Capers are the unopened flower buds of the caper bush, Capparis spinosa, a shrub of dry climates whose range runs from the Mediterranean south into Africa and east across Asia. They are picked by hand before they open, then cured in salt, brine or vinegar. They are not fish eggs or seeds: the bush's seeds form inside its fruit, the caperberry.

Are capers a fruit or a vegetable?

Botanically a caper is a flower bud, not a fruit, and in the kitchen it is used as a seasoning or garnish rather than eaten as a vegetable. The caper bush's fruit is the caperberry, which forms only after a flower opens and is pollinated. In the Mishnah, compiled around 200 CE, Rabbi Akiba held that only the caper bush's berries count as fruit.

What is the difference between capers and caperberries?

Capers are the caper bush's unopened flower buds. Caperberries are its immature fruit, which forms after a flower opens and is pollinated, and they are much larger. Both are pickled, and caperberries are eaten like pickles or olives.

What do capers taste like?

Cured capers are salty and tangy, with a sharp bite that Purdue University's caper factsheet compares to mustard and black pepper. The bite comes from methyl isothiocyanate, a mustard oil that forms from the bud's glucocapparin when its tissue is crushed. Sources disagree about raw buds: Purdue calls them bland, while Italian food scientists describe a bitter taste that brining neutralizes.

Why are capers so expensive?

Because they are picked by hand. The buds are small and delicate, so they are harvested one at a time each morning as they reach the right size, and the University of Wisconsin's extension service says that labor is what makes capers expensive. The smallest buds are the most valued.

Where Do Capers Come From? Buds of a One-Night Flower

A caper flower opens at dusk and is spent by the next day, a 2023 study in the American Journal of Botany reports: one large white bloom, one night. Every caper in a jar is a bud picked by hand before that night came.

Where do capers come from?

Capers come from the caper bush, Capparis spinosa, a shrub of dry climates whose range runs from the Mediterranean south into Africa and east across Asia. Each caper is an unopened flower bud, picked by hand and cured in salt, brine or vinegar. A bud left to flower and set fruit becomes a caperberry.

Whether the bush is native to the Mediterranean is unsettled. The University of Wisconsin’s extension page says it is not clear whether it is native “or just naturalized,” and the most popular hypotheses, the 2023 paper notes, make it a relic of an ancient dry-tropical flora, probably from Africa or western Asia.

Purdue University’s 1998 NewCROP factsheet lists Europe’s sources as Spain, Provence in France, and Italy, “especially Sicily and the Aeolian island of Salina and the Mediterranean island of Pantelleria.” Pantelleria’s capers, preserved in sea salt, were registered as a geographical indication in Italy in 1993 and EU-wide in June 1996, WIPO Magazine reports.

The flower opens at dusk and lasts one night

An open caper flower has four white to pinkish-white petals and a spray of long violet stamens. Its scent, white petals and nighttime opening fit night-flying hawkmoths, the pollinators the 2023 authors predicted.

A motion-activated camera then recorded three bushes on the Greek island of Lesvos over six nights in 2014. Most visits came from honeybees, which took pollen without touching the stigma, so the authors class them as pollen thieves. Carpenter bees, which could brush the stigma as they fed, visited eight times more often than hawkmoths, at dusk and the following morning.

Pickers take each bud by hand, and the smallest pay best

Because the buds are small and delicate, “they have to be harvested individually by hand, instead of by machine, each morning just as they reach the proper size,” the Wisconsin page says. In southern Italy, buds are collected by hand “about every 8 to 12 days,” Purdue’s factsheet says, for 9 to 12 harvests a season.

“Harvesting labor is what makes capers expensive,” the University of Wisconsin’s extension page says.

Size sets the value. In Italy capers are graded from 7 to 16, their size in millimeters, and Purdue’s factsheet says buds under a centimeter across are worth more than the larger grades. Other kitchen crops share the bottleneck: Ceylon cinnamon is peeled from the stem by hand, and US sesame could not be harvested without hand labor until 1982.

