Review on 500Cc Oxygen Absorber Packs - 50 Pack (5 X 10) By PackFreshUSA: Non-Toxic Food Grade For Long-Term Food Storage & Preservation With Guide Included by Matt Charlton

Using 2, 8 oz mason jars with new rings and lids, place a 500 cc quickly in one of the jars and tighten up the lid so air cannot leak. In the other jar put nothing, but tighten up the lid also. To be sure wait 24 hours, but tapping on the lids with a wood chopstick holding the narrow end (or any substitute you feel ok using) the difference in sound will tell the story. Also you should see the center 'button' of the lid with the o2 has collapsed but not on the other jar without an o2. (You may also hear the button ping within a few minutes.) Use caution that 'you' don't push the lid button down. This may work with larger jars, I didn't test though. To clarify, you don't have to wait 24 hours to hear the sound difference, most likely, but if none is noted early it's best to wait 24 to be sure. This brand passed my test.