He mentions that you need to use the oil right away, but I found that if you follow this method, you can preserve the flavor of the oil for quite some time.
1 bottle good cold pressed olive oil
a few sprigs of rosemary
Pour the oil into a cast iron skillet. Heat the oil on low heat just until the oil starts to heat up. Add the rosemary sprigs. You are infusing, not frying the rosemary sprigs, so they should retain their color somewhat, and not be completely brown or charred.
After a few minutes on low heat, shut the heat off and let the oil cool to room temperature. I think this also helps impart flavor onto the oil.
Remove and discard the rosemary and pour the oil into a glass jar or empty wine bottle. Seal with a cork.
I wanted to keep the rosemary in the bottle to see if that will help improve the flavor, but I did not want the rosemary sprig to be caught in the bottle. So, i tied some cooking string to the end of the sprig and shoved the rosemary into the bottle, with the string hanging out over the lip of the bottle for easy removal. I think it definitely helps improve the flavor!
