Kefir have been brewed for thousands of years, it survived the ages with no problem! Kitchens have become cleaner and there is not one person that I know of that had ill effects or contamination. Some studies have shown that Kefir wards off Salmonella and E. Coli and can also Kill Helicobacter Pylori, which is quite impressive! Kefir has a natural defense mechanisms to keep the colony of beneficial bacteria and yeast safe from invaders, the same type of bacteria and yeast is active in your gut and helps your body to absorb food better, it boosts your immune system and helps with so many things including your general well being. Most people’s gut’s are imbalanced and that’s where stuff like Kefir comes in to help bring back the balance so that your good gut bacteria and yeast can fight for your health even when you’re asleep! It may take some time for the body to get used to probiotic rich foods and may cause a die off of bad bacteria and yeast (Herxheimer reaction) which may cause flu like symptoms. You can stick it out and wait for it to pass or reduce the quantity and gradually increase as you feel need be. Only you can tell what’s best for your body and your health.