Fido versus others - the rubber seals

[Ido]

Hi all,
I'm going thru phases with the different kind of jars and lids, thinking again of the Fido type (thanks to a link by Christopher I actually tightened mine, a non original Fido that was too loose. not sure I can even get an original Fido and I wouldn't ship a glass jar by mail…).
My question: does anybody know in depth of the different rubber seals and their behaviors? Is the Fido really different than other "good" brands? How are we so sure it won't let in the outside air after the initial pressure release (what y'all call "burp")? Maybe that is more to do with the conical shape of the lid and less about the rubber type? I'm more concerned with the air coming back in. I think that's what screws up long ferments.
If there was a video showing this stuff that would be very nice.
cheers

[Christopher Weeks]

I don't know anything technical about the rubber and I sort of stopped researching once I found out that Fidos were so good and the others that I had easy access to were not. However, I don't typically burp my Fidos. If I'm doing a ferment that I want to access while it works, I'll do it in an open-top jar.

We know that the Fido gasket adjusts to accommodate substantial pressure differential. When lots of CO2 builds up in the jar it pressurizes and eventually the differential is big enough that we hear the gasket hissing intermittently. That stops after a while, as the fermentation slows down, but I've opened Fido's months after closing them and just then, stuff hisses out. In those cases, I know that it's out-bound because bubbles come out of solution in the brine and it fizzes up. You wouldn't see that if air was rushing in, instead.

That said, I'm pretty sure that ferments generate negative pressure under some circumstances and if the pressure differential is great enough, I have every reason to believe that the Fido will admit outside air. I'm just not sure it every actually happens.

I hope you get more informed responses below, but I figured it was worth including my thinking.

[Ido]

thanks Christopher