Pistachios are one of the oldest nuts around--we have been eating them for at least 9,000 years. They are also one of two nuts mentioned in the Bible, and interestingly enough, are related to the mango. In Iran, one of the largest pistachio producers, it is called the "smiling nut" and in China, it's referred to as the "happy nut" due to its "open-mouthed" appearance once the shell has cracked. It could also be because of how we feel after we eat them!
Pistachios are sold in their shells and out of their shells. If you love the taste of pistachios but hate having to pry the shell apart, shelled is your best option--but you will pay more, almost double. (And you will probably eat more, as studies have shown that removing pistachios from their shells slows your consumption.)
If 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 the natural opening). Unopened shells--besides being almost 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 for just a few days, you can place 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 nuts in a plastic bag. Shelled pistachios can be stored in the refrigerator up to three months, but are not good candidates for freezing.
To restore pistachios that have lost their crunch, toast them in a 200 F. oven for 10 to 15 minutes. For pistachio equivalents and recipes go to these articles: