

Solar Food Dehydration - no electrical power needed





Once you have gotten into gardening's seasonal rhythms, you will soon have to find a way to deal with surplus produce. Planning for extra beyond your daily fresh meals leaves foods for later consumption. But some preservation is necessary to turn this bounty into something nutritious and delectable months from now. If the crop does not lend itself to long term live storage, then some food processing will come into play. Many immediately leap to the idea of canning but our preference, in our nutrient and energy saving hierarchy, is food drying, or dehydration. Solar-dried foods do not require fossil-fueled energy inputs to preserve them or store them, unlike freezing. No specialized canning equipment or fuel needed. No electricity required, only sunlight from a safe nuclear power source about 93 million miles away! And a tightly sealed glass jar in a cool, dark place will do for storage. Reducing the amount of energy you use for food storage will further shrink the carbon footprint that you have already reduced by eating locally, growing your food biologically, and replacing your fossil-fueled tools with something more task-appropriate (like a garden fork).







A Solar Food Dryer That Actually Works (even in the humid upper-Midwest)



First, some photographs and a drawing of our solar food dryer design so you can get an overview of how it is built:







This is our finished solar dryer, 12 by 4 feet, with 2-by-2 foot stainless steel screens framed in 2-by-2 inch cedar, and three 4-by-4 foot heat-generating solar collector panels (one is opened for the photo). Sunlight shines through the clear glazing cover, which protects the collector from the elements and helps to create an insulating airspace. Moving downward, it then hits a black-painted aluminum sheet, heating the metal. The back side of the black aluminum re-radiates infrared heat into the food below, causing the food to heat internally instead of only on its surface, as with convective dryers that move heated air around the food. Convective dryers are more like likely to cause "case hardening", where the surface of the food dries while the interior stays wet. In our design foods quickly lose moisture while keeping nutrient-robbing direct sunlight off the food itself. Moisture given off by the heated food passively flows out under the screens and up the sloped air channels under the screens. And the galvanized steel roofing, with raised ribs forming the air channels, reflects heat back up toward the food, improving overall efficiency. It's not the prettiest dryer, not the most compact, and not the cheapest. It simply does what it is intended to do very well by following the rule I always tell people, "You can't fight physics!"





Solar dryers are a different breed - design accordingly!



A solar food dryer works only when the sun shines so your design MUST take full advantage of the time when the sun is up!



This photo shows the internal temperatures of three solar dryers over a two day period, in May, in north-central Minnesota, with each drying five pounds of apple slices. Two of the dryers were "box types", emulating the stacked tray design of a typical electric dryer. One had a separate collector like an "Appalachian" dryer and the other was a simpler "black box" type. And the third one, shown using the grey line (Kent), was of our flat radiant design. On the first day the flat dryer temperature reached nearly what you would find in a commercial electric dryer, then it cooled way down at night. There was much less temperature variation in the other designs. On the second day, with less moisture in the apples, the temperature in our dryer design got much warmer and the dried food got well below ambient temperature at night. In other words, it takes full advantage of the sun and preserves the food overnight.







And this photo tracks relative humidity levels in each dryer. You can see how our design really draws out humidity when the sun shines while the other dryers really didn't do very much. The odd peak of humidity, at the end of the second night in our design, is from ambient air, not the apples (which were already dry enough), due to dryer temperatures getting well below the dew point on the second night. Our flat radiant design really removes moisture during daytime, enough to let the produce "coast" overnight in the dryer. Other design simply are less efficient.









More design details



This photo shows a side view of a model solar dryer (only 2 by 2 feet) that we show folks for construction details. You can see one of the loose-pin hinges connecting the solar collector to the base on the north and south sides. The stainless steel food screen is at the bottom of the removable, 2"x2" cedar-rimmed tray in the middle of the stack. And you can see the air space formed below it by the ribs in the galvanized roofing. More below!







Above you can see the sketch in our book that shows all of the dryer's layers with a breakdown of which elements are in each layer. In reality, when you build one of these it will no doubt be wider than this 2-foot model, so you will need additional hinges to keep it steady when it is opened.



The top (cover) layer, which does the work of solar collection, uses either flat "Kalwall"-brand fiberglass reinforced polyester glazing or some other clear glazing. We currently are using corrugated polycarbonate and find it to be the most durable option but polycarbonate twinwall can also be used (not needed for its insulating qualities so thinner is best). Other types of glazing are available that may be recycled or cost less and work as well. You will find more to read about these below. The black metal sheet could be either aluminum or steel.



