[crygin]

It's a combination of temp & time -- 131F for four hours will pasteurize (and, conveniently, is below the coagulation temperature for both the white & yolk of eggs, so you can home-pasteurize eggs for mayo/etc with a water bath). Contrariwise, 140F wouldn't be safe if it only reached it for a few seconds.

[abakker]

yeah, the difference being the time...hence my original question. At 135 degrees you need at least 35 minutes of hold time once you have reached the target temperature.

http://sousvide.wikia.com/wiki/Importance_of_temperature_con...

[lifekaizen]

correct. that's why it's beautiful to control the entire process with software -- we know your time/temp curve. And why the USDA still gives one temperature which assumes an instantaneous point of contact, but higher than you need if you can simply hold the temp. (As a heuristic, staying lower gives you better quality food.)