Not only does olive oil have a shelf life, but adding aromatics like fresh herbs or garlic to a bottle of olive oil can result in an unintended outcome: Clostridium botulinum, the microorganism that causes botulism by producing a dangerous toxin when provided with an environment in which oxygen is absent, can cause symptoms of a food borne illness that may result in death.
It is the same toxin that we have been warned about for years that can be present in foods that are home canned and the reason we are warned also about the dangers of eating foods from dented, swollen and rusty cans. One way to have both the flavor of the herbs and add to the longevity of the oil without the fear of food borne illness is to freeze it.
Olive oil, unlike water that has a consistent freezing point of 32 degrees Fahrenheit, will freeze, but at different temperatures depending on the type of olive oil. This is due to the chemical complexity of olive oil, with each component having its own freezing point.
Experimentation and experience has shown that at 10 degrees Fahrenheit more or less, olive oil will freeze rock solid. Since the temperature of a modern day freezer is usually set to around ‑3 degrees Fahrenheit, placing it in your freezer will ensure that the oil will freeze solid. Furthermore, neither freezing nor thawing the oil does any harm to the taste or cooking qualities of the oil.
Freezing olive oil in ice cube trays is an easy and safe way to prolong the life of the oil and portion out fresh herb flavored, frozen cubes as needed. Any fresh herbs, garlic and even citrus zest can be used.
Cut or mince the aromatic before mixing it into the oil. Warm the oil until the aroma from the herbs is strong then cool rapidly. Pour the liquid gold into an ice cube tray and place it in your freezer. When you are ready to use the olive oil, remove as many cubes as necessary and let them thaw slowly in a pan on low heat.
Adding herbs and freezing gives you olive oil flavored safely, to use as whenever you need it.