The food trays could be framed with wood, aluminum, or something else, as long as they don't off-gas toxic fumes when hot. We use woven stainless steel screens for the surfaces contacting food as it's the most food-safe option around and is both easy to clean and remarkably durable.



The airspace here is created by the corrugations in the steel roofing below it. The airspace allows warm, moist, upward-moving air from the food trays to exit the dryer on the upper side (north side in the northern hemisphere, south side in the southern). Other options could include a flat metal base with 1-inch wooden spacers running north-south above it to make the airspace. Corrugated roofing with multiple "waves" also works, but its abundance of contact points at each rib creates a "hot spot" where foods can sometimes overheat.









Walk Radiant Dryer

Appalachian Dryer

Mother Earth Dryer

Black Barrel Dryer

food dries itself by absorbing radiant heat

food is dried on its surface

food is dried on its surface food is dried on its surface requires no solar tracking

requires periodic tracking

requires periodic tracking

requires no solar tracking works well when humid or partly cloudy

needs full sun & low humidity

needs full sun

needs full sun & low humidity

screens can be fully loaded

screens should be lightly loaded

higher loading slows drying

screens should be lightly loaded

food not exposed to sunlight

food not exposed to sunlight

food exposed to UV-A

food not exposed to sunlight

passive design - no moving parts

some use an added fan

passive design

passive design



But why build it this way?

Among the many inquiries we get for our stainless steel food drying screens we often find folks building the ubiquitous "Appalachian box" solar dryer. It is the knee-jerk design response for nearly every solar enthusiast wanting to avoid electric dryers since it seems like such an intuitively correct choice. This design requires periodic sun-tracking during the day, its many stacked layers of wet food require lots of air flow, the screens have to be removed from the dryer when it is not heating since the food will easily get moldy, and since its ratio of collector area to screen area is so much lower, it is far slower when drying anything but thin greens. Since proper airflow is critical to the design, construction must be precise and air-tight. Still, people persist in building it since it is found so frequently in web searches and because it emulates the familiar design of most electric, box-type, convective dryers.



There is simply no way that a convective box-type dryer can be as efficient as a radiant dryer. Air is not dense enough to either hold or conduct very much heat. It is far more efficient to use radiant infrared energy to penetrate and heat the food internally, forcing moisture out from deep within the food rather than simply slow-drying the surface. Think about forced-air heating versus a wood-stove in a home. The wood-stove radiates heat directly onto your clothing and into your skin, making you feel warm even at a distance. The furnace blows warm air around the room but the movement of air actually causes moisture on your skin to slowly evaporate, creating a slight cooling sensation that fights the warm air. The same thing happens in a box-type solar dryer. The sun heats some air, but the act of moving often humid air through the food is counterproductive and not much heat actually gets transferred. In our "indirect solar radiant" design the only convection occurs beneath the food, under the screens, where it gently carries off humidity. The food itself stays warmer, it dries from the inside, not just the surface, it's all in the path of radiant heating, and this combines to speed moisture loss, even on less than optimal, partly cloudy drying days. While some foods will "case harden" (dry more quickly on their surface first) even using our design (celery pieces and raspberries are notorious for this), they are less likely to do so.



Another overly-hyped dryer design, endorsed by Mother Earth News, is the hybrid radiant-convective box design from Eben Fodor. It uses a couple of stacked screens placed above a black metal collector sheet. As you load more food on the screens more of the solar collector is shaded, cooling the airflow. That is exactly backwards from the ideal design. Any food that drips will do so on the collector sheet, requiring frequent cleaning and possible repainting. And since the screens are stacked the unit has all of the construction and usage drawbacks of the box dryers.



And yet another hybrid radiant-convective design we have used is the "black barrel" design, where a black-painted steel barrel is suspended horizontally inside a cylinder of plastic glazing. The barrel holds a stack of screens and there is a solar chimney on top to remove warm, moist air while cool air enters at the bottom. On the plus side, the design is passive, it keeps sunlight off the food, and it does not need solar tracking during the day. But on the minus side it simply doesn't dry stacked screens of food adequately.



