Energy Efficient Food Preservation
Once you've gotten started with gardening, you'll soon have to find a way to deal with the surplus (hopefully you've planned for this!). Not everything can be eaten fresh. Some foods may need to be stored for later consumption. 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). Growing and preserving food is a time-honored way of maintaining a "just-in-case" food inventory instead of relying on getting to the store "just-in-time".
- If your interests lie more in first producing more of your own food (despite an uncooperative climate) instead of preserving it, have a look at our Eating Year-Round from the Garden page.
- If you'd like to know why you might want to grow your own food, how to supply the nutrition you need from those foods, how to deal with foods that do not require drying, canning, or juicing, or how we have turned our nearly 30-year vegan diets into a practical and sustainable lifestyle, try the Vegetarian Homesteading page.
- We don't do anything in a vacuum. It's all part of an integrated,
synergistic whole. Learn more about what we do, who we are, and what else we can offer on our Home Page.
- And, if you would like to read more about what Larisa and Bob are currently up to on their homestead, just Click Here to reach our blog.
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 build their own solar
We now keep woven stainless
screen material in stock, shown at the left. You can 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, is cheaper to ship, and won't 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.
comes to us
on a 4-foot wide roll and we pre-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. You can also find more details about ordering it below the following section about our food dryer design.
Of course, food that is fresh is best, but our Minnesota winters challenge that approach.
The next best thing to harvesting just before your meal is to have food that is "live stored" - food that keeps itself. All you have to do is provide the right microclimate for the veggies and fruits that have this hibernation factor built into their biological cycle. We recommend reading "Root Cellaring" by Nancy Bubel for inspiration on building and using a root cellar. Our own methods rely heavily on insulated picnic coolers (owned by most folks but unused in the winter months) which are stored on the north side of the house, then moved to our sauna (not in use in the early fall), and eventually to an insulated in-ground tank in our garden shed or our pantry's below-floor "pit" when really severe winter weather threatens. The handout from the Midwest Renewable Energy Fair shows temperature and humidity conditions for a variety of vegetables/fruits. "Root cellaring" is for more than roots! For a free Adobe PDF file download of this hand-out, just Click here.
Next in our nutrient-saving, energy-saving hierarchy is food drying, or dehydration. Solar-dried foods don't require fossil-fueled energy inputs to preserve them or store them, unlike refrigerators and freezers. Just a tightly sealed glass jar will do! No electricity required, just sunlight from a safe nuclear power source about 93 million miles away.
There's much more about our Solar Food Dryer farther down on this page. But if you're looking for more detail than can be gathered on our site, check out our book:
Lots of folks have either downloaded or purchased a hard copy of "Pantry Full of
Sunshine", Larisa's book based on many of the questions she fielded at workshops
about her unique solar food dryer and her other energy-saving food preservation
methods, like steam-juicing and steam-canning.
Our latest co-authored book, "Feeding Ourselves",
includes all of "Pantry's" information plus it is greatly expanded to show how
food preservation fits into our overall scheme of nourishing ourselves
year-round in a fairly harsh climate. And it is updated with recipes that better
reflect our most recent dietary changes, including entirely gluten-free grains,
with information on growing and processing home-grown foods of all sorts. If you
liked "Pantry" you will love this one! To read a complete description go to our Products & Services page.
To see an Adobe PDF file of the 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), Click Here or the button at the left (requires Adobe Reader
to read the download). Clicking this takes you to PayPal's secure order
form and gives you a link to the PDF via Payloadz.com. The file size is
7.53 MB so, depending on your connection speed, it may take some time
A Solar Food Dryer That 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 2x2 foot stainless steel screens framed in 2x2 inch cedar, and one of the 4 by 4 foot heat-generating solar collector panels raised for access. Sunlight shines through the clear glazing, lowering the frequency of the light to make more infrared (heating via the greenhouse effect). Moving inward, it then hits a black-painted aluminum sheet, heating the metal. The back side of the black aluminum re-radiates heat onto the food below, causing the food to heat up and lose moisture while keeping 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!"
