After they are canned, that is, from the store, or wherever.
An interesting history I was reading of how black olives came to be put in cans instead of glass jars (after several people died). A documentary says what caused this is the most toxic substance on earth! 
The thing is, if they are the perfect medium for botulism to grow in, and canned food is occasionally contaminated this way, then chances are that olives would be that can. So, I’ve read about this and C. botulinum, where it says that boiling the food for several minutes will detoxify the bacteria in there. Of course it is supposed to be done during the canning process, but nothing is perfect (except the bacteria is like a perfect storm that can withstand almost any condition, and sometimes just the toxin is removed by heat, so it could still develop in there, as a spore, however uncommon this may be—you know, there’s occasional news of foodbourne illnesses and recalls, but only after someone gets sick or worse). As far as what is in glass jars, they say that pickles are sufficiently acidic to prevent growth, even if the spores are present, and the same goes for green olives, which are not ripe.
Okay then, I tried boiling some olives out of a can for 10 minutes (as one article suggested for safety). They stayed about the same in look and feel, but it removed the greasiness and most of the flavor. The article on botulism says food might need to be boiled just over 5 minutes, which could retain more flavor there. I was also thinking that boiling in olive oil should help me avoid ruining them (maybe next time).
Yes, this was better. The olive oil kept the olives from losing flavor, in five minutes of frying, versus boiling in water for five. The heat affects them more in oil, as they shrink or shrivel a bit, but the flavor is still there (in more of a prepared way), so I guess that’s the best of both worlds. I’ll just reuse the oil to make the most of it.
Might want to boil, no, deep fry the black olives… yeah that’s it (or they’d be about the same baked). I tried this with canned artichoke hearts too, since I had a pot full of oil. Well those are good, like any fried veggie I guess, and they also come in either glass jars or cans, but I’m not sure if it has to do with them being marinated or not. Anyhow, maybe I’ve developed a taste for paranoia (yet I needed a source of fat, so it isn’t totally redundant).
You never know. A book on processing heat preserved foods says the moist vegetables, like onions, would not get hot enough while frying to prevent botulism in canning, and that around 70% percent of outbreaks may be due to home canning. So I’d say some percentage of the rest would include stuff off the shelf (besides foodservice, and catering, etc). Oh yeah, currently in the news there are examples of each source of an outbreak going on somewhere. What a coincidence! It isn’t entirely a thing of the past then.
One of those articles confirms my suspicion in general:
A book on Producing Table Olives mentions that green olives have been known to cause botulism in multiple persons too, when not refrigerated, because the acid levels in the jar were not sufficient to prevent it. For that matter, I’ve read that any fruit or vegetable with moisture content greater than the oil it is covered in (e.g., fresh olives in oil) should be stored below 39°F (4°C), and used within two weeks, as well as not left unrefrigerated for more than two hours. As a precaution, the acidity of the jar may be tested with a chemical strip (and should be pH 4.6 or lower), especially if stored otherwise, or not cooked afterwards.
