Fennel Seed vs. Anise Seed: Two Plants, One Licorice Compound

Fennel seed and anise seed both taste of licorice, and they get it from the same compound, anethole, even though they come from two different plants. Anise has more of it: its oil is 80–95% trans-anethole, against up to 70–80% in sweet fennel, though those figures come from different samples.¹² Anise is the stronger, sweeter licorice of the two, and fennel seed is the lighter one. You can swap one for the other in a dish with lots of spices, but America’s Test Kitchen’s tasters easily picked out the swap where the seed was the main flavor.³

Side by side

The two anethole ranges come from separate PROSEA entries, each summing up its own samples. They tell you which seed tends to carry more. We didn’t find anyone who measured the two side by side.

One compound, several spices

Anethole is why these two get mixed up. PROSEA calls trans-anethole the character-impact compound of anise,² and credits it with sweet fennel’s anise smell and sweet taste.¹ ATK traces the licorice flavor of anise seed, fennel seed and star anise to high levels of trans-anethole, and points out that each comes from a different plant with its own secondary compounds.³

• Star anise is a third anethole spice from an unrelated plant: Illicium verum, a tree in the Schisandraceae. Its oil is 70–93% trans-anethole.⁸ See star anise vs. anise seed.
• Tarragon often gets grouped with these, but a different compound leads its oil: methyl chavicol (estragole), at about 77% in one French tarragon oil PROSEA cites.⁹ See tarragon.
• Licorice isn’t a relative either. Anise’s flavor is often confused with licorice, and anise oil is traditionally paired with licorice in licorice candy.

How the differences show up in cooking

Strength. The Spice House calls anise closer in flavor to fennel but stronger, and says to use it more sparingly.⁶ Anise oil’s higher anethole range fits that,¹² though no study has measured the two seeds’ strength in a dish.

Where the seed is the main flavor. ATK swapped the three anethole spices in a biscotti recipe written for anise seed, and tasters easily picked out the differences. In Italian sausage meatballs, with lots of other spices, the differences were harder to detect.³ So here’s the practical rule: the more spices in the dish, the safer the swap.

Sweet and savory. Both seeds go both ways. Fennel flavors pastries, sweet pickles and fish; anise goes into pastries and the bread Anisbrot, along with the anise liqueurs absinthe, anisette and Pernod. Fennel is also a sausage spice. In the United States, anise is widely tied to pizzelle and biscotti, and fennel to Italian sausage and tomato sauce.

Bitter fennel. PROSEA splits fennel seed into a sweet type and a bitter type with a pungent, camphor-like smell and taste.¹ Labels rarely say which one is in the jar, so if your fennel tastes harsh next to anise, it may be the bitter type. That’s an inference, not a test result.

Mix-ups in the trade and in blends

The confusion is old and commercial. Fennel and anise fruits are often confused and substituted for each other,¹ and ground anise gets adulterated with ground fennel.² Buy whole seed and you can check: anise is the smaller one, about 3.5 mm against fennel’s 6 mm.⁴⁵

Blends show the same overlap. Britannica’s list for Chinese five-spice powder includes fennel seed,⁷ but McCormick’s Culinary Chinese Five Spice lists anise, cinnamon, star anise, cloves and ginger, with no fennel.¹⁰ The Bengali five-seed mix panch phoran uses fennel, both in the version Gernot Katzer says is most often printed and in Bong Eats’ recipe;¹¹¹² we found no version that uses anise instead.

Can one stand in for the other?

Yes, and it works best in savory dishes with other spices. These come from our substitute pages.

• Anise in place of fennel. Ratio (Attributed): The Spice House says to start with half to three quarters of the fennel amount and adjust to taste.⁶ See fennel seed substitutes.
• Fennel in place of anise. Ratio (Method): Start with the same amount and taste, adding more once the dish has cooked if you want the anise to come through. In a cookie where anise is the flavor you’d name, expect a difference.³ See anise seed substitutes.

ATK’s own advice is not to swap them where the flavor matters.³ PROSEA, describing the trade, says they’re often substituted anyway.¹ Both hold up: the swap works, and careful tasters notice.

Safety

Both seeds contain estragole: up to 5% of anise oil per PROSEA,² and present in fennel, which PROSEA notes is a liver carcinogen in mice.¹ The EU’s former Scientific Committee on Food concluded in 2001 that estragole has been demonstrated to be genotoxic and carcinogenic.¹³ We found no regulatory limit for estragole in either seed sold as a spice. For what regulators say about medicinal use, see fennel seed and anise seed.

What isn’t known

• The anethole figures come from separate summaries of different samples. We found no paired analysis of both seeds.
• We found no dated, sourced price comparison.
• We found no source for anise being used in place of fennel in panch phoran or in Italian sausage seasoning.

Related

• Fennel seed, fennel seed substitutes, fennel pollen vs. fennel seed
• Anise seed, anise seed substitutes
• Star anise, star anise vs. anise seed, star anise substitutes
• Caraway seeds vs. fennel seeds, fennel seeds vs. cumin seeds, fennel vs. dill
• Chinese five-spice powder, panch phoran, tarragon