Why not "one"?
"Grain" is a quantifier, generally used for round objects, equivalent to "pellet".
For example: a pearl.
Because traditional mooncakes are round, "pellets" are used when expressing the quantity of mooncakes.
Moon cake: Moon cake, also known as moon cakes, small cakes, harvest cakes, reunion cakes, etc., is one of the traditional delicacies of the Han nationality in China.
?[1]?Moon cakes were originally used as offerings to worship the moon god.
Sacrifice to the moon is a very ancient custom in our country. It is actually an activity of worship of the "Moon God" by the ancients.
Since its development, eating moon cakes and admiring the moon during the Mid-Autumn Festival have become indispensable customs for celebrating the Mid-Autumn Festival in various places in northern and southern China.
Moon cakes symbolize reunion, and people regard them as festive food, using them to worship the moon and give them to relatives and friends.