DIY Freeze Dry and Dehydrator

Backpacking Food Tip #2: DIY Freeze Dry and Dehydrator

Most of the shelf backpacking foods tend to fall into two categories: dehydrated or freeze-dried. Either way, the water has been effectively removed from the food, making it less dense (lighter weight) and sometimes significantly smaller (depending on the food). So, water-less food is the way to go, standard operating procedure, for most backpackers and backpacking trips. While I prefer fresh food, every trip is going to involve something that I need to add water too, but usually from the store, like a pudding mix or red beans and rice mix (I’ll talk about them later, no doubt). So, the real topic here is getting away from the prepackaged backpacking foods that are, unfortunately, quite expensive, by using a DIY method.

Today’s entry is the DIY Freeze Dry and DIY Dehydrator. If you have these two skills, you can literally bring anything into the wilderness with you and make it lighter and more compact from the magic of water loss. So, whatever your cooking or packing skills are, pick up these home skills as needed.

So we’ll use chili as an example. Chili is delicious on the trail, and you can usually find some dehydrated boxes of chili beans and spices in the supermarket. What these lack are three things: water, tomato paste, and meat. (If you’re a vegetarian, bear with me. You can do this with tofu or the fake ground beef substitute in the veggie section by the produce. It’s just an exercise.) Those chili kits serve four on the trail nicely. A particularly good one is called Darn Good Chili, and it is. Divvy it in half for a duo. It does leave you a little bit hungry though, so you want to add meat or make some biscuits (that will come later too). We’re going the meat chili route.

If you were making this at home, you’d probably pick up a pound of chuck and a can of tomato paste for the chili kit. The pound of chuck in my store is going for about $4.00 a pound, rounding up. It’s heavy and bulky, so chuck is not a good trail option. Cans also are horrible to deal with in the back country – you have to clean them, and stow them, and they don’t get smaller. Backpackers often seek out the rarer alternate form of tomato paste in a tube, because it’s less messy and lighter (usually). The tubes in the supermarket are rather gourmet, so I will turn to a neutral but like minded source for pricing, the General Grocery page at Packit Gourmet, who makes food kits for food lovers. I like their schtick, but they are pricey.

At Packit Gourmet, I can get 2 oz of freeze dried ground beef for $9.99, which turns into 4 oz when rehydrated. I can also get a tube of paste for $4.99. The meat is pretty much a single person’s serving. That means, to rock my trail group’s socks off, I would need to buy four orders of 2 oz to get a full pound of meat, and spend $39.96 to do it. Meanwhile, the can of tomato paste I can get for $1.50, probably cheaper if I shop around. The ones on the shelf are usually 6-8 oz, and the tube stuff really isn’t that much more concentrated and is about 4.5 oz – they sort of equal out, so don’t worry.

So priced as such, I’d spend $44.95 for the backpacking versions verses $5.50 for the regular stuff. In my book, that’s just not cool. Ah, but what about the time and effort you say? Does that make up for it? Not really. Pick a day when you have some time at home, like to do laundry, or an evening where it’s an at home movie night, and your time is spent doing fun things and not watching the water leave your food. Not that laundry is as fun as a movie, but you get my drift, right?

DIY Freeze Dry

Dry ice at supermarkets and some other supply stores generally costs only $1 a pound. All you need is a cooler, and some left over plastic containers – or even ziploc freezer bags. It takes a couple of days, but if you try not to open the cooler, it works just fine.

You need about an equivalent amount of dry ice to your food, so here we need one pound to freeze dry our chuck. You can get more if you want to be sure. It works by sublimation, the process by which water turns directly into vapor without heating up to that silly steam phase of existence.

First cook the chuck and let it cool. Protect the chuck from the dry ice by using the freezer bags or layer it with it in the plastic containers using paper plates (it won’t stick to the paper). If you use the plastic, poke some holes. The whole point is to give the water an exit and let the dry ice vapor do it’s magic. Make sure the chuck is spread out into chunks so it will fall apart easily after freeze-drying.

Pop that into a cooler for a few days – you may need to crack it open every so often to let the vapor out (or put a towel under the lid to prop it open). Over time, the water will sublimate and leave the chuck behind. This can take several days, so you can pull out a test “bite” to see how it reacts when thawed. It should be shelf stable and somewhat hard/soft (not one way or the other). It won’t turn black or react with air, but it will rehydrate in water and regain it’s springy chuck-like qualities. Food-like qualities.

