I bought vacuum packed green and black olives in brine. I drained them, seasoned with garlic, oregano, and dried chili. I put them in sterilized mason jars, topped with olive oil, and sealed the jars. Can i keep them over winter?
No. You run the risk of botulism by creating an anaerobic (oxygen free) environment. It is possible that the garlic, chili and herbs could be the source of the spores that potentially produce the toxin. Sterilization of the jars is irrelevant. You can refrigerate and use the olives over the short term (4 days) but storage at room temperature is potentially problematic. For longer storage, you could freeze. Frozen, this would be safe for several months (though freeze/thaw could potentially impact the texture of your olives).