don't do it unless you are a professional" - where is the fun in that?
I don't worry when something says "don't do it unless you are a professional". I just tell people that I'm a professional amateur. :-)
> I think I will keep my next attempt refrigerated for consumption . That should be safer. May affect the taste. I'd keep my stock refrigerated and decant 1-2 weeks worth to keep at room temp. . Pasturization, as lemonie mentioned for the herbs, would probably help, but I'd be concerned that this may change the taste. Since you cook with it, this may not be a problem. . > What do I look for for contamination? Cloudiness, odor, anything? . I'd be suspicious of _any_ change. Some cloudiness may occur when refrigerated. . I'm guessing it would require some type of clean-room. Probably outside the scope of most DIYers. You may be able to find a field test kit - I'm visualizing something like a swimming pool pH kit. . > would you follow home canning procedures (boiled/sterilized bottles, quickly sealed) with instructions to refrigerate after opening . I would think that would be wise with any food. . . Have you looked on olive oil producer/distributor web sites? Wouldn't be at all surprised to find a few sites dedicated to olive oil lovers. You might get a "pros only" answer, but who knows - I bet olive oil ppl are just as nice as DIYers. Sounds like all of us here are just making (educated) guesses.
knower CMPalmer4 years ago
Not sure if this is possible : -
Botulism spores are killed when canned food is boiled for 1 min at 100 C or the food is pressure cooked for 30mins. What I would suggest is to pressure cook your infusion and make sure the temperature is above 100 C  for 30 mins.
I'd say it's a low probability thing, but.. The restaurants I have three ideas. they just take the chance, the oils is a commercial product that's been pasteurized, or the oil has been acidified by the addition of citric acid (which can be made to dissolve in oil). Way back when my girlfriend and I did things like this, we'd just dip the herbs into the lemon juice before placing in the oil, yeah, it eventually separates.
I've never done it, but I've heard of washing your herbs in a really diluted bleach solution, then rinsing them hot. Another easy way to kill most of the bacteria on them would be to freeze them first (most herbs take pretty well to freezing.) I've never tried either in this application, though, so I can't guarantee any results _
Not bleach, no. A blanch, or sulphite treatment perhaps. Drying, or heating should be just fine.

Worth noting that restaurants will most likely shift oil more quickly, hence the bottles empty before anything goes off(?)

See here also
http://www.google.co.uk/search?hl=en&q=rosemary+olive+oil+make&btnG=Google+Search&meta=

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NachoMahma6 years ago
. It sounds to me that if you can keep the herbs submerged, your dispenser spout should be OK. Sealing might help if a bottle lasts more than a few weeks, but air gets sucked in every time you pour some out. . Sterilization, as technoplastique and lemonie describe (I'd guess that the dilute bleach would be easiest and should be very effective), should help, but may not be necessary if you can keep the spices out of the air. I'm guessing it's airborne, not something on the herbs.
lemonie6 years ago
Hmm, the thought of heating the oil springs to mind. You wouldn't want to fry the herbs, but ~100oC for a few minutes would sterilise.
Dried would reduce the moisture content preventing mould growth (if dessicated enough).
To keep submerged, you could bend your sprigs in two and push into the bottle with the bend lowermost. In this way the herbs could self-wedge below the surface (might be difficult to get them out though)

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