My dear Shroomy, Not earthworms but sea worms!! When auntie was your age - I presume you are sweet 16- my Laska man, who comes around with an earthen pot of laksa gravy slung over his bamboo pole on one end and his ingredients and crockeries on the other end, has a little white bulging cloth bag thrown inside his pot of Laksa gravy. He said he place sea worms (the type you find on the sea shore sand) in the bag to prevent his gravy from turning sour. In those days i.e. 50/60 years or more, hawkers move around on foot and refrigeration was out the question.
click above for the full details!