I was asked what I thought and how I feel about the prevalent custom in our city’s community to refrain from eating black olives during the entire month of Nissan. My custom is also not to eat them, and may I say that the customs of the people Israel are considered as Torah.
Being that it was during this month that the Almighty took us out of slavery in Egypt, and that we were commanded to “Remember this day when you left Egypt”, and that our sages, of blessed memory said [concerning olives], “the father [the source, i.e. the olive] causes memory loss and its outcome [oil] clarifies [thought], they had the custom of refraining from eating olives, their reason being that eating them causes forgetfulness. We are commanded to remember the miracles performed for us during this month. In order to cherish the commandment in a timely way, on the date and time that the miracles happened, it is not right that we eat something that causes forgetfulness.
The reason for singling out black olives is because oil is usually drawn from them. They said that "the source causes forgetfulness" concerning the olive whose son [outcome] clarifies, and the ones that are common during this season are generally the black ones; the green ones are less common. Their ruling concerns the ones that are common, so they did not rule concerning the less common ones.