The bite is the bud’s own mustard oil

The caper family sits in the plant order Brassicales with cabbage and mustard, and the caper and mustard families “have long been known to be closely related families,” as a 2002 study of their chloroplast DNA put it.

Like those relatives, the caper bush makes compounds called glucosinolates. In intact plant cells an enzyme, myrosinase, is kept apart from them, the Linus Pauling Institute at Oregon State University explains. When the cells are damaged, the two meet and form isothiocyanates, the mustard oils behind a pungent aroma and spicy taste.

In raw caper buds the main glucosinolate is glucocapparin, about 90% of the total in a 2002 analysis of wild capers from Turkey. Its mustard oil is methyl isothiocyanate, which Purdue’s factsheet credits with the caper’s strong flavor.

When food scientists in Turkey analyzed the aroma of fresh buds for a 2019 study in the Journal of Food Science, methyl isothiocyanate was the most potent of the 12 aroma-active compounds they found, with a flavor dilution factor of 512.

Curing cut aroma compounds by two-thirds in one study

In the traditional method, as a 2022 paper from the University of Messina describes it, fresh buds are mixed with sea salt, 30 to 40% of their weight, for about 8 to 10 days while a brine forms and fermentation occurs. The brine is then poured off and the buds are salted again for 20 to 30 days; other capers are pickled in vinegar instead.

In the 2019 study, fermentation cut the total amount of aroma compounds in the buds by 66%, from 62,616 to 21,471 micrograms per kilogram, and total phenolic compounds by 78%. In the fermented buds the most potent aroma was acetic acid, the acid in vinegar. That is a single study of one fermentation.

The usual explanation mixes up two molecules

Popular accounts credit the cure with the bite. “Intense flavor is developed as mustard oil (glucocapparin) is released from each bud,” the Wisconsin page says, and Wikipedia’s caper article likewise credits the cure. Glucocapparin is the stored precursor, though, and the mustard oil is methyl isothiocyanate, which forms when the bud’s tissue is damaged.

The cure does matter: the Messina paper says fermentation develops the volatile compounds behind the caper’s “unique sensory features.” It builds much of a cured caper’s aroma, while the precursor of the bite is already in the fresh bud.

Sources also split over how the raw bud tastes. Purdue’s factsheet says “Raw capers are bland flavored and need to be cured to develop their piquant flavor.” The Messina team brined fresh buds “until the capers’ bitter taste was neutralized,” and in the 2019 measurements the mustard oil was the most potent aroma in the fresh buds.

Rabbi Akiba held that only the caper berries are fruit

A Gotham Bagels blog post calls capers, “technically speaking,” a fruit. Botanically a caper is a flower bud. The fruit is the caperberry, and Tablet notes that mature fruit “are less desirable, as they contain hard seeds.”

Part of the bush	What it is	How it is eaten
Caper	Unopened flower bud	Cured in salt, brine or vinegar
Caperberry	Immature fruit	Pickled, eaten like pickles or olives
Ripe fruit	Mature fruit with hard seeds	Less prized because of the seeds
Young shoots	Stems with small leaves	Eaten as a vegetable or pickled

The question is old. In the Mishnah, the first major work of rabbinic literature, compiled around 200 CE, Rabbi Eliezer said tithes were due on the caper bush’s shoots, berries and blossoms. Rabbi Akiba disagreed: “only the berries are tithed since they [alone] count as fruit,” in Joshua Kulp’s translation.

The Mishnah’s Hebrew word for the berries, aviyonot, appears in the singular in Ecclesiastes 12:5, where the King James Bible reads “desire shall fail” and the New American Standard Bible “the caper berry is ineffective.”

By Rabbi Akiba’s rule, a jar of capers holds no fruit and owes no tithe. Every bud in it was picked in the morning, before its flower could open at dusk and set a berry. Strictly FYI.