by opening the jar did I ruin the fermentation?

Not at all. Many folks use a type of semi-open fermentation where it is not fully sealed from the air. Think of pickle barrels or some kraut crocks.

All it means is that once opened to air exposure bacteria are allowed in and now you will have to skim off any scum that develops every couple of days.

Next time you won't want to fill your container nearly as full as you apparently did this time and weights are usually only used when solids (not liquids) are fermented.

If it blew the airlock and the lock was the correct size for the container then too much gas was allowed to build up inside the container. Cracking the lid open a bit every couple of days prevents that. That usually means too much kefir was added or the air temps are too warm.

Dave

Thanks Dave. It has now seperated in the middle. Is this something to be concerned about?

Just normal settling as with any mash. Just stir it up every few days. If you don't want to open the jar to stir just gently tip and roll it in your hands to mix the contents.

Dave