A possibly confusing notion is our use of the terms "upper" and "lower" when referring to dryer screens. We place two 2-by-2 foot screens side-by-side, in the north-south axis, under the collector. Since the screens are on a slight slope, we call the higher one the "upper" screen, and food placed on it gets slightly hotter than the lower screen, due to heat rising under the screens. The screens are NEVER STACKED as they are in a box-type dryer. Stacking screens only works in box dryers because they rely on air movement rather than the direct radiant heating of a single layer of food.



And if you would like to see a series of photos showing another version of this dryer, built by folks in Virginia (latitude 38N), just Click Here. You can see what higher sun angles and a taller dryer (which gets hotter at the top) due to some thinly-sliced peaches when you don't keep an eye on them. Don't panic! Every dimension and aspect of the design can be changed to suit most any climate, altitude, or latitude. Or you can just slice the peaches thicker!



More photographs of our dryer with food in it are found by scrolling down nearer the bottom of the page.





Free PDF with Photos of a Dryer Building Workshop:



For those of you who would like to get a better grasp of the dryer building process, we have a free, 10-page PDF download of a recent (2011) solar dryer building workshop showing lots of details not previously posted. We built a total of 15 dryers in 7 hours, including lunch, with a crew of 20 new dryer enthusiasts. Check it out!



The information in the paragraphs below is from workshops presented by Larisa every year at the Midwest Renewable Energy Fair. If you missed the fair, or didn't get a handout, the printed materials are here as a PDF, along with some extra visual and textual elaboration below. Topics covered at the workshops included the solar food dryer we designed, steam-canning, steam-juicing, and root-cellaring.









The Walk Solar Food Dehydrator - How it Came About and How it Works

(our workshop handout)



Over the years I've tried about every solar dryer design imaginable. The only common factor in all those attempts was their very limited usefulness here in the humid upper Midwest. None of them could reliably turn food into a non-moldy finished product, unlike the many successful electric models I had built for myself and friends. Some didn't work at all if not tracked periodically during the day. Others were simply too slow, exposed the food to sunlight, or relied on electric "backup" at night. It was with this background that the "idea light" came on in my head.



The Hot Tin Roof Theory



One day (in 1985) I needed to dry a bunch of greens and the current solar dryer was full (a couple of handfuls was all it could handle). I had an old window screen laying around and a corrugated metal roof built over our old mobile home. Using a ladder to get on the roof, I put the screen down first and put the food on it. I wanted to warm the food while keeping the sunlight out so I covered it with a piece of black cloth. Then to keep everything from blowing away or being bothered by flies, I covered it with the storm window that was laying around with the screen.



Later that afternoon I thought I'd check up on the experiment. The greens in the old dryer were still quite limp so I crawled up the ladder to take a look at the stuff on the roof. Much to my surprise, the roof-top greens were crispy dry! It looked like I had finally stumbled on something that worked. I tried several other foods on the roof before I was convinced enough of the design to build a unit at ground level for easier access.



Basic Design Principles



I found through experimenting that the primary ingredients for this idea were:

glazing (glass or greenhouse plastics) to seal out rain and raise interior temperatures



black surface over the food (fabric or metal) to keep sunlight off the food



food-safe screen to hold the food and allow moisture movement outward



corrugated, galvanized, metal roofing tilted for airflow and aimed toward the sun So this is the combination of design factors that also met the criteria of what I thought would be the ideal solar dryer:

utilizes passive solar energy



has no moving parts



no tracking required to follow the sun



food not exposed to sunlight *



spacious enough to accommodate large pickings



moderate temperatures to dry quickly but not overheat



easy to use and clean

absolutely must work reliably, even in high humidity



not necessary to remove partially dry food from the dryer overnight **



stable in windy locations



mostly "critter" and bug-proof (if there are bears in your area all bets are off!) *

*The only exception to the "no sunlight" rule that we know of is mushrooms. Some species of mushrooms can be dried using sunlight exposed directly (no glass or plastic shielding them from UV light) on the spore side to produce loads of extra vitamin D. Lentinus (shiitake) mushrooms can have 10 times or more their normal, already high levels, making them almost a supplement instead of a food, and making vitamin D overdose a possibility among mushroom lovers! Check out Paul Stamets' books on mushroom culture for more details.