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, 2x2" 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!
Here 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's 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 (and most costly). But other types of glazing are available that may be recycled or cost less and work better for you. You will find more to read about these below. The black metal sheet could be steel, aluminum, or whatever is at hand, including black polyester or polypropylene cloth.
The food trays could be 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 but this may prove too expensive for your needs. Still, 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.
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 it is far slower when drying anything but thin greens. 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 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. Think about forced-air heating versus a wood-stove in a home. The wood-stove radiates heat directly onto your clothing and 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 evaporate, creating a 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 it through the food actually causes some cooling 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's all in the path of radiant heating, and this combines to speed moisture loss, even on less than optimal drying days.
Another 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) do 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:
And 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
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 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 from www.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 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 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 silicone caulk or the foam strips sold for the purpose, or they can be left open. The dryer works well in either case, although sealing the ends may keep the black collector sheet somewhat cleaner.
We have received a number of technical questions about the physics of the glazing, in terms of both necessity and function. When sunlight passes through a light-transparent material it changes a bit. Most texts speak of light "slowing down" when passing through air, water , clear glazing, etc. In reality light does not slow down even though it appears to. Light always travels at "light speed", relative to an observer, but when it passes through a transparent medium other than a complete vacuum its frequency shifts downward (the "red shift"). Supposedly the light regains its frequency on the other side of the glazing, but no energy conversion is 100% efficient, and some of the downward shift still remains. This makes more visible light out of ultraviolet (UV) light and more infrared (heat) out of visible light. So the glazing not only keeps the wind from pulling heat off the black absorber sheet by convection (wind), it also actually helps create more heat for the absorber to radiate downward onto the food.
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/cloth is a necessity to keep nutrient levels as high as possible.
Glazings in Summary:
|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|
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 repellancy. 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
- removeable or folding legs to facilitate winter storage
- 1-inch square aluminum framework for the collector instead of wood
- adjustable slope to accommodate seasonal sun angle changes or for high latitudes
- a reflective white/silver wall on the back side of the dryer to increase solar gain at higher latitudes
- brown, green, red, or blue paint on the collector's metal sheet to avoid over-heating foods when the dryer is used nearer the equator or at higher altitudes
- or use an open-weave shading cloth or window screen over the collector to reduce solar input in hot-sun areas, giving you the option of removing it on cloudy or partly cloudy days to bring the temperatures back up
- 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 coldframe cover if the black, heat generating material is removable or separate
- other cheaper screen materials could be substituted as long as they are safe for direct food contact
The above is mainly excerpted from either "A Pantry Full of Sunshine" or from "Feeding Ourselves", by Larisa Walk, both 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, put the screens in the sun's path, and leave a window open a bit to let the moisture out. This is a much better use for a car than driving it, but why not do both since you're already doing one?
And 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-gallons found at rummage sales, along with the old-style rubber rings and zinc-coated covers. This helps to keep the light out even when the jars are out of the pantry. Both light and heat work against the nutrient value of the contents, so any way that you can reduce them improves storage time.
Stainless Steel Dryer Screens:
We sell screens for $3.00/ square
foot, or $12.00 per 2-by-2 foot dryer screen, plus actual
shipping costs to your locale. Click on the button at left to get a shipping quote by sending us your zip code and the number of screens you would like, or by E-Mailing Us Here (or if this link doesn't work for you, simply use our Secure GMail.com account listed as "bobdowser"). 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.). To build a 4-by-4-foot dryer you will need
4 screens at $48.00 plus shipping.
- Buying Screens from GeoPathfinder: Once you've received your shipping quote, if you wish to proceed with an order using
PayPal (which accepts all major credit cards), we can either send you a PayPal invoice or you can pay the total
with shipping either to our e-mail address at yahoo.com, listed as "geopathfinder", or our other account on GMail.com, listed as "bobdowser", using PayPal.com.
