Pistachios are an ancient nut. They have been consumed by humans for about 9,000 years and are one of two nuts (the other is the almond) mentioned in the Bible. Interestingly, pistachios are botanically related to the mango and cashew nut (so if you have an allergy to one, you may be allergic to the others.) In Iran, which is one of the world's largest pistachio producers, the pistachio is called the "smiling nut," and in China, it's referred to as the "happy nut," due to the nut's open-mouthed appearance when the shell is cracked. Happy and smiling can also describe how we feel and look when we eat them.
Pistachios are sold in their shells and shelled. If you love the taste of pistachios but hate having to pry the shell apart, shelled is your best option—but you will pay close to double the price. (And you will probably eat more, as studies have shown that removing pistachios from their shells slows your consumption.)
When purchasing the nuts in their shells, look for blemish-free, ivory-colored shells that are split open at one end. Avoid pistachios that are cracked beyond their natural opening. Unopened shells—besides being nearly impossible to peel open—are an indicator of immaturity. The kernel, or nutmeat, should be yellow to dark green in color. The greener the nutmeat, the better the flavor.
Unshelled and shelled pistachios are available in bags year-round in many forms, including raw, roasted, salted, unsalted, and seasoned. For cooking purposes—and to keep your fingers from getting stained—it is best to choose pistachios that have not been dyed either green or red, which is often done to cover up blemishes. (Luckily for us, almost all domestically grown pistachios are sold without dye.)
Once you remove the shell, you'll find the nut covered in a thin, edible paper that can be easily removed from the nutmeats by blanching, if desired. After parboiling, drain and slightly cool the pistachios before slipping off the skins.
Since the shell splits upon ripening to expose the nutmeat, pistachios have a limited shelf life. If keeping the nuts for just a few days, you can place them in resealable bags and store in the pantry. For a longer storage period, place pistachios in an airtight container in the refrigerator or freezer. Unshelled nuts may be stored for three months in the refrigerator or up to one year in the freezer. To prevent condensation when thawing, place the nuts in a plastic bag. Shelled pistachios can be stored in the refrigerator for up to three months but are not good candidates for freezing.
To refresh pistachios that have lost their crunch, toast them in a 200 F oven for 10 to 15 minutes. In addition to eating pistachios out of hand, they are a delicious ingredient in sweet and savory recipes. Depending on how they are purchased (shelled or in the shell) the weights and measurements can vary.
Honselman CS, Painter JE, Kennedy-Hagan KJ, et al. In-shell pistachio nuts reduce caloric intake compared to shelled nuts. Appetite. 2011;57(2):414-7. doi:10.1016/j.appet.2011.02.022