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I have some basil from my garden that I would like to infuse with olive oil to flavor it. I was going to pack the jar with the herbs and then pour the oil over it, keep it in a jar for about a week and then strain and store the oil for cooking. Are there any issues I should be aware of?

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4 Answers

See this article from Colorado University Safe Food. The goal is to prevent growth of the botulism pathogen. Here are their key points:

  • Wash all soil-contaminated produce before adding it to an oil infusion,
  • Add an acidifying agent such as lemon juice or vinegar to the recipe at the rate of one tablespoon per cup of oil,
  • Keep oil infusions refrigerated in order to retard the growth of any microbes,
  • Discard infusions after one week, or sooner if apparent cloudiness, gas bubbles, or foul odor develop and,
  • When in doubt, throw it out.

Sorry the source article is not formatted prettily, but I was looking for something more authoritative than about.com or ehow.com.

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They mention cloudiness, gas bubbles and foul odour. To my knowledge you can never know if food is contaminated with C. botulinum. "The bacteria and toxin that cause botulism are invisible to the naked eye and do not change the colour, odour or taste of food." Food Safety Tips for Home Canning – Health Canada –  citizen Jan 3 '13 at 3:27
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@citizen That is true. I don't think the warning about the visible symptoms was targeted at botulism, but at other types of spoilage. Nonetheless, the message from all sources to the orginal question is: if you do this at all, do it with great care, and don't hold the product for a long time. –  SAJ14SAJ Jan 3 '13 at 3:30
    
@citizen The acidifying agent is to get the pH low enough to prevent botulism growth, especially in combination with refrigeration. –  derobert Jan 3 '13 at 15:08
    
@derobert: Yes, but you can never determine for yourself by looking at the oil if there is a risk of botulism. And that they mention cloudiness is even more weird when they recommend storing it in the refrigerator – the fats will partially set because of the temperature and (harmless) cloudiness will appear. –  citizen Jan 3 '13 at 15:34
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@citizen indeed, you can't look at it to determine botulism risk. That's what the acid & refrigeration is for, to eliminate it. But there are pathogens other than bacteria, as well as spoilage bacteria. They're saying "it should be safe for a week if prepared like this, but if you notice signs of spoilage, throw it out." –  derobert Jan 3 '13 at 15:49
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I've had good luck with infusing olive oil, but I use a significantly different method:

  1. Blanche and shock the basil. (dip in boiling water for a few seconds, then in ice water).
  2. Put the basil into a pot, and cover with olive oil.
  3. Warm the olive oil, and leave it warm on the stove for a while (maybe 60 minutes)
  4. Strain the oil, and put in jars.
  5. Store the jars in the fridge.

It might take me 6 months to use it all up depending on how much I made; I don't know what the recommended safe storage time is for it, but I keep good practices in making sure that it's well sealed, kept cold, and that I never allow a contaminated utensil into the oil. I also tend to use it for applications that get re-cooked (eg, making croutons) as it gets older, vs. just using it to flavor a parsley-based pesto.

update : right, so I didn't spell out specifically why this is better -- the blanching helps to kill any bacteria (although not spores) on the basil as well as breaking cell walls so that the infusion takes less time. The warm infusion means that it spends less time infusing so that anaerobic bacteria doesn't have as much of a chance to grow. Storing the oil in the fridge further inhibits bacteria growth.

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I've heard of similar techniques for making hot-pepper oils, though they usually call for adding the peppers to the oil then heating the oil on the stove to whatever temperature you need to kill botulin bacteria (it's rather hot, as I recall) and leaving it there for an hour I think. I'm pretty sure I've seen answers on this site explaining the process in more detail. Also found this link: ext.colostate.edu/pubs/foodnut/09340.html –  FrustratedWithFormsDesigner Jan 3 '13 at 16:08
    
Its the hold time of six months that forced me to downvote for safety--take that out, and I am happy to remove the downvote. After all, just because the scary dog hasn't bitten you yet doesn't mean it won't. We have to be very conservative on safety issue recommendations IMO. –  SAJ14SAJ Jan 3 '13 at 16:44
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National Center for Home Food Preservation

How do I can oil with herbs? Can I can pesto?

Herbs and oils are both low-acid and together could support the growth of the disease-causing Clostridium botulinum bacteria. Oils may be flavored with herbs if they are made up for fresh use, stored in the refrigerator and used within 2 to 3 days. There are no canning recommendations. Fresh herbs must be washed well and dried completely before storing in the oil. The very best sanitation and personal hygiene practices must be used. Pesto is an uncooked seasoning mixture of herbs, usually including fresh basil, and some oil. It may be frozen for long term storage; there are no home canning recommendations.

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Just a couple of points in addition to those already mentioned:

  1. Make sure you wash and dry your basil leaves before infusing.

  2. Make sure you sterilize your container by scalding or immersing in boiling water.

  3. Once made, keep in the fridge.

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