Bottom line: It might take some experimentation, but you can pretty much throw dry-ice and food into a cooler and get dehydrated food.

DIY Dehydrator

Dehydrators are also expensive, but at least dehydrated food is cheaper than freeze dried food (see any $1 rice-a-roni sale). There are a lot of DIY backpackers who very much insist on getting a machine to do this, but I bet you already have one. It’s called an oven.

Like with the DIY Freeze Drier, you need a place for water vapor to go, so you’ll need a towel or potholder to prop open your oven door, which makes this a great winter time or evening activity. Turn your oven on it’s lowest setting, usually 150-200 degrees F, put the food you wish to dehydrate in the oven on a tray, put the towel in the door (turn off your oven light if you can, here, or it may stay on) and leave your food alone for hours. Here’s what to do for our tomato paste:

High amounts of surface area is key for the water vapor to escape the paste, so you can’t just pop in an opened can. It won’t work. Get some parchment paper because it will peel off easily from that, $3. Cover your tray or a cookie sheet, or pan or whatever with a layer of parchment. Spread your paste over the parchment with a spoon or spatula so it’s thin as possible.

I like making “columns” so I can divide the paste up if I need to. Only need half the can for a recipe? Maybe you’re only a duo and only need half the chili? Or maybe you need some other arcane fraction for a recipe in the future? Lay out your paste accordingly. Divvy it into sections – one quarter in a square here, or halves. Leave a little bit of blank parchment in between and you have an easy way to visually divide your paste.

Pop the tray into your low-setting towel-doored oven. If your oven can do this, set it to Convect. It helps circulate out the vapor. Check it in about two hours, and you will see the progress. You can touch it at this point and feel the progress too. Little droplets of water will be forming on top of the paste – the paste will be sweating it out. It usually takes about 3 or 4 hours to do tomato paste, which is great for dinner-and-a-movie night at home. When you’re done for the night, take the tray out, and see if the paste has stopped sweating. It might still be a little sticky, but it should not be moist. You can let it dry on the counter overnight and just go to bed. That’s it.

Bottom line: A little prep-time, a towel, and your favorite James Bond movie combine to make packable tomato jerky.

Alternate method: This is a little dangerous with more liquid foods, and very dangerous with sticky foods, and I don’t think I would ever chance it in our Mustang, Grace, but you can indeed dehydrate your foods on the dashboard of a car. It’s like a little greenhouse. Just crack your windows and put your tray on your dash. I kid you not. The kids at our school made fruit leather that way. It takes all (school) day, but it’s brilliant. Dudes, are you listening? YOU CAN USE YOUR CAR. IT’S DUDE FOOD. (I’m looking at you, Quinn!)

So there it is. If you have a little time and want to expand your trail recipes, or just want to lighten the recipes you have, you can very easily put together a DIY Dehydrator or a DIY Freeze Drier. See what seems to fit your style best, or what you want to try. The DIY Dehydrator is a little more sure fire the first time around, but the bottom, bottom line is this:

Why should I spend $40 more for food I can alter in my own kitchen while watching Pierce Brosnan find yet another way for Sean Bean to die on screen like I did last night???

(That and playing with dry ice with gloves makes me feel like a mad scientist. You?)

Cheers, and happy eating!


~ by glasslajora on January 19, 2013.

4 Responses to “DIY Freeze Dry and Dehydrator”

  1. Thanks so much! My Husband, and I are trying the Ground Chuck with dry ice tonight! I so hope it works out, because I have a list of stuff I would like to try!

    • Awesome! I hope it works well for you.

      I also heard another method of dehydration using a box fan and paper fiber heater filters. Okay, by “heard” I mean “saw it on a re-run of Alton Brown’s show ‘Good Eats.'” He put food in the grooves in the filters and strapped them onto the fan with bungie cords. Anyways, he had a pretty good argument as to why cold preservation techniques, like freeze drying (what you’re going to try!) and cold dehydration (his DIY method) are better at preserving the taste of food than hot methods like ovens or traditional dehydrator appliances. Also, it’s pretty dang economical for the electricity spent, which is good for the long term (unlike the oven). So, I have a fan, and got some filters, so I hope to try this soon and add it onto the blog.

