Infusing olive oil with herbs

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.

Flavored oils are a low-acid anaerobic (no air) environment. Herbs add a moisture source and can allow botulism bacteria to grow. Even if herbs are removed from the oil after infusing for a brief period, they may have already contaminated the remaining oil with botulism toxin and/or allow small pieces of herbs to remain where the bacteria can grow. Commercial herbed oils rely on acidification to prevent spoilage, since botulism bacteria can't grow in a sufficiently acidic environment. Because the temperatures required to kill the bacteria spores (around 250F) will degrade the oil and/or herbs, acidification is the only practical way to ensure safety for long-term storage while maintaining quality and flavor.

As SAJ14SAJ's answer points out, a brief imprecise acidification step is sufficient to maintain quality of oil for a short time at cool temperatures. But even refrigerator temperatures are not sufficiently low to completely stop botulism bacteria from growing over long periods. Most food safety sources recommend that homemade herbed oils -- acidified or not -- be stored in the refrigerator and used within 2-4 days.

For commercial herb oil stored at room temperature, the processing depends on consistent procedures that can be tested and verified in a laboratory to ensure sufficient acidity. However, until recently, no consumer guidelines had been thoroughly tested to allow home acidification for long-term storage.

Following research conducted at the University of Idaho and published in 2014 in the journal Food Protection Trends, there are now consumer guidelines to process certain herbs and garlic safely through acidification before adding to oil.

Here is a summary of the procedure. Be sure to read the guidelines link thoroughly and to follow the instructions precisely. Note that the following procedure has ONLY been tested so far with basil, oregano, and rosemary, as well as (finely chopped) garlic. Other herbs may require different amounts of acidity during processing to achieve safe results.

1. Make a 3% solution of citric acid by combining 1 level Tablespoon of granular citric acid with 2 cups of water. (Note that other acids, lemon juice, vinegars, etc. have NOT been verified and tested for safe home use in this step.)

2. Combine fresh herbs with the 3% citric acid solution in a ratio of 1 part herb to 10 parts of the acid solution by weight. Weighing is recommended here, since the volume measurement of herbs is imprecise.

3. Place a weight on top of the herbs to ensure they are completely submerged in the solution.

4. Let herbs soak in the acid for 24 hours. (This is a minimum to ensure safety; a longer soak may degrade the flavor.)

5. Remove the acidified herbs, drain, and pat dry. Combine the acidified herbs with oil, and infuse. A ratio of 1 part herbs to 10 parts oil by weight is recommended, but the ratio can be varied from this to achieve appropriate flavor.

6. While the procedure recommends removing the herbs once appropriate flavor has been achieved (generally in 1 to 10 days), there is no food safety risk if the herbs are kept in the oil for longer.

7. Store in a clean, food-grade bottle in a cool place protected from light. The guidelines note that there are no food safety concerns about storing these oils at room temperature, though they recommend storing in the refrigerator or freezer to maintain flavor and quality for a longer period.

IMPORTANT DISCLAIMER: Food preservation is not to be taken lightly, particularly in situations that are known risks for botulism. People who are familiar with home canning recipes already know that one should only use approved recipes and procedures that have been thoroughly tested; this procedure is no exception. Botulism risks are generally low, but the consequences of deviating can be severe.

If you are not willing to go through this detailed procedure (or another one from an approved food safety and preservation organization), be sure to store any herbed oils in the refrigerator and use within 2-4 days or freeze.

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.

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.

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.

i have read in this artile that coconut oil medium chain ftty acids kill certain bacteria including botulism, although i would like more sources to confirm this so that i could make my garlic oil without worries

page 72 https://books.google.com.mx/books?id=tSGmnBeRpLkC&pg=PA72&lpg=PA72&dq=coconut+oil+botulism&source=bl&ots=HceH2FTblP&sig=7hkScj7lQabEoe9ZUSZD6jZqMPI&hl=es&sa=X&ei=lxsqVd3bMsKusAWN1YGwAw&ved=0CE4Q6AEwBg#v=onepage&q=coconut%20oil%20botulism&f=false