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 normal 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's 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 (firstname.lastname@example.org). 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
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.
Support Our Research: Have you found the information above helpful? The design for the dryer is patent-free so we make no income from it. But if you would like to make a financial contribution to our on-going research in these or any of our other efforts, just Click Here to get a PayPal payment link that allows you to send us any amount you wish.
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" which is available commercially or through Seed Saver's Exchange. 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. The variety we're growing is called Tru Gold, and it's available commercially as Organic seed. We use it in soups, stews, and just rehydrated with water. As with all processed foods, it's not as nutritious as fresh corn, and not as fresh-tasting as frozen corn, but Summer doesn't last long up here, and frozen corn uses more energy to keep it cold than it could ever provide to your body! Depending on how hot and sunny the weather is, the sugars in the corn could end up more or less "carmelized", making the flavor actually sweeter and more intense.
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.
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's mid-October and you've found a bunch of delicious Agaricus Campestris ("Pink-bottom" Agaric) mushrooms growing in your sheep 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? I was 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. So we 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.
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. The nut "meats" will be boiled to remove some bitter tannins, then laid out at the top of the dryer. When dry they can be ground into nut flour or chopped up for use in pancakes, breads, etc. But white oaks only produce seeds every 6 - 10 years, so be prepared!
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"?
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.
This is the fully (and obviously well used) assembled steam juicer. The bottom pan holds about an inch or so of water (instead of gallons of water!) that boils to make steam. The steam rises through the next layer, which is where the juice collects. The third layer, most of which is nested in the second, is the perforated basket of berries. The top layer is, surprise!, just a top. The silicone hose hanging down the front has a clamp on it to retain the juice until you're ready to tap it off. And to reduce distillation of water into the juice pan (from the cold stainless top), especially before the berries get hot enough to release juice, we normally run it with a folded towel on top for insulation.
Our biggest use of the steam juicer probably occurs when we do tomato processing. We quarter our canning tomatoes and extract a lot of the juice, bottling it for soups and fresh drinking. We then pack the remaining pulp into quart jars and steam-can them. No boiling is required to get a thick sauce, and the small quantity of water used (compared to boiling water bath canning) really saves a lot of time and energy!
And this is the result. Seven, 16-ounce, recycled "Grolsch" beer bottles hold the product of the process (actually there was one more that I removed from the juicer and heated to boiling separately after the juicer had cooled and the pulp dripped totally "dry"). The bottles get filled to the top with hot juice, straight out of the hose, the top is clamped on with the wire bails, and you're done! Well, actually just a little bit of rinsing to do on the outside of the bottles from the overflowed juice. We fill about 200 of these bottles each year, primarily with apple juice. We don't use the steam juicer for apples because of the volume we do. Before we sold the equipment to someone doing an even higher volume of apples we hammer-milled the apples into a pulp and pressed the pulp in a hydraulic press we designed (built by a local metal shop). Now we simply run the apples through a medium-sized cone-shredder on our Kitchen-Aid mixer. Then we strain the juice, heat it to boiling, and pour it directly into the bottles. No further processing necessary!
Here you can see the process of preparing some small pears for juicing. The raw product is in the wire egg basket at the top. The knife and edge-sharpened spoon used to cut the pears in half and scoop out the cores are at the bottom left. The pulled-out stems are above them and the the pear halves. The cores that are about to become treats for our sheep are at the left. And the cut-up pieces of pear are in the steam juicer. A steam juicer full of cut pears made over 7 pints of very sweet juice and 4 cookie-sheet trays of fairly dry pear pulp for the solar food dryer. You wouldn't think that this pulp would have much flavor, but even with lots of juice removed the heating that it undergoes during drying tends to sweeten it (semi-carmelization) and concentrate the flavor. Just try to avoid eating a second piece!
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. The traveling food dryer has arrived!