Because the altar is treated as a place where deceased family members are still present in the household — and in Vietnamese culture, presence is acknowledged by offering food. Fruit is chosen because it is fresh, fragrant, beautiful, and lasts long enough to be offered respectfully.
An ancestral altar (bàn thờ) typically holds photographs, an incense burner, flowers, and a plate or bowl of fruit. In southern families you often see the mâm ngũ quả, a five-fruit tray arranged for Tết, where the fruits are chosen partly for their names and the wishes those names suggest.
The logic is continuity. The family did not end when someone died — they simply moved to a different place in the household. Offering food is how any Vietnamese guest is honored, and ancestors are treated no differently.
Offerings are usually made and then, after the incense burns down, shared and eaten by the living family. Nothing is wasted. Many people describe this as the point: the food passes through the ancestors and comes back to the table.
Fruit specifically tends to be preferred for daily offerings because it does not spoil quickly, needs no cooking, and looks generous. On death anniversaries and holidays, full cooked meals are often offered instead — sometimes the dish the person loved most.
No. Practice varies widely by religion, region, and generation. Catholic Vietnamese families often keep a photograph and pray rather than offer food; some households have no altar at all; some keep one only at a grandparent’s home.