http://enquirer.com/editions/2001/06/25/tem_ask_a_stupid.htm...
http://www.straightdope.com/columns/read/2885/why-is-it-that...
http://lacrossetribune.com/tomahjournal/lifestyles/ask-your-...
It seems more like it has become a tradition of some kind in California.
More here:
http://oliveoilsindia.com/California-Olives.htm
it only applies to artificially made ripe olives.
... and seemingly this "high temperature" sterilization (which is still within 110-120 degree Celsius, so perfectly doable in glass containers) adds acrylamide:
https://www.ars.usda.gov/research/publications/publication/?...
in almost unbelievable amounts:
http://pubs.acs.org/doi/pdfplus/10.1021/jf5022829
Heck! 410 micrograms/Kg vs. 1.4 (Greek Olives) and 0 (Spanish Olives)!
http://www.whfoods.com/genpage.php?tname=george&dbid=260
>What About Acrylamide and Olives?
Research on olives and their acrylamide content has shown some inconsistency over the past several years and this inconsistency has sparked controversy in the public press about olives and their health risk with respect to acrylamide. In data assembled by the U.S. Food and Drug Administration (FDA), we've seen more than a dozen different kinds of olives, including Spanish, Greek, Kalamata, Nolellata, Sicilian, d'Abruzzo, and Gaeta, and di Cerignola that were determined to contain no detectable level of acrylamide. Yet we have also seen FDA data showing levels of acrylamide as high as 1,925 ppb in some canned, nationally distributed brands of black pitted olives. Based on this data, we suspect that these higher acrylamide levels in select canned black olives were related to specific handling, storage, processing (especially preservation and darkening methods), and heating steps that favored formation of acrylamide. It's also important to note here that we are not aware of any data showing problematic levels of acrylamide in any extra virgin olive oils available in the marketplace.
At present, we are not aware of any foolproof method that consumers can use to avoid purchase of canned black olives that contain unwanted amounts of acrylamide. Since the FDA data has shown no detectable levels of acrylamide in numerous samples of important olives packed in brine, those olives may be worth considering as options that may help avoid unwanted acrylamide. As stated previously, extra virgin olive oil is another form of this nutrient-rich food that, to our knowledge, has not been shown in research to contain unwanted amounts of acrylamide.
The last cited article reports however that as much as 1,925 ppb have been found in some specific canned olives.
https://www.fda.gov/food/foodborneillnesscontaminants/chemic...
This whole data set is oddly fascinating.