** There are a couple of exceptions depending on where you are located and what you are attempting to dry. If you have bears around and they are hungry (when aren't they?) you either need some MAJOR fencing or you should just bring the "bear bait" indoors. And if you are drying something intensely sweet, ants may discover your food by climbing up the dryer legs. We suggest either applying ant-repellents such as orange or peppermint essential oil to the dryer legs, or making "moats" using cut-off plastic jug tops, trimmed to fit the neck around each leg, mounted upside-down, caulked with silicone, then filled with water.





Building the Radiant Super Dryer:



Using the basic principles and design criteria established from our experimentation, we built a 4-by-12 foot, waist-high "shed". The metal roofing on this shed has corrugations that run north to south. The roof angle is approximately 12-15 degrees from horizontal and slopes toward the south (in the northern hemisphere). This gives enough slant so the warm air will rise but not so much that the food will slide downhill. The mini "shed" space underneath can be used to store firewood or garden accessories. The 4-foot width enables food to be reached from either side yet is wide enough to achieve sufficient hot air flow. The legs are 2-by-2 inch treated wood and stick into the ground about 6-12 inches. Metal fence T-posts attached to the wooden frame with U-bolts are a good alternative if you don't like treated wood. Additional leg bracing may be necessary if your dryer is large. A good "starter" size is 4 by 4 feet with four 2-by-2 foot trays. You can make more modules of this size later if you need to add capacity.



Our dryer holds twelve 2-by-2 foot screens made from mitered cedar 2-by-2's, with a deck screw in each corner. The lower inside edge of the frame is cut away so that the screen is recessed a bit from the outside edge. This eliminates the possibility of screen edges snagging clothes when you lean against the dryer. The screen is stainless steel which, although costly, is easy to clean, provides a non-toxic surface for the food, and should last a lifetime. A bead of high-temp, food-grade, silicone caulk (any of the "100% silicone" caulks without added "mildew resistance" biocides will do) keeps food particles from getting stuck between the wood frame and the screen. A less costly but controversial screen option is "food-grade polypropylene" screening (available, among other sources, from Dryit.com). You will need to provide support under this material to prevent sagging. You could use galvanized metal fence wire or hardware cloth for this as the food would not come into direct contact with the metal. My original experiments used fiberglass window screen, but I have since discovered that it is coated with polyvinyl chloride that is stabilized with several substances, one of which may be lead. Please do not place food in direct contact with any material that is not absolutely food safe. This would include plastic garbage bags/cans, galvanized metal, and aluminum screening or cookware.



And while some plastics (polypropylene, HDPE, nylon) are advertised as "food-safe" that may be just a self-serving boast. With just what IS currently known about xenoestrogens and plastics we prefer the metal. Some bloggers, without an actual basis in data, have questioned the purity of Chinese-made stainless steel screening, implying that it might contain some impurities. Metallurgically, type 304 or 316 stainless steel is made to a strict formula. No matter which chemical impurities, (found in tiny amounts), might possibly react with your food on a metal screen, at least you know that they might actually be necessary as an enzyme-supporting mineral (in tiny amounts) in the human diet. There is no dietary requirement for plastics!



The cover framework can also be constructed from 2-by-2 inch mitered cedar. The glazing we have most often used is Kalwall brand, 40 mil, fiberglass reinforced polyester. It holds up better than glass in hail storms and weighs much less. My neighbor built a dryer but used acrylic glazing. The acrylic was much cheaper initially but needed replacement after three years of use due to extreme yellowing and the formation of numerous cracks. New dryers made by friends and neighbors use locally available clear, corrugated fiberglass greenhouse glazing. It is much less expensive than Kalwall while appearing to be just as durable. Our favorite glazing, and the one we currently use, is corrugated polycarbonate. It is the most durable, yellows the least over time, and remains the least brittle with constant exposure to sunlight. The end channels can either be sealed, using chunks of properly shaped wood and silicone caulk, (the foam strips sold for the purpose break down in heat and sunlight), or they can be left open. The dryer works well in either case, although sealing the ends may keep the black collector sheet somewhat warmer and cleaner.



We have received a number of technical questions about the physics of the glazing, in terms of both necessity and function. As light passes through the glazing and hits the black collector sheet most of it heats the collector. The collector radiates this infrared energy both downward toward the food and upward toward the sky, heating the airspace between the collector and the glazing. The glazing keeps any wind or rain from pulling this heat off the black collector sheet by convection (wind) or conduction (rain), insulating the airspace and further warming the dryer. Adding a second layer of glazing would further insulate the airspace in really cold weather, but you would risk reaching a point of diminishing returns, since added glazing means more incoming light lost due to reflection from, and absorption in, the extra layer of glazing.



