From time to time, you may find a recipe that calls for blanched almonds, and mercifully, that's something you can readily buy in stores or online, although blanching almonds at home isn't hard to do. But blanched pistachios? That's not something I've ever seen for sale—though, should some specialty market have them on offer, I'd expect to pay a premium for the convenience.
Blanching pistachios is a simple act that can have a make-or-break impact on pistachio desserts. Still, it may be an easy task, but it's certainly not a speedy one. Pistachios are small and fiddly, with nooks and crannies where the skins like to stick (especially compared with the smoothness of an almond, and the ease with which its skin will pop off).
While it's not a technique every cook or baker will need to know, it's an essential for anyone with their heart set on homemade pistachio paste (à la Marco Colzani's Pistacchio spread) or pistachio gelato, or even a pistachio pesto if you're feeling fancy.
Pistachio Varieties: American Versus Sicilian
Pistachios come in a few varieties, so be sure to choose the right style for the recipe in question. American-grown pistachios (at left in the photo below) tend to be of the "Kerman" or "Peters" cultivars, both descendants of Iranian seeds imported to California in the 1920s, although many other types are grown on small-scale farms. These pistachios have a relatively round shape, with a nominally green nut under their papery brown skin.
When eaten out of hand, they have the flavor most Americans recognize as "pistachio," but in recipes, their flavor is often too mild to stand out in a sea of milk and sugar or flour. As a result, this type of pistachio has gained popularity as a snack food rather than an ingredient, though it can still work well in recipes that call on pistachios as an accent, whether for flavor or color.
Sicilian pistachios (at right) come almost exclusively from the "Napoletana" cultivar (sometimes called "Bianca"), which came from Syria to Italy way back in AD 30. These pistachios have a long and slender emerald nut covered by a leathery purple skin. Their rich and pronounced flavor can sing through other ingredients, making Sicilian pistachios a favorite among pastry chefs. As these represent less than 1% of pistachio production on a global scale, they're quite expensive—limiting their use to specialty applications rather than snacking.
Whatever the type you use, if you want an intense pistachio flavor in your dessert, those papery skins have to go. The negative qualities of the skin may not be obvious when you're chomping on a single pistachio, but when you're working with a large batch of nuts, they'll become abundantly clear as you set aside the skins and their unpleasantly musty smell, which calls to mind damp hamster bedding. (They won't do your recipe any textural favors, either.)
For anyone who's ever attempted to make a pistachio dessert only to wind up with lackluster results, those yucky skins can explain a lot. Aside from the fact that they contribute a strong and decidedly "not pistachio" flavor to whatever they touch, their woody aroma is only intensified by toasting, further muddying the flavor of the pistachios themselves.
How to Blanch Pistachios
The first step is to loosen the skins on whole, raw pistachios. While a quick soak in hot water is enough for almonds, per Daniel's excellent guide to blanching almonds, pistachios require a bit more heat.
Too much, however, and the nuts can turn mushy and soft, crumbling apart at the touch and making the act of peeling a nightmare. My personal preferred method is to soak the pistachios in cold water for five minutes, then heat them in a wide skillet until the water is steaming-hot (but well below a boil, or even a simmer).
When the skins are loose enough to slip off of a test pistachio, I drain the nuts into a colander and rinse with cold water so they're firm and easy to handle. (Hot pistachios tend to be crumbly and soft.) From there, the pistachios can be peeled in a number of ways. Which method you choose is largely a matter of personal preference, and I sometimes switch back and forth in my approach due to sheer boredom.
The first method is straightforward enough, and that's to simply peel the pistachios one by one by gently pinching off the skins. I place the sieve or colander of pistachios over a bowl to collect the excess water and skins, with another bowl nearby to receive the peeled pistachios. The downside to this technique is that the damp skins tend to stick to your fingers as they dry, so you're constantly trying to flick off bits of papery skin.
Another approach is to gather the pistachios in a clean kitchen towel and rub them through the cloth to start loosening the skin. For stubborn skins that refuse to let go, pinching the pistachios through the towel can provide the traction needed to get things moving. When most of the skins have loosened, pick out the peeled pistachios and discard the skins.
The downside to that technique is that rubbing may crumble the pistachios, particularly if they aren't completely cool. Plus, removing the skins in bulk means you have to pluck out the pistachios one by one, and many will still require a bit of manual peeling to entirely remove the skin.
My method is to put a handful of pistachios in a small bowl of water and peel them one by one. The water keeps the papery skins from drying on my fingertips; the skins will also float to the top this way, while the pistachios themselves will sink, making them easy to sort. When I've finished with one handful, I change the water and add a fresh batch of pistachios to carry on.
I'm not going to lie—it's mind-numbing work, whatever method you choose, so I highly recommend a bit of multitasking. Put on a pair of headphones and call a friend, fire up a good movie, or make like Tom Sawyer and convince some kids that it's a privilege to hand-peel a pound of pistachios.
Peeling will also give you a chance to sort through the pistachios and discard any that are withered, blackened, or otherwise gnarly and not fit to eat.
In the end, you'll have quite the mound of glistening pistachios beside a heap of ugly skins, and it's only in this moment that you can truly come to appreciate the importance of blanching.
It's a lot of work, to be sure, but it's well worth it; in my tests of pistachio spread and ice cream, I was blown away by the differences in flavor and color that blanched pistachios could provide, while those made with un-blanched pistachios were muddy and dull in both taste and appearance.
Blanching does allow the pistachios to absorb a bit of water, but that only makes them easier to grind into a paste. Otherwise, the gain can easily be accounted for in recipes that contain liquid already, simply by weighing the pistachios before and after soaking/blanching and adjusting the liquid in the recipe accordingly.
Otherwise, the blanched nuts can be tossed in a little oil (bonus if it's pistachio oil), then allowed to dry in a 200°F (90°C) oven. The exact time required will depend on the amount of pistachios in question, and how much water they absorbed during the blanching process, but expect this to take about two hours for a half pound of pistachios.
Working low and slow is key to driving off the moisture without over-browning the pistachios, which can ruin their delicate flavor. That said, if you'd like to crisp them (not all recipes will require this), the dried pistachios can be toasted for another eight to 15 minutes at 350°F (180°C) to further develop a toasty flavor and texture. Do bear in mind that less is more when it comes to toasting pistachios; while toasting can improve the flavor of many nuts, the roasted flavor itself can become a distraction in pistachios.
As you can tell, blanching (and potentially drying) pistachios isn't a fast or easy recipe hack, but it's a worthwhile technique with a tremendous payoff for the flavor, texture, and aroma of any pistachio-centric recipe. It may not be as useful in recipes where other strong flavors and textures come into play, but on those occasions when you want pistachios to sing, consider it an excuse to catch up with a friend, or your favorite TV show, and get to peeling!