Herbsaint Liqueur is an anise-flavoured American-made version of pastis.
It is made in New Orleans by Legendre Distilleries.
It is a clear greenish-amber colour that you can see through, though it turns cloudy in water. It is not as sweet as Pernod.
It is made by the Sazerac company. The company officially refers to it as "Liqueur d’Anis."
The recipe is secret.
Herbsaint Liqueur is used in making Oysters Rockefeller, and in making the cocktail called "Sazerac."
Legendre had been stationed in France during World War I in the American Intelligence Service. There, he made friends with an Australian fellow named Reginal P. Parker while they both attended some intelligence training courses in Le Havre. Parker was later posted in Marseilles and boarded with a family, from whom he learnt how to make pastis.
After the war, Legendre returned to New Orleans and went into the drug store business owned by his father, Joseph A. Legendre (died 1926.) Prohibition set in, but the Legendre drug stores had a licence to procure and sell prescription whiskey. Sometime after this, Parker and his mother moved to New Orleans. Parker decided that he wanted to make pastis privately in New Orleans, for private consumption. He had Legendre use his drug store business contacts to import the herbs needed, and he used the prescription whiskey that Legendre had access to as the alcohol. He gave Legendre a recipe so that Legendre would know what herbs to procure.
When the end of American prohibition came into effect on 1st December 1933, Legendre was well positioned to make the pastis for sale. He had all the contacts, and the recipe; he just had to obtain a permit to make it for sale, which he did.
He first made Herbsaint for sale in 1934 with no wormwood in it. He tried calling it "Legendre Absinthe" (even though there was no wormwood at all in his recipe, so it wasn't really absinthe) but he found that the name "Absinthe" was illegal, so he quickly changed the name to "Herbsaint."
He found that it really wasn't profitable enough for him to bother trying to run as a business, on top of the drugstore trade. So, he sold Herbsaint to "The Sazerac Company", with the sale coming into effect on 1 January 1948.
Before 1948, the label on the bottle said that the bottler was Legendre & Company. From 1948 to autumn 1956, the label said that the bottler was Sazerac Co. Inc. After that, the label said that the bottler was Legendre Company. The label was changed in 1958, and in 1961. Since 1961 there have been several small tweakings of the label up to the current date (2006.)
In 1944, Herbsaint advertised itself as "100 proof" (aka 50% alcohol).
By 1958, the company was making a 90 proof (aka 45% alcohol) version; the 50% version was dropped in the 1970s.
In the mid-1930s, they also made a "120 proof" (aka 60% alcohol) version. It was made in mini-bottles, at least (perhaps also in large ones, but some collectors still have the mini-ones), and was mentioned in a 1951 booklet they produced.
Confusion about how and when Herbsaint was first made comes from some fanciful, inaccurate advertising copy in a 1944 booklet the company released. Legendre employed a William B. Wisdom to write the copy for that booklet, and said he found that Wisdom had a very "fertile" mind. Wisdom invented some history, writing that the recipe for Herbsaint "has been a long-guarded treasure of the Legendre family, a prized possession handed down from father to son. During all the years, the Legendres pride themselves on the fact that they have never deviated from the original formula of their forebears." Legendre was a bit worried about this fabricated history: "I told him that this might be questioned but he said 'It is of no great importance.' " 
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-- Julia Child (15 August 1912 - 12 August 2004)