I am cooking a pork butt roast sous vide. I am following this recipe. https://recipes.anovaculinary.com/recipe/sous-vide-bbq-pork-shoulder

My bag had no or very little air in it after sealing and when the cooking started. Since cooking for a few hours the meat has shrunk considerably in size within the bag. But the bag also has new air in it. Enough to make it float.

I am worried I could have bad bacteria and make my guests sick.

Here is more of my thoughts: 1) According to some articles I have read this could simply be vapor. At 165F the meat is hot enough to release some water to vapor. 2) Maybe while coming to temperature some bacteria did grow, but at 165F, that bacteria is now dead. Even though the air remains, the meat is safe to eat. The dead bacteria and/or their waste are not harmful. 3) I grew a bunch of bacteria and this is not safe to eat.

Here are some pictures: http://imgur.com/a/ARlbT

FYI, This was the only other SO post I found: Ziploc vacuumed bags expand in sous vide