How To Dry Food With the Sun

Drying Apricots in Southern California–early 20th century style.

Dehydration is one of my favorite food preservation techniques. Drying food concentrates flavor and is a traditional technique in our Mediterranean climate. Best of all, drying food is one of the best applications for low-tech solar power. In many places, you can simply set food out under cheesecloth to dry in the sun.

But there’s a catch to sun drying: humidity. Food dries best when temperatures are above 85º F and below 60% humidity. If you live in a desert, humidity isn’t a problem. But in most other places in North America it’s simply too moist to set food out under the sun. It will rot before it dries. In Los Angeles, due to the influence of the ocean, it’s slightly too humid most of the year for sun drying to work well.

But there’s an easy way to overcome humidity: convection, i.e. hot air rises. Most solar dehydrators take advantage of the passive movement of hot air to lower humidity enough to dry food. Here’s a couple of solar dehydrators that harness this simple principle to dry food without electricity:

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A DIY Whole House Fan

Our DIY whole house fan.

How hot is our unairconditioned, uninsulated old house? Kelly has temporarily banned bread baking and I’m thinking of opening my own Bikram hot yoga franchise.

But seriously, a few summers ago I decided to install a whole house fan. What’s a whole house fan? It’s a large fan, mounted in the ceiling, that pushes hot air into the attic while simultaneously drawing cool air in from the outside. You turn on a whole house fan when the air outside is cooler than the air inside the house, usually in the evening. It works best in climates that have hot days and cool nights–like Los Angeles or many other parts of the Southwest.

Diagram from Gear Hack.

Whole house fans are usually placed in a ceiling towards the middle of the house. For us that’s the hallway. Unfortunately, between the attic access door and the intake for the central heater, our hallway ceiling had no room to fit a standard whole house fan. And I’m cheap. So I decided to make a DIY version.

I picked up a shop type fan and installed it in a 3/4 inch piece of plywood cut to fit the attic door. It was a simple project and saved a lot of money. I think I spent around $30 for the fan and used a piece of scrap plywood. I added two handles to make it easier to remove the fan/door and access the attic. The final touch was to install an outlet in the attic wired to a switch hidden in a closet so that I can turn the fan on and off. When cooler weather comes around I simply swap out the attic fan for the normal attic door. Would a commercial whole house fan work better? Yes, but I try not to let perfection be the enemy of the good around here.

An attempt to use a bike pump as an air conditioner. Hot cat in background.

It’s still damn hot at Root Simple world headquarters during the day. So maybe I will open that combination bakery/Bikram yoga franchise where you can eat buns while you tone your buns.

Book Review: More Other Homes and Garbage Designs for Self-Sufficient Living

If I could have only one book on my zombie apocalypse bookshelf it would be this one. Though it has to be one of the worst book titles ever, More Other Homes and Garbage: Designs for Self-Sufficient Living, by Standford University professors, Jim Leckie, Gil Masters, Harry Whitehouse and Lily Young has everything you need to set up your off-grid compound. This book, first published in 1975 and revised in 1981, grew out of a heady period in appropriate technology research and DIY hippie experimentation that took place in the late 1960s and 1970s. In some ways it’s the rural version of the original urban homesteading book, The Integral Urban House: Self Reliant Living in the City.Both books, not coincidentally, share the same publisher.

Feeding the digestor on the homestead. An illustration from More Other Homes and Garbage.

More Other Homes and Garbage covers alternative architectural materials, passive cooling and heating, home power generation, solar water heating, methane digesters, sewage reuse and disposal, water supply, small scale agriculture and aquaculture. All topics are covered in great detail with, as is expected for a group of engineer/authors, lots of formulas and tables. While some material is out of date (Art Ludwig has taken greywater well beyond what’s in this book), most of the 374 pages of More Other Homes and Garbage are still very useful.

I especially like the can-do DIY tone of the introduction which describes a middle ground between “terminal pessimism” and “technophilic optimism.” What’s depressing, in fact, is that a lot of the topics in this book have not received much attention until very recently. The frivolous 80s and 90s were simply not the time for More Other Homes and Garbage. Thanks to the great recession, however, this book is relevant again. Get your copy before vengeful Mayan time travelers zap the interwebs in December.

Update July 31, 2012
A Root Simple reader, Lisa, pointed out that you can download this book for free here. Thanks Lisa! 

Sun Boxes: A Solar Powered Public Art Project

It’s not often that my unused music degree intersects with the topic of this blog, but I got an email from Craig Colorusso describing a neat, solar powered public art project that he’s touring the US with called Sun Boxes. From the description on his website:

Sun Boxes are an environment to enter and exit at will. It’s comprised of twenty speakers operating independently, each powered by the sun via solar panels. There is a different loop set to play a guitar note in each box continuously. These guitar notes collectively make a Bb chord. Because the loops are different in length, once the piece begins they continually overlap and the piece slowly evolves over time.

You can find out more about the project at www.sun-boxes.com. Make sure to listen to the recording of the boxes–I could listen for hours–the sound is at once hypnotic and deeply relaxing.