And if you think you can simply dry foods in open sunlight or with a mere plastic/glass covering, guess again! Some solar dryer designs actually depend on sunlight hitting the food to generate heat (the Fodor design in Mother Earth News publications). This link will take you to some research showing the nutrient loss using this option, both with direct sunlight and with clear covers. Plastic/glass cuts out UV-B radiation but not UV-A, so a layer of black metal or cloth is a necessity to keep nutrient levels as high as possible.









Glazing Material Characteristics Kalwall, Filon, Lascolite, etc. FRP, fiberglass-reinforced polyester Durable, light, impact-resistant (although 2-inch+ hail causes cracking), good light transmission, surface degrades over time and yellows slightly, rough surface of old glazing requires occasional scrubbing with bleach/hydrogen peroxide to keep it clear, easily cut



Glass Glass Fragile, heavy, variable impact resistance, great light transmission, no surface degradation or yellowing over time, cheap if recycled, hard to cut to size, harder to mount on a frame



Lexan, etc. Polycarbonate Very durable, light, highly impact resistant, great light transmission, no visible yellowing or surface degradation, expensive, easily cut to size, will eventually get more brittle, like all plastics



Plexiglass, etc. Acrylic Somewhat fragile, light, poor impact resistance, good initial light transmission, cracks and yellows with exposure to sun and heat, fairly inexpensive, hard to cut without cracking



Thin films Polyethylene, etc. Fragile, very light, fairly impact resistant, great light transmission, degrades quickly in sunlight unless cross-linked polymer, UV-resistant material is used, cheap if recycled from commercial greenhouses but can be pricey otherwise, very easily cut to size Glazings, in Summary

Instead of the black cloth used in the original experiments we now use a layer of thin aluminum sheet, painted with "Barbeque Black" paint on both sides, stapled to the underside of the cover framework. The top is black to absorb the sun's heat and the bottom is black to re-radiate that heat onto the food. You could use steel sheets (28 gauge or lighter - not galvanized so paint will adhere better) or used "printer plates", but aluminum "flashing" is easy to find in 2-foot widths. The black metal heat collector is more convenient to use, less messy, and probably less expensive in the long run than black cloth.



One way to improve the collector's efficiency is to use a "selective surface" or "Black Chrome" paint on the top layer of the metal sheet. These paints absorb sunlight just like common black paint but have less emissivity at lower wavelengths. This means that they re-radiate less heat back upward into space once they get the metal hot. At a typical temperature of 150F on the metal this could mean a 35% efficiency increase. But it comes at a much higher cost and you can only use it on the top side. If you use it on both sides it will reduce the amount of heat radiating toward the food. And if you are at a high altitude or low latitude the added efficiency will lead to higher temperatures which are more likely to burn your food.



The cover framework is attached to the dryer base with T-strap hinges on both the north and south sides. These were made into loose-pin hinges so you can open the dryer from either side by pulling the pins and lifting the lid on the opposing side. A bent steel rod can be inserted into the hinges to prop the lid open. Right angle brackets are fastened to the south edge of the roofing below each screen (where there is a hinge placed) to keep the trays of food from sliding off the downhill side.



All of the cedar is coated with a homemade sealant: melt 1 pound of paraffin wax, remove from heat and vigorously stir in 3 quarts of linseed oil and 1 cup of gum spirits turpentine. When cool it looks like crystallized honey. Apply liberally with a brush. This is also great stuff for windowsills or exterior trim where you want water repellency. Recoat in subsequent years when needed. The legs and under-framework need no other sealants if you use the treated wood option. ACQ treated lumber is the newest option and supposedly more environmentally safe.





Improvements and Alternatives

a shelf or table nearby as a handy work space

removable or folding legs to facilitate winter storage if you want to put it away



1-inch square aluminum framework for the collector instead of wood



a reflective white/silver wall on the back side of the dryer to increase solar gain at higher latitudes



use an open-weave shading cloth or window screen over the collector to reduce solar input in hot-sun areas (such as nearer the equator or at higher altitudes) giving you the option of removing it on cloudy or partly cloudy days to maximize solar gain



east and west sides enclosed or shielded to prevent excessive cooling by cross-flowing winds under the food screens



the collector can also serve as a cold-frame cover if the black, heat generating material is removable or separate



other screen materials (such as bamboo) could be substituted as long as they are safe for direct food contact



The above is mainly excerpted from "Feeding Ourselves" (shown below), by Larisa Walk, available as either a download or as a physical copy.





