It is believed that when tofu is boiled with grated daikon radish, for some reason, no bubbles form inside the tofu (writer named Shotaro IKENAMI writes that it is good to add chopped radish for the same reason when making boiled tofu).
大根おろしの中で豆腐を煮るとなぜかスがはいらないという（同じ理由で湯豆腐に刻んだ大根を入れるとよい、と作家の池波正太郎は記している）。