Question

sometimes you may notice a black powder or white discs floating on the pickle or muramba when a jar is opened by your mother after a long time what exactly are these why are such food items not good to eat how can the pickles or murambas be preserved safe for a long time?

Answer 1

i think its fungus grown due to moisture content and eating it causes food poisoning.

Answer 2

they have been oxidised from oxygen of air.
the aerial oxidation of fats and oil containing food items get oxidised marked with unpleasant smell and taste is called rancidity.
it can be preserved by using anti - oxidants.

hope it is helpful