Keep in mind that YOU CAN DO THIS.



You can substitute what you have for what we've used.



You can use recycled materials.



You can use what's most readily available for building materials in your area.



You can even use your parked car as a food dryer. Just set up screens, cover with black cloth, park with the biggest windows facing the Equator, place the screens in vehicle so air can circulate around and under them, and leave a window open a bit to let the moisture out. This is a much better use for a car than driving it, so why not make it multitask?



Long-term storage



In response to a number of questions about dried food storage, we store all of our dried and canned food in glass canning jars, in a cool, dark room (our pantry). Plastics are not a reliable barrier against moisture and dried vegetables must be kept completely dry (fruits aren't as picky - they can be somewhat pliable and still store well). We actually use old blue-green quarts and half-gallon jars, along with the old-style rubber rings and zinc-coated covers. Both light and heat damage nutrients, so keep them stored away until you're ready to use to maintain food quality.







Our Book



If you are looking for more detail than can be gathered on our site, check this out:





Our latest co-authored book, "Feeding Ourselves", now in its second edition, includes our unique solar food dryer and other energy-saving food preservation methods ( steam-juicing and steam-canning) that fit into our overall scheme of nourishing ourselves year-round in a fairly harsh climate. This edition has been updated with our years of experiences in raising and utilizing staple crops like gluten-free grains, legumes, and nuts.







To see an Adobe PDF file of the second edition's entire covers and table of contents, just

From the back cover of Feeding Ourselves: This book came about after many decades of trial and error in the quest for real, homegrown, organic local cuisine throughout the entire year. We've been gardening and preserving food to fuel our off-grid homestead lifestyle since the 1970's, determined to sever our reliance on the petrol-fueled American food system. Some of our explorations led to us to rediscover and integrate old methods, like root-cellaring, into our routines. Other experiments resulted in the design of our solar food dryer. Our approach to this effort is from a vegan, gluten-free perspective. Over the years, Larisa taught workshops on food preservation, including many summers at the Midwest Renewable Energy Fair. In 1997, she decided to write a small book, "A Pantry Full of Sunshine", which she self-published to answer the frequently asked questions that couldn't be covered in an hour-long workshop. Now, over a decade later, this little book's limited scope became evident and we felt that there was much more to reveal about how we put food on our table. This seasonal guide features down-home advice from Minnesota. There is a focus on energy efficiency, both in cooking and food preservation. Whether you want to grow and eat vegetables, fruits, legumes, grains, nuts, seeds, herbs, spices, or sweeteners, we hope our approach will inspire you to explore feeding yourself, from the ground up. We intend this book to be merely a source of ideas and food for thought. While this is what works for us, it may not suit you, and is not meant to be a detailed plan of action. Feel free to creatively adapt our ways to fit your circumstances. Enjoy the abundance!To see an Adobe PDF file of the second edition's entire covers and table of contents, just Click Here

Physical copies of "Feeding Ourselves" (184 pages, spiral-bound) cost $23.50 each, postpaid in the U.S. (please add $1.38 sales tax if you are ordering in Minnesota), or $20.00 plus shipping elsewhere in the world. Contact us for international shipping costs. All others can simply send a personal check, traveler's check, or postal money order to: GeoPathfinder/Larisa Walk/Bob Dahse

30319 Wiscoy Ridge Road

Winona, MN, 55987-5651

OR: To order a physical copy of "Feeding Ourselves" using PayPal, Click Here . Clicking this takes you (very slowly if you have a dial-up connection) to a new screen with a "Buy Now" button, and this links to PayPal's secure order form where you can pay by credit card, checking account, or an existing PayPal account balance. OR: To order a downloadable Adobe PDF file of "Feeding Ourselves" for about half price ($10.00), just Click Here (requires a free Adobe Reader download to read the PDF file). Clicking the book download link takes you to PayPal's secure order form and gives you a link to the PDF via Payhip.com. The file size is over 8 MB so, depending on your connection speed, it may take some time to download.