My Trip to Maker Faire


Getting ready for the earth oven workshop this weekend meant that I never got around to reporting on my trip to Maker Faire up in San Mateo on the 19th. I spoke in the low-tech “Homegrown” shed far away from the high powered tesla coil displays happening elsewhere. To add to the low tech/high tech irony, I was not able to use my PowerPoint and had to speak extemporaneously. This worked out for the better, as I was able to pull up a member of the audience to demonstrate her solar cooker–much more fun than showing pictures of solar cookers. And, after all, maybe it’s time we retire PowerPoint.

Some of the things I spotted at Maker Faire:

Long lines for the tiny house. I’ll review Lloyd Kahn’s awesome tiny house book later this week (he gave a talk just before me). Not sure what’s up with the white robe outfit in the foreground.

Also spotted: bamboo bikes!

Cornelia Hoskin, who curated the Homegrown Village part of Maker Faire, her husband and new bambino. Cornelia also runs homegrown.org.

Yes, there were paintings done by snails.

Solar popped popcorn.
A rep from Sweet Maria’s Coffee gave a great demo on all the ways you can roast your own coffee.

Expensive AK-47 toting garden gnomes.

And solar powered bikes. Not sure how this would work out on an LA street.

Someone in the Homegrown area was processing greywater in bulk containers planted with bamboo.

Overall I had a great time. It was a wee bit heavy on the robots and 3d printer gadgets but that’s to be expected. At least there were a few chickens present to balance out the proceedings. However, next year I’m coming with an overhead projector:

Our New Earth Oven and How We Built It

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The almost completed horno–waiting for its final plaster coat in a few weeks.

Kurt Gardella and Ben Loescher taught an amazing earth oven workshop at our house this weekend. Keep your eye out for classes these guys offer if you are interested in earth ovens, adobe houses or earth plasters and finishes. Contact information is below. Here I thought I’d briefly describe the process with a few pictures.

One of the nice things about this oven is that it was almost free. The only two expenses were for sand and some bags of gravel. The clay we mined from the backyard and almost everything else was scavenged. Total cost was less than $200 and most of that was the delivery charge on the sand. If I’d had a pickup truck I could have loaded the sand myself for much less.

In our backyard the ground beneath the top level of organic matter is almost pure clay. I found that a 50/50 sand/mined clay mix with just a bit of chopped straw thrown in for stability seemed to be about right for making adobe bricks. There’s no recipe for building with earth. You have to get to know the clay content of the soil you’re working with and test how much sand to add to it to make a solid brick. Ben and I made quite a few test bricks to come to this formula. Then I made 100 adobe bricks using just a simple wooden frame as a mold.

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A simple gravel pad.

To build the horno we started with a gravel foundation held within a border of treated wood. The base of the oven was made from adobe bricks that I made over the past few months and cured in the sun. I’m a big believer in adobe. Making so many bricks familiarized me with the soil I was working with and put me in touch with the original building material of the American Southwest.Though we only used half of those bricks, I’m happy to have some left over for other projects in the backyard I’d like to try. Also, after all of our lead trauma, its great to put the soil from our yard to good use. This was a healing project in some ways.

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Base nearing completion.

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Bottles acting as an insulation layer. We should have had Sierra Nevada sponsor this oven!

Once the base was built we filled it with leftover gravel and adobe bricks. The top layer of the base is a mix of clay, straw and beer bottles. This acts as an insulation layer to keep the base from soaking up the heat of the oven.

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Laying the oven floor.

The floor of the oven is made of standard red bricks set in a thin layer of sand. Fire brick is recommended for this application, but in Kurt’s experience it’s not really necessary. Plus fire bricks are expensive and we had a lot of red bricks laying around that we wanted to use. Again, we wanted to build this oven without having to buy a lot of materials.

Next we sculpted the shape of the oven in wet sand. This form will allow us to shape the clay dome and will be scooped out later.

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Kurt points at the completed sand form.
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Packing on the thermal layer.

With the base completed, on day two, we started to work on the dome. We packed a four inch thermal layer of more clay, sand and straw over the sand. Next came a insulation layer with yet more clay, sand and a lot more straw. The dome layers are cob–stiff and very difficult to mix. I think if I were building a house I’d use adobe bricks which can be made with a concrete mixer. At the end of the day we scored the dome to fit the door.

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Carefully cutting open the door. This is the completed thermal layer. The scratches in the clay will help the next layer adhere.
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Starting the insulation layer over the thermal layer.

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Stinky fermented cactus juice is added to give strength to the final plaster coat.

On the third day Kurt cut open the door hole and carefully removed some of the sand from the dome. In a dry climate all the sand might have come out on that day, but we decided that the dome was still soft and decided to leave most of the sand in for another week, just to be extra safe.

Next we mixed a coat of earth plaster–again, basically the same ratio of sand, clay and straw we used for the adobe bricks–with the addition of two stabilizers to help repel water: fermented prickly pear juice and wheat paste. The prickly pear juice we made by chopping up some cactus pads from our front yard, adding water and letting it sit in a five gallon bucket. The finished material is lurid green, slimy, and stinks to high heaven. The wheat paste is just flour and water.

