Fermentation Brine Percentage and Tannins

Fermenting vegetables is a pretty safe procedure, in fact, if done properly, fermented veggies are probably safer than raw. Really, little can go wrong if handled properly. The process is literally thousands of years old. In fact, your biggest concern is contamination after the process is complete. Of course you need to use safe food handling procedures to begin with (clean product, clean hands, clean containers...etc). Then you need to use the proper level of salt for the product you are fermenting--2.25% by volume up to 13 or 14% depending on the vegetable. The idea is to bring the product to a pH level of 4.6 or lower. Basically, using the correct amount of salt, at the correct temperature, for the correct amount of time achieves this. There are lots of online resources. Probably the foremost expert on ferments is Sandor Katz. He has an excellent book and an informative website.

If you can verify that your product was handled correctly (cleanliness, salt, temperature, time), there should be no reason that it is not safe.

I would advise if you are planning make often then I would invest in a gallon fermentation crock. It may cost you anywhere from $100- $200 but if you are making this often then i t maybe worthwhile for you as it will last you for many years and most come with weights already specific to the volume of the crock. My grandmother has one she uses for making kimchi