Yes, we have stainless steel screens for sale



Hopefully, you may be inspired to try building your own solar food dryer, maybe even one like the model we designed, shown further below. If you need some stainless steel dryer screen, in previous years we've ordered it for dryer workshops organized in our area, where a group of 10 folks got together to bui ld their own solar dryers. We now keep woven stainless screen material in stock, shown above. You c an order pre-cut screens directly from us. We have handled anywhere from .018" to .023" wire sizes and they all work well, but .018" is a more "open" weave (61.5%), is cheaper to ship, and will not sag in the middle of a 2-foot screen full of food. We have type 304 stainless steel, plain weave, 12-mesh, .018" wire size, dryer screening available for immediate shipment. It comes to us on a 4-foot wide roll and we cut it into 2-foot by 2-foot pieces designed for our radiant dryer, normally shipping it rolled into a 6-by-6-inch box. For really large orders we sometimes send it in a flat, 2-by-2-foot box. Please do not ask us to cut into sizes perfect for some other dryer design since the pieces rarely cut perfectly from our 4-foot rolls without significant waste of an expensive and energy intensive resource.



For really quick ordering within the continental United States , just use one of these E-Bay links:

For 2 screens shipped via USPS Priority Mail

For 4 screens shipped via USPS Priority Mail For 6 screens shipped via USPS Priority Mail

For 8 screens shipped via USPS Priority Mail

Or we will give you the cheapest possible quote to your address:



We can sell screens for $3.00/ square foot, or $12.00 per 2-by-2 foot dryer screen, plus actual shipping costs to your locale. To get a shipping quote ,

simply send or e-mail us



the number of screens you would like. There is a minimum order of 2 screens, and because it comes off a 4-foot roll we only sell it in multiples of 2 screens (either 2, 4, 6, etc.). For instance, to build a 4-by-4-foot dryer (the minimum we recommend) you will need 4 screens, totaling $48.00 plus shipping.



Once you have received your shipping quote,

If you wish to proceed with an order using PayPal (which accepts all major credit cards, checking accounts, and e-checks), we can either send you a PayPal invoice or you can pay the total with shipping either to our account on GMail.com, listed as "bobdowser". Or, if you dislike paying online and are not in a big hurry, just send a check to: Bob Dahse/Larisa Walk

30319 Wiscoy Ridge Road

Winona, MN 55987



We ship via USPS using either the slower, cheaper Standard Post or the faster, more expensive Priority Mail. Standard Post orders ship on Fridays, when we take a weekly trip to town. Priority Mail orders can ship on any regular business day since USPS picks these up from our home.



When you receive your screens we recommend washing them in warm, soapy water. Factories ship them covered with a light coating of petroleum-based lubricating oil that is used in the weaving process. It is best to get that off before mounting them in a frame and using them with food.



If you need the screens trimmed slightly to recess the screen edges back from the edges of a 2-by-2-foot frame, we recommend using a metal shears. We use a Stanley model with slightly serrated, chrome-molybdenum steel blades that work quite well. The screen edges are sharp so wear gloves! If you would prefer the screens slightly smaller but you would like us to cut them for you, please mention this in your request.



And if someone reading this gets inspired to order enough materials to organize a dryer building workshop in their own area we'd be happy to post a link here to your website/e-mail address so that others could obtain your leftover screen. For the best price on stainless screens in larger quantities or other widths, you will need to order it in 100-foot rolls. We had been getting it from Cambridge International (formerly Cambridge Wire Cloth, in Massachusetts). To get their most recent price quote, you'll have to e-mail them. With a 24-screen minimum order this is not the best option for those wanting pre-cut screens.



We currently order 100-foot rolls from a company in Pennsylvania called Darby Wire Mesh. Again, their price on large rolls is good but individual pre-cut screens cost a lot. Another company, in California for those closer to the West coast, is TWP, Inc. Their site, like Darby's, is user-friendly, with direct links to buy the screening. And an e-mail correspondent found another site, City Wire Cloth, with a minimum order of $100. They offer a 4 x 10-foot piece of type 304, .018", 12 mesh.



Either way, don't expect low prices! This is a life tool, eminently recyclable, and will no doubt be usable for 7 generations. If you can find a local metal-working shop that has leftover stainless screen from some industrial contract job, or if you can find some in your local metal "scrapyard", the recycling price will be probably be much lower.







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Some Photos



These are sliced red sweet peppers ready for a day of sunshine. They can also be cut using a potato "frencher", which makes 1/2-inch by 1/2-inch pieces instead of strips.



