Food Science: How Freeze Drying Works

Remember astronaut ice cream? Ever wonder how they managed to convert a creamy melty treat into a crumbly ice-cream-flavored block? As kids, we called it magic and left it at that. As adults, we're curious to get the real scoop ! (No pun intended...)

The goal of freeze-drying is to remove all the moisture from the food while leaving its basic structure intact. This increases its shelf-life, decreases its weight, and allows it to be reconstituted later without significant loss of taste, texture, or appearance.

We do this mechanically by first freezing the food so any liquid it has will form into solid ice crystals. Next, the pressure is decreased while the temperature is increased just slightly. This forces a process called sublimation, which means that the water will convert directly from ice into vapor without passing through its liquid phase. Fancy!

What's left behind is a very dry shell of the original food. If you looked at it under a microscope, you'd see a honeycomb structure left behind by the evaporating water. Tightly-sealed in an absolutely air-tight container, freeze-dried food will last for years. All it takes is a little water to make it edible again.

Freeze-drying has actually been around a lot longer than you might think. According to Harold McGee in On Food and Cooking, freeze-drying was first used by the native people of the Andes. A combination of dry sunny days, freezing nights, and high altitude meant that meat left out to cure would dehydrate while leaving the basic structure of the meat intact (unlike making jerky).

Incidentally, freeze-drying is different from dehydrating because dehydrating changes the food's original structure, affecting flavor and texture. Jerky and dried fruit can never look or taste like the original food again. Then again, astronauts and soldiers with Meal-Ready-to-Eat rations might argue that freeze-dried foods also taste nothing like the real stuff...

What's been your experience with freeze-dried foods?

(Image: Flickr member hyku licensed under Creative Commons)

Comments (7)

Astronaut ice cream....urrrppppph. They still sell dehydrated ice cream for backpackers. Kind of like gnawing on a sugared florist's oasis.

Some of the most satisfying freeze dried foods I've seen on the trail are from Knorr...soup mixes that can be combined with freeze dried rice and packaged chicken breast (don't know the brand, not freeze-dried but it doesn't require refrigeration.)

Knew some people that had a freeze dried coffee that was very, very good. From Europe. Would love to know where to find it.

I love freeze dried foods and astronaut ice cream! I still buy it whenever I see it; there's something about the textural change that I just love.

Trader Joe's sell freeze dried strawberries that are great. They also sell sliced freeze dried bananas and rambutan, which is a tropical fruit that I'd never heard of before; both are pretty good.

I also have a great childhood love of freeze the dried mini marshmallows that come in hot cocoa packets!

Oh, I used to love Astronaut Ice Cream! My dad used to bring some to my sister and I whenever he passed through an airport that sold it. Yeah, it was kind of awful, but we loved it!

http://www.abreadaday.com

FYI, Meals-Ready-to-Eat (MREs) aren't freeze-dried. They're essentially canned in thick foil packets, exactly like you see a lot of tuna in these days. Hey, I think they stole our idea :)

I think it'd make for a pretty entertaining column to have the Kitchn review a couple of MREs. They're better than you'd expect. On the low end (pork rib, beef ravioli, chicken w/noodles), they're somewhere between school lunch and Chef Boyardee, but on the high end (beef enchilada, spicy penne pasta) they're actually something I might choose to eat, which is saying a lot for a meal that's shelf-stable for a decade. And the desserts are a remarkable achievement of food science.

We freeze-dry for camping (there are whole cookbooks for this), and it actually turns out very well. Plus, the home-made kind avoids the massive sodium overload in lots of commercial freeze dried foods for backpackers!

Last week on Bizarre Foods (Andrew was in Houston), NASA shared a horrible secret with the world: they do not send ice cream up any more. In fact, they only sent it up one time in the 60's. Something about nobody liking it and having much better options available :)

I remember on my way to Algonquin Park with my dad for a backpacking trip a place we stopped at for supplies had cans of freeze dried water for sale.