Please, use a bottle brush and a (small) tub with a PBW or Oxiclean (or just plain Washing Soda) solution to clean the inside and remove any potential biofilm. It only takes an extra 10-15 seconds per bottle for peace of mind. Rinse well, of course. I always used one of those jet spray washing attachments on the faucet.I'm thinking bottles aren't the culprit, but I should step up the cleaning and sanitizing of those anyway.