[QUOTE=andymi86;10565345
Honestly, I will continue to carry my growler in my bag. Even if it were to break, I couldn't see the glass puncturing the bag..it's pretty tough. I would be afraid that a growler in a pannier would get super shaken up since it will see a lot more road vibration than if it were in a bag on my back.[/QUOTE]

I'd consider using my messenger bag to carry a growler, largely because I don't have a rack+panniers. However, broken glass is damn sharp--don't be fooling yourself about the glass not puncturing the bag. Damage might be mitigated by the fact that the glass would be more slicing than puncturing, and that you might not be grinding your back into it (and you do have one more layer as you mentioned). But you'd probably get hurt more.

Besides, we have empirical evidence above that the glass will poke through a pannier.