Why green olives come in jars, but black ones come in cans
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"Freda perfected the recipe, sold her olives locally, then went East to open up new markets. She scored her first hit in Philadelphia.
Eventually, she had a national business, requiring new orchards, and factories. She kept going back to the University of California for more tips—including packaging.
"When she first went to Philadelphia, she had them in kegs and barrels—just sort of loosely covered, you know," Taylor says. "Not sealed."
"Then, glass jars. Because they don’t spill?
"Yes, and they’re very pretty," Taylor says. "And gradually they developed a technique of sealing the jars effectively. And with that came trouble."
You seal the jar, and what’s inside?
"That’s a perfect cultural medium for botulism," Taylor says.
In 1919, olive-related botulism outbreaks started killing people.
In August, 14 people got sick after a dinner party at a country club near Canton, Ohio. Seven of them died.
A week later, epidemiologists went to work, interviewing the survivors. Pinpointing the olives as the source of those deaths involved some great detective work. Their report includes:"
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You'll have to read the short and fascinating article yourself...
http://www.marketplace.org/topics/business/ive-always-wondered/why-green-olives-come-jars-black-ones-come-cans
btw I really like green olives, but I'm not that fond of black ones. personal taste thing.
= new reply since forum marked as read
The delicious little nuggets are pickled in brine; they don't rely on the jar or can to keep them fresh so they can be packaged however is most practical. Virtually infinite shelf life, too.
They're even available in (not-hermetically-sealed) 5-gallon plastic buckets if you REALLY like them 
Thanks for the post. 