We’re going to let the oven dry for a few weeks before applying the final earth plaster layer. That one will be as smooth as we can make it. And we’ll need to sand the dome opening to fit the door. Once that is done, we wait some more. The oven can’t be used until it is completely dry, which should take about a month.

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Applying the first of three earth plaster coats.

I find earth building, while labor intensive, very satisfying and meditative. It’s also something that is much better to do in a group. So thanks again to all who helped helped: Kurt, Ben, Brian, Jenny, Connie, Laurie and Leslie. We’ll post some more pictures when the oven gets its final coat of plaster.

For more resources and classes on how to build with earth see:

Three Days of Earth Oven Building Compressed Into a Short Video

We just finished a three day earth oven workshop taught by Kurt Gardella and Ben Loescher. Many thanks to all who participated: Laurie, Brian, Leslie, Jenny and Connie.We’ve got to let the oven dry for a few weeks before we put on the final coat. But it’s basically finished. The base is made with traditional adobe bricks and the dome is cob.

Don’t worry, we’ll explain the process in future blog posts. Right now we’re too exhausted to write about it. In the meantime, please enjoy our highly compressed video version of the past three days.

A Rocket Stove Made From a Five Gallon Metal Bucket

The principle behind a rocket stove is simple–rather than cooking on an open fire, you burn wood in an insulated chimney. Rocket stoves are highly efficient and easy to make. They run on twigs, so you can avoid cutting down a whole tree just to cook dinner.

We’ve had a rocket stove made out of brick in our backyard for several years. The post we wrote on it in 2007 is–oddly–the most frequently searched post on this site. I figured that since there was so much interest in the topic it would be good to offer one that didn’t require masonry work. Better yet, I figured that it should be portable, so I made it out of a five gallon steel paint bucket. (eta: for your googling pleasure, it seems retailers call these cans “steel pails” rather than buckets). The project took less than an hour to complete and I’m very pleased with the final result. We created a pdf with full instructions that you can download at the Internet Archive. What follows are some photos showing the building process:

Using a piece of 4″ vent pipe and a 90º elbow, I made the chimney. See the pdf for the exact dimensions.

I traced the outline of the vent pipe on to the lid of the bucket and cut this hole out with a jig saw. Tin snips would also have worked.

Using the vent pipe as a guide again, I cut out a 4″ hole near the bottom of the bucket.

I used one part clay (harvested from the yard) to six parts vermiculite as my insulation material. Mixed with water, the clay holds the vermiculite together. I could also have used dry wood ash, but I had the vermiculite and clay on hand so that’s what I went with.

With the vent pipe in place, I packed the insulation into the bucket and let it dry for a few days before putting the lid on.

I found a barbecue grill at Home Depot that rests on the top of the bucket to support a pot.

Next you want to get yourself a tin can, take off both ends and open it up with tin snips. Cut a piece to serve as a shelf in the mouth of the pipe. It should be about 4″ long–so it sits forward in the mouth of the vent. The rear part of the vent, where the fire burns, is open. The twigs rest on top of the shelf, the lower half is for drawing air.

The last step was to add the new Root Simple stencil to the back.

Some fire tips from the little lady, our resident pyro:

A rocket stove isn’t like a campfire–you don’t throw on a big log and kick back. Cooking on it is intense and concentrated, best suited for boiling or frying. The best fuel source is twigs, small ones–I prefer pencil-sized twigs, and I never try to burn anything thicker than a finger.

To start a fire just shove some paper or other tinder under the shelf toward the back of vent. Lay some very thin twigs, pine needles or other combustibles on the shelf. Light the paper and watch it go. Start adding larger twigs to establish the fire. Of course, twigs burn fast and hot, so you have to keep adding more fuel. Also, the twig are burning from the back (the fire is concentrated in the bend) so as the fire consumes the sticks, you just keep shoving the unburned parts to the rear.

There’s a balance between choking the vent with too much wood and having too sparse a fire. After a few minutes of playing with it you’ll get the hang of things. If you’re doing it right, there should be no smoke, or almost none. These things burn clean.

Let us know if you like the pdf and if you would like to see more similar instruction sheets (maybe in an ebook format) of these types of projects. There’s also a good book on using rocket stoves as heaters:  Rocket Mass Heaters: Superefficient Woodstoves YOU Can Build by Ianto Evans and Leslie Jackson.

The Chinese Wheelbarrow

From the very cool Low-tech Magazine, the Chinese wheelbarrow:

The Chinese wheelbarrow – which was driven by human labour, beasts of burden and wind power – was of a different design than its European counterpart. By placing a large wheel in the middle of the vehicle instead of a smaller wheel in front, one could easily carry three to six times as much weight than if using a European wheelbarrow.

 Read the rest here. So who will be the first to make one of these with an old bicycle wheel?

Low Tech Solar Heating with a Thermosyphon Collector

Yet another great post from the folks at Build It Solar: a simple and low tech solar heating system called a thermosyphon collector mounted in the wall of a garage. It uses the same principle as the solar dehydrator we have on our garage roof–basically it’s just some clear plastic and a heat collector made out of black window screen. If your climate is cold and sunny (think Colorado) this would work nicely.

Read the post to see a review of its performance over the past nine years here.