Chicken Family

My mom and I canned some raw chicken breast today. She’s done it many times before and felt confident with the process. However, one of the jars looks a little foamy. It did seal properly, although a couple of the other jars did not.

We're wondering if the foamy jar is unsafe and should be discarded. My mom has never seen this happen before. She didn't notice the foam when the jars first came out of the canner, but it's possible that side was facing away from her, or that the foam developed during the first hour while the jars were cooling.

Has anyone experienced this before or know what might cause the foam? We'd really appreciate any insight. Thanks in advance!

Looks like my canning season has officially come to an end.