Hi Mickhael
Its a bit of a proces. But here goes.
First make sure your pressure cooker can do 3 bar plus. I used the wifes pressue canner she makes her preseves with. Then get glass console bottles the size you want. Dont do to big. The ones with the ring lid not the normal screw top they wont seal propperly.
Sterlize the jars cut your tuna in pieces to start packing your jar.
Pack a tight layer with no air spaces. Put a small piece of fresh garlic if u like to in between layers. No salt or anything at this piont. Keep layering with no air gaps untill jar is filled to 1 cm from top. Give a moderate sprincle of course salt and some whole black pepper if you like.I then filled the jars with lemon infused olive oil. But this is not needed.close lids just untill tight dont tighten otherwise your jars will burst.
In the pressure coocker fill with watre about three qauters the depth of your jars.get water to temp.before inserting packed jars.
Nb.nb. dont put jars flat on the bottom they must be suspended on a wire rack. Close cocker top and coock for 90 min from when the pessure is up.
When done open lid take out jar. And tighten lid as tight as possible. Let cool outside and bon apetite. Store jars in a cool dark place. They are good without refrigeration for about three months never kept any longer so i dont know.Done chicken breasts the same way and just as good for a quick bite.
As with all fish work clean.if not done right you coul get seriously ill.
Regards
Malboer