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pistachio ice cream raw (right) vs roasted (left)

How to Make Pistachio Ice Cream Green – Controlling Chlorophyll

Ever tried making pistachio ice cream? And ended up with brown ice cream? Not at all like the vibrant green pistachio ice creams you’d find in ice cream shops?

Turns out, creating bright green pistachio ice cream needs some help from (artificial) colors. But, if you’re ok with a light green hue, there are things you can to do bring out the green color, without adding (artificial) colors. All you need is some basic understanding of the color of pistachios and chlorophyll.

Introducing pistachio nuts

Pistachios are green/yellowish nuts, related to cashew nuts. They are native to the Middle East and Asia. Since they stem from this region, they can be found in a lot of Middle Eastern sweets and dishes, such as baklava. Nowadays though, they are also produced outside of that area. California (USA) and Italy are both big manufacturers for instance.

They’re green!

Have you ever realized that most nuts are brown? Peanuts, cashews, almonds, walnuts, they’re all brown. And yes, pistachios are also brown on the outside. However, once you take away their shells, you may encounter a bright green nut. Just how green depends on the variety. Some are more green than others, but all do have a green/yellow hue to them.

This unique color sets pistachios apart. It makes it a good candidate for a range of pastries, ice cream, and other snacks. Though of course, their flavor profile helps with that as well.

pistachio
Peeled pistachio nuts

What makes pistachios green

So where does this green color come from?

Color of food is determined by the presence of certain types of molecules. These molecules interact with light in such a way that it changes how we perceive it. They absorb and reflect light. Generally, these molecules are quite large and have special structures that allow them to do so.

We’ve written about natural colors in food elsewhere. We discussed that there are four main families of pigments that give color to foods: chlorophyll, carotenoids, flavonoids, and betalains. In pistachios, two of these families play a key role in coloring a pistachio nut.

Green is from chlorophyll

The green color is caused by the presence of chlorophyll. Chlorophyll is the driver behind most green colors in fruit and vegetables. Broccoli, Brussel sprouts, lettuce, and many many more vegetables are all green because of chlorophyll.

Chlorophyll gives plants a bright green color. Unfortunately, it is not very stable. A common reaction to occur is the transformation of chlorophyll into pheophytin. Pheophytin is still green. However, it no longer is bright green, it’s more of a dull green color.

Pistachios naturally contain both chlorophyll and pheophytin. The ratios depend on the pistachio nut variety, how it’s been grown and stored, and more.

Ripe vs. Unripe pistachios

Pistachios are a natural product. As such, they aren’t always identical in color. The concentration of chlorophyll and carotenoids can vary. The region they’re grown in and the weather during growing, both impact the color of a pistachio nut. It also explains why nuts from certain regions may be greener than those from other regions.

Aside from region and growing conditions, ripeness has a big impact on color. Notice how bananas lose their green color upon ripening? As do apples, (bell) peppers, mangos, and tomatoes. This change in color is not necessarily due to new colors forming. Instead, the driving force behind this color change is the breakdown of chlorophyll. When the strong color is gone, the other colors start to shine through. The same happens for pistachio nuts. Riper pistachio nuts are less green than unripe ones.

Added hues from carotenoids

So what’s ‘hiding’ behind the green in pistachios?

Most pistachios aren’t pure green. Instead, they might also have a yellowish hue to them, or even a little orange. This color comes from a group of molecules called carotenoids. Lutein and β-carotene are just two of the carotenoids present in pistachios. Carotenoids also give color to carrots, and many more fruits and vegetables. They are quite stable and not as easily broken down as chlorophyll is.

pistachio ice cream raw (right) vs roasted (left)
Pistachio ice cream, made using the recipe below. None are bright green. Left: made from roasted pistachio nuts, this adds roasted pistachio flavor but does make brown ice cream. Right: made from raw pistachio nuts, this ice cream has a light green/yellow color to it. Individual pieces of pistachio in the ice cream are still green.

How to keep pistachios green

As we mentioned, chlorophyll isn’t a very stable molecule. High heat, acidity, or just exposure to air can cause chlorophyll to lose its bright green color. In some instances it turns into a dull green, in other cases, it may lose its color completely.

