In the Temple of Jerusalem, the most fragrant service of the day was the burning of the ketoret, the compound incense of eleven spices that rose in a thin column from the golden altar inside the Holy. The preparation of this incense was not a job for any priest. It was a hereditary craft, and one family, the house of Abtinas, held the secret.
The Mishnah in Yoma 3:11 records that this family refused to teach their art to anyone else. At one point the Temple directors, angered by the refusal, removed the Abtinas family from the service and imported specialists from Alexandria, in Egypt, to prepare the sweet perfume. The Alexandrian experts failed. Whatever they mixed did not rise the way the incense of Abtinas rose, a straight column that bent neither left nor right. The directors had to come back and ask the family to resume, and the family, knowing their worth, only agreed if their fee was doubled.
Why the secrecy? The Talmud records their own answer, preserved in Harris's 1901 Hebraic Literature. We feared that we might teach the formula to some unworthy person, who would then use the knowledge in idolatrous worship. The spices that made Israel's altar column ascend could, in the hands of an idolater, make a pagan altar smell just as sweet. The Abtinas family refused to let the fragrance of the Beit HaMikdash be counterfeited.
And there is one more detail, almost ethical poetry. The members of this family were careful never to use perfume of any kind on their own persons, so that no one could ever say, They are putting the sacred ingredients to personal use. They lived unscented so that the incense of Israel could remain unrivaled. The guardians of the smoke walked through life smelling of nothing at all.