National Pistachio Day

What the day is

National Pistachio Day is observed on February 26. The pistachio is the only common nut sold already opened, and it opens itself.

Origin and background

As the kernel matures it expands until the internal pressure splits the shell along a seam, audibly, while still on the tree. Growers regard the split as a ripeness indicator rather than a processing step. Nuts that fail to split are separated out and sold shelled, because a closed pistachio is difficult to open by hand and generally less mature.

The tree is unusual in several ways. Pistachios are dioecious, meaning individual trees are male or female, so an orchard needs both and only the females bear. They also show strong alternate bearing, producing a heavy crop one year and a light one the next, which makes supply and price swing on a two-year cycle. And they take years to come into production, so an orchard is a long commitment.

The growing conditions are demanding in a specific way. Pistachios need long hot summers and, crucially, enough accumulated winter cold to break dormancy, which restricts them to a narrow band of climates. Iran, Turkey and the United States dominate production, with California supplying most of the American crop.

The green color comes from chlorophyll retained in the kernel, and it varies with variety and maturity, which is why some are noticeably greener than others. The red pistachios older shoppers remember were dyed, a practice that began to disguise staining on imported shells and largely disappeared once harvesting methods improved.

Pistachios are relatively high in protein and lower in fat than most nuts, and the shells themselves are useful evidence: leaving them in the bowl gives a visible record of how many you have eaten.

How to take part

• Use half a shell as a lever to open a stubborn one rather than your teeth.
• Buy unsalted and season them yourself if you eat a lot of them.
• Leave the empty shells visible, which genuinely moderates how many you eat.
• Try them in something savory, where they work better than most nuts.
• Store them sealed and cool, since the green fades and the oil turns.