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Do not roast them

Chlorophyll breaks down when you heat it for too long. As such, roasting pistachios is a surefire way to lose the bright green color.

What’s more, when roasting nuts you add new brown color to pistachios. During roasting, molecules react in the Maillard reaction which results in not just a brown color, but also a lot of flavor molecules.

There are a lot of great reasons to roast nuts, maintaining a green color just isn’t one of them!

Do not add acid

Chlorophyll is very sensitive to acidic conditions. The acidity speeds up the decay of chlorophyll into pheophytin. On the other hand, slightly alkaline conditions can help preserve the green color. So, stay away from adding strong acids.

Making bright green pistachio ice cream

Even if you’ve selected bright green pistachios, made sure not to roast them, and did not add any acids, your ice cream may still be a bland green color.

Ice cream simply contains too many other ingredients that mute the color. Milk, cream, eggs, corn starch, all dilute the green color. And you can’t continue to add on more pistachios. They’ll affect the texture of the ice cream too much. It may become grainy and lose its smoothness.

pistachio ice cream raw vs roasted (left)
Right: pistachio ice cream made with green, unroasted pistachios. Nevertheless, it still isn’t bright green.

So, if you really want a bright green pistachio ice cream, add some food colorant. Artificial food coloring generally is a lot more resistant to heat and processing. It won’t fall apart as easily as chlorophyll. What’s more, it’s often a lot stronger, so only a few drops might be enough to create a bright green color!

pistachio ice cream raw vs roasted (left)

Pistachio Ice Cream

Yield: 4-6 portions
Prep Time: 30 minutes
Additional Time: 50 minutes
Total Time: 1 hour 20 minutes

A simple pistachio ice cream recipe. Control color by deciding how to treat the pistachios, or simply add a little extra color.

Ingredients

  • 105g unsalted peeled pistachio nuts
  • 300g cream
  • 2 egg yolks*
  • 110g granulated sugar
  • 1,5 tbsp corn starch
  • 300g milk

Instructions

Prep the pistachios

  1. Option 1: Want a stronger roasted pistachio flavor and don't care about color too much? Roast the pistachios in a pan or pre-heated oven (180°C / 350°F for 7-15 min) until they are a light brown color. Roasting removes most of the green color!
  2. Option 2: Use the pistachios as is for a greener color.
  3. Use a (nut) chopper to grind the pistachios into a smooth paste. Add a little of the cream to help it smoothen out. You want to form a smooth paste to make a smooth ice cream.

Ice cream mix

  1. Mix the egg yolks, sugar, and corn starch in a bowl. Do not skip this step! Doing this helps preventing clumping of the corn starch and curdling of the egg yolk.
  2. Add milk to a pot and gently bring it to a boil.
  3. Slowly pour the hot milk in the egg yolk mixture while whisking continuously.
  4. Pour the mixture back in the pot and gently heat while whisking continuously. Continue to heat until it has thickened noticeably and formed a custard. Keep in mind that it will continue to thicken when it cools down.
  5. Take from the heat. Add the rest of the cream.
  6. Leave to cool down to room temperature or cool in the fridge for a couple of hours.

Finish and freeze

  1. Add the pistachio paste to the cooled-down ice cream mix.
  2. Use an ice cream machine to freeze the ice cream, follow the instructions of your machine.
  3. Enjoy your ice cream immediately, or leave it to harden in the freezer.

Notes

*Prefer an eggless version? Leave out the eggs and double the amount of corn starch (we discuss how that works here).

Resources

Scientific research done on the composition of pistachio nuts from various origins (very insightful!): Anthocyanins, chlorophylls and xantophylls in pistachio nuts of varying origins.

Analysis of Sicilian pistachio nuts: Carotenoid, chlorophyll and chlorophyll-derived compounds in pistachio kernels from Sicily.

Chlorophyll in pistachios from the Kitchn.

On Food and Cooking, from Harold McGee, version 2004

Two other articles I didn’t use as much are about the effect of roasting on the colour and presence of chlorophyll and an article describing the effects of ripeness of a pistachio on its properties.

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