I've been fermenting these walnuts for a few months in a glass bottle, I'm just amazed they're still good although now they're starting to get bitter

I know the japanese ferment their miso for years, and the chinese ferment fish for a year. I wonder if it's ok to keep fermenting these walnuts or if they start to get hard to digest again after so long.

I've been eating them though and they don't bother me at all! What do you guys think?