A Staff Report from the Straight Dope Science Advisory Board

Why is it that green olives come in glass jars but black olives come in cans?

August 4, 2009

Dear Straight Dope:

Let me begin by saying I hate olives. That said, a curious question was posed to me by my mother recently and has begun to work its way under the skin. It appears that, without fail, green olives are packaged in a glass jar, black olives in a can. I have never witnessed an exception to this strange unwritten rule. Is this a conspiracy? an arbitrary decision passed down by the Illuminati? Please help.

Eutychus replies:

Lots of you have inquired about this, but you're all asking the wrong question. Some black olives do come in glass jars. The real question is "How do they get the olives to grow with pimento stuffed inside them?"

OK, OK, jars vs. cans. Let's start with green olives. Green olives are picked before they are ripe and are packed in jars, brine-cured for eight months, and then bottled cold. You can also let the olives stay on the tree and ripen until they turn either purple or black, then pick them and pack them the same way. Olives in brine remain edible for many years stored in jugs, crocks, or jars in a pantry. No refrigeration is required.

Canned black olives are different, though – they're ripened artificially. The back story: Olives used to be grown almost exclusively for use in making olive oil. But in the late 1800s there arose a widespread demand for pickled olives. Lots of different olive packaging methods were tried, but none was practical for large-scale commerce until George Colby and Frederic Bioletti, researchers at the College of Agriculture at the University of California, Berkeley, perfected a method for packing olives in metal cans. It was a doctor's widow, Freda Ehmann, though, who really made it profitable. Starting almost from scratch in the 1890s, Ehmann took a small olive farm and turned it into one of the first major companies in the United States to sell olives as a fruit; more than any one other figure, she created the national market for what became known as "California ripe olives." According to Judith M. Taylor and Kevin Starr in The Olive in California, at first Ehmann "sold her olives in barrels, kegs, and then glass jars." By 1905, however, she'd adopted the Bioletti/Colby method and did a booming business until 1919, when a botulism outbreak ended her run at the top of the canned olive game.

So: what is the artificial ripening process that makes it necessary to can canned olives? I spoke to Rosemarie Fusano of the Fusano Olive Company and she gave me the rundown:

Once harvested, [the olives] are placed in a water/lye solution in a holding tank where oxygen is piped in. After 24 to 48 hours the lye is washed away and the olives have turned black from the addition of oxygen. The purpose of the lye is to penetrate the fruit almost down to the pit. This makes the olive edible right from the start. Once the lye is washed away, a fresh brine solution is prepared and ferrous gluconate is added, which sets the color. The olives are then ready to be canned. A light brine solution is prepared and added to the olives in the can. Because the olives are then in an anaerobic environment, the chance of botulism developing is great. Therefore, the fruit must be cooked in cans for a certain amount of time.

So you can't process artificially ripened olives in jars – the glass wouldn't withstand the cooking temperature.

Because green olives don't undergo the addition of oxygen and are packed in brine, in which the salinity and the pH levels are high and low enough, respectively, to inhibit bacteria growth, they don't have to go through the addtional step of having to be sealed in metal and cooked.

Besides, they look pretty in glass jars.

And that's olive what I know.

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Staff Reports are written by the Straight Dope Science Advisory Board, Cecil's online auxiliary. Though the SDSAB does its best, these columns are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.


Taylor, Judith M. and Kevin Starr. The Olive in California. Ten Speed Press, 2004.

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