Does thunder cause milk to turn sour?
'The popular belief that thunderstorms cause milk to turn sour is very old. In 1739 John Mottley published Joe Miller's Jests, or Wit's Vade Mecum (commonly called Joe Miller's Joke Book), which contained more than a thousand jokes, each with a serial number. No. 997 asserted that "the celebrated organist Abbe Vegler" once imitated "a thunderstorm so well that for miles around all the milk turned sour." The belief may have a slight foundation in fact. In 1939 scientists in Toledo, Ohio, announced that they could sour milk by sound waves and then sweeten it again by reversing the process. Originally the belief was that the electricity in the atmosphere during a thunderstorm caused the milk to sour sooner than it normally would. There used to be a notion that an electrical storm had the same effect on beer. It is probable, however, that there is not much connection between thunder and the souring of milk. Thunderstorms frequently occur toward the end of hot summer days. On such days milk is also likely to turn sour. This may be the only connection between the storm and the souring of milk, which is caused by the growth of bacteria.'
From "A Book About A Thousand Things" by George Stimpson.