The Food Lab: How to Cryo-Blanch Vegetables

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[Photographs: J. Kenji López-Alt]

Editor's Note: This article is adapted from my book, The Food Lab: Better Home Cooking Through Science. I hope you enjoy it. You can order the book here or on Amazon. Visit my personal website and sign up for the Food Lab newsletter to be the first to hear about my upcoming second book and live events.

Cryo-blanching is a technique that was developed by my friends Alex Talbot and Aki Kamozawa over at the blog Ideas in Food (they have a book of the same name). I've been following their work ever since I was a lowly line cook at Clio, the very restaurant where the couple honed their culinary chops. The technique sounds simple: rapidly freeze vegetables, then thaw and cook. But the concept is pretty brilliant, and, though I've recommended it in the past for getting the most flavor out of vegetables for gazpacho—which, of course, are blended up without heating—it's also a convenient way to precook certain vegetables before you sauté them.

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As I describe in more detail in my book, freezing vegetables actually causes many of the same reactions as blanching does, namely, helping cells to break down and internal gases to escape. As the vegetables freeze, ice crystals forming within their cells will puncture cell walls, weakening their structure. After thawing, what you end up with is a vegetable that is partially softened but still has bright, fresh flavor with a bit of crunch remaining. Eat them as is, and you won't be all that happy—their texture tends to be a little...flaccid. But if you sauté them after thawing to soften them just the slightest bit more, you'll end up with vegetables with perfect color, perfect texture, and the brightest, freshest flavor you've ever had from a sautéed vegetable.

The other beauty of the technique, of course, is that you can store your vegetables pretty much indefinitely in the freezer, requiring just a half hour or so to let them thaw at room temperature.

Preparing Vegetables for Cryo-Blanching

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Essential to good cryo-blanching is rapid freezing. This means two things: First, you must use vegetables with a small cross section, like green beans, asparagus, or peas, and second, you must freeze them rapidly in a single layer. If you've got a vacuum sealer (such as a FoodSaver), you can arrange your vegetables in a single layer in the bag before sealing them, then toss the bag directly into the freezer. Alternatively, lay your vegetables out in a single layer on a rimmed baking sheet and place them in the freezer, uncovered. Once they are completely frozen (give it a few hours to be safe), transfer them to a zipper-lock freezer bag, squeeze out any excess air, seal, and return to the freezer. They should be good for at least a few months and can be cooked directly from frozen.