Leave the mixing ball in right until you have finished consuming all of the kefir in your jar.
You will need this to help you when you shake it up each time before eating or drinking as it will separate again during storage.
Generally, kefir should not be in contact with metals as metals are prone to leach under acidic conditions (kefir is acidic). However, as our mixing ball is stainless steel, there is no issue using it. Stainless steel is considered safe and inert and does not leach.
Metals such as copper, brass, zinc, iron and aluminium are reactive at a low pH (acidic environments) and are considered unsafe.