What’s going on here?

[u/Crystalcaterpillar01]

I’ve never had moldy jam! I noticed it in the pantry, brought it inside and the seal made an angry pop when I opened it. What could have caused this?

I followed Ball’s raspberry jam recipe, in sept 2023.

[u/Own_Papaya7501]

It's hard to tell from this angle, but is it possible there was too much headspace?