These are "drying" tomatoes. The variety is "Principe Borghese" though any small, meaty tomato works well. We cut them in half and squeeze out the juicy seed cavity (you can drink the "innards"), then place them "skin side" down on a stainless steel cookie sheet until somewhat dry, then move them to the stainless screen.



Ah, the middle of Summer and we're up to our eyeballs in sweet corn! Even growing an open-pollinated variety that doesn't mature equally, we still have a hard time eating more than a dozen ears per day when they really start maturing quickly. Here we see about 150 ears, picked the night before and steam-blanched, cooled overnight on the kitchen counter, and cut off the cobs the next morning. The overnight cooling actually starts the drying process. And if we tried to do the whole process in the morning, we wouldn't have it out into the dryer until noon. That would be a terrible waste of sunshine!



This is a close-up of two trays of sweet corn. The top one is freshly loaded in, sitting at the top of the dryer so it gets the maximum warmth on its first day. The bottom tray has been drying for one day and is almost done. This variety called True Gold, but any open pollinated standard variety works nicely. We use it in soups, stews, and just rehydrated with water. As with all processed foods, it's not as nutritious or delectable as fresh corn, less fresh-like than frozen corn, but tastes rather like canned corn. And no additional energy required to preserve or store it. Depending on how hot and sunny the weather is, the sugars in the corn can sometimes end up more or less "carmelized", making the flavor more intense, like a roasted ear of corn.



This shows part of the solar dryer filled with apple chunks, from wild apple trees growing near our home. They've been cut in half, cored, and run through the "French-fry" cone on the food chopping attachment of a "Kitchen-Aid" Mixer. Note that we have left more airspace between pieces on the lower screens since the dryer will not be as hot there. The upper trays can be more densely laden.



This is a close-up of the apple pieces on the stainless steel screen, ready to dry. In late September, with our lowering sun angle and very cool nights, they take 2 or 3 sunny days to fully dry.



Now it is mid-October and we have found a bunch of delicious Agaricus Campestris ("Pink-bottom" Agaric) mushrooms growing in and old pasture and orchard. Talk about perishable! They may last a couple of days if you keep them cool enough, but how many can you eat at once? We were finding a couple of pounds per day for nearly two weeks and here is a batch going onto stainless steel cookie sheets. They are cut into 1/4" slices and carefully laid out to allow air flow. Mushrooms are the exception to keeping sunlight off foods to preserve nutrients. Mushroom gills exposed to sunlight actually increase the Vitamin D content significantly, to medicinal or supplement levels (this can happen when freshly cut or after drying). So we usually first set the cookie sheets of cut up mushrooms out in the sun (with a screen over them to keep flies off). The next day they go into the dryer to finish. We sometimes alter this schedule to fit with weather constraints.



Here you can see a typical mid-October dryer load, shot from the South. At the top, in the warmest spot, is a tray of freshly cut mushrooms. Below them is a batch that has dried for a day on cookie sheets and is transferred to cotton kitchen towels to allow better air flow, to catch small pieces that might go through the dryer's stainless screens, and to free up cookie sheets for the next fresh batch. We start them on cookie sheets because the spores given off before they begin drying can stain the cloth. Below them are white oak acorns, drying in the coolest spot to ready them for shelling and processing.



What can we do with all of these highly perishable berries! This is a typical daily harvest of raspberries from our patch. The variety is Autumn Bliss. This is what's left after we've eaten what we can handle fresh! What to do with the rest when you're maxed out on "raspberry this" and "raspberry that"?



Well, as with many fruits, you can put them on a stainless steel cookie sheet and smash them with a potato masher to prepare them for the food dryer, or you can use another piece of kitchen equipment to turn them into bottled juice and use the remains on a cookie sheet for the dryer. We put two day's harvest into our stainless steel steam juicer (after holding the first day's picking in a cool spot). This will remove the Pasteurized juice for bottling, leaving the pulp and seeds behind. The pulp-seed mix can be solar dried (on cookie sheets as a "fruit leather") or canned in the steam canner, depending on the weather. Blackberries really need their seeds removed from the pulp before canning or drying as they are larger, more numerous, and more "gritty". There are various appliances available for doing so, most of them simple hand-cranked devices. More on these alternative methods can be found on our Energy-Wise Canning & Cooking page.







And this photo is from a contact in Tennessee who built their dryer on a platform that can be easily attached to or removed from a wheeled cart.



