display | more...
If you decide to make any type of garlic oil, please remember that it can become the cosy home of a bacterium, your best friend clostridium botulinum, a microrganism that produces a deadly toxin called botulin, which in turns produces a very characteristic and dangerous syndrome called botulism. The botulinum likes moist, anaerobic (that is, oxygen free), basic places, just like garlic and peppers in oil.
Even heating the oil does not really cut it, because the botulinum is very hardy. And this is why you should stay away from home-made garlic preserved in oil, or home-made garlic flavored oil. Commercial packers acidify the garlic.

(source: On Food and Cooking: The Science and Lore of the Kitchen by Harold McGee) and a msg from shaogo.