  2. I have two questions. The first is have you attempted to freeze dry with this method but instead of lifting the lid to let out the vapor from sublimation, using a a desiccant like silica in a jar to help with the process? My second question is have you figured out what your shelf life is for the freeze dried food you have done? If this works well I could really make a ton of survival / camping meals. Thanks!

    • Hi Andrew!

      I haven’t tried it with a desiccant, but I would love to see the results. It makes sense that it would work, but I wonder if there’s an easy way to calculate how much you would need since you are starting with a very moisture rich item. How much silica (or other) would be needed? Certainly anything that helps draw moisture away can’t hurt, though. It’s a great idea.

      I did, however, have a blast putting together an Alton Brown style DIY box fan dehydrator (basically an air flow freeze dryer) and that worked amazingly well, like brilliantly well. AMAZEBALLS well. His videos are available online, but I shall have to get off my butt and post the results. We made it and took the results backpacking right after, and it was just too much fun to strap together.

      The short answer for shelf life is about a year, depending, and I’ll try to explain that here as a full reply of what I know or have gathered over time. If I were camping, there’s no worries at all. If I were making a kit for the home or similar (like out here in California we have Earthquake kits), I’d replace the food yearly, but I’d cook the food coming out of it if it still looked fine. It’s just good to rotate and keep those kits fresh.

      Shelf life seems entirely dependent on the amount of moisture successfully drawn away, and storage conditions. The more dehydrated and mummified your food is, the better it will last. Not that a shoddy job is okay, but If I’m backpacking next week, it’s okay to be a little imperfect on a batch. If it’s for a survival or long term food kit, I would want to leave the method going a while longer. If this is ideal, you’ve got a year for most foods before we check them.

      From what I gather, fruit, like the tomato paste, becomes leathery at 20-25% moisture, and vegetables become brittle at around 5-10%, which is good for long term storage. I don’t know if the percents are right, it would require some science experiments and burning things (fun!) but leather for sauces or fruit spreads and the ability to break/snap produce is where you want them. The sauces with their higher moisture content are not as good candidates for long term storage, because they could go, but if you store them fine, they could still be good for a year. If your conditions are not as good, it might be closer to half a year, or it’ll become that funny jar of jam in the back of the fridge you swore was new, but, alas, is covered in colonies.

      I know that storage conditions, like oxygen, light, and heat exposure will effect food. There are some old wives tales that are tossed around on survival websites about temp. For example, modernsurvivalblog says each drop of 10°F doubles the shelf life, but then you’d want to be freezing your freeze dried or dehydrated food which defeats the purpose. From what I gathered from other sites, this came from a USDA study about seeds, which are more sensitive (looking to gestate, or die) than dehydrated foods, so I doubt the claim is that dramatic when it comes to a freeze dried carrot. The bottom line however does remain that dried food should be kept cool, dry, and ideally 50- 70°F. The point is not to go hot (bacterial growth) nor cold (breaks the cells). But especially hot; you can still eat the frozen stuff even if it’s not pretty.

      The emergency kits I’ve seen do a similar thing, check after X-many years, 1-5 usually, or restock, because that’s their guarantee. You could probably eat it, but they can’t guarantee it. Heck, even my scientist fiancé has to replace the water they use at his lab, just like any other chemical, and we know that doesn’t go stale – but the packaging could, or other bad things could’ve happened, or at least it got them to check on the materials, and that’s the point. Mountain House has some absurd twenty-five year shelf life claim for cans (in case you’re stocking a fallout shelter?) and ten years for pouches they pack things very nicely in the shiny bags which must play a part in it. Their tech is very good, but I still wouldn’t leave it out in the open desert heat for twenty-five years and expect a delicious meal. Even if I was including premade/prepackaged goodies like Mountain House, I’d check them yearly, and maybe swap them after half their shelf life, when there are probably better flavors and better tech to replace them with anyways.

      Survival kits get the win on the packaging though, as they can take time, like the Mountain House Can withstands time. If you were diligent in packaging, you could probably extend the shelf life out a lot father than the year marker for such a kit to put it somewhere where there are more variables, like a car or boat, or stash in a cabin or other location you don’t often go to. Just avoid the moisture rich leathers/sauces!

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