Preserving food, part 1. the solar dehydrator
Those of you who have read this blog regularly know that I am very concerned about a probable food crisis and about food security (see my previous posts about population and agriculture, and about GM food and the upcoming food crisis).
Being a practical man, I look for practical solutions and in this case, this means working toward self sufficiency in food. This is one of the reasons why we produce most of our vegetables and are looking into grain production (see the post about Growing grain).
One key area of food self sufficiency is the ability to store food for longer periods of time, so summer surpluses are available in the winter, when the gardens and orchards do not produce much.
Over the past year, we have tried various methods of preserving food. Freezing is the easiest option, but it is not entirely satisfactory because to store any serious amount of food this way requires an initial investment and a lot of energy, but mostly because power cuts (which are likely to become more frequent) make it unreliable. Canning and bottling (which we will look at in further posts) are better options and we have successfully bottled some of our tomatoes and courgette surpluses this year, and have made vast amount of apple chutney and pasteurised apple juice last year, but the process requires large amount of energy, as the food has to be pasteurised, and in most cases, cooked, before storage.
You will also know from our previous post that we have also tried successfully lactic fermentation of vegetable, a traditional method of preserving food (think of sauerkraut, but also of Kim chi, the Korean national dish). Lactic fermentation gives excellent results and we will certainly keep using it, but today’s post is about our latest experiment in food preservation, the solar dehydrator.
We have been drying herbs from the garden for a few years, but hadn’t really found a satisfactory way to do this, in the sense that we had to use a dehumidifier for days in the attic before the herbs were dry enough for long term storage. So this year I decided to try something different. For 106 euros, I got an electric dehydrator, which works fine but still uses at least 250 w of electricity.
The idea of a solar dehydrator came up almost by accident. I had seen a very large solar dehydrator used for commercial dried herb production in a farm in the South of France, but hadn’t really thought of doing a scaled down version until I looked on the Internet and found out that it had already been done.
As we had a woofer with good carpentry skills here at the time, it ended up being one of his project. It took him a day to build the box, and another day to build the solar heater. This is what the result looks like:
On top is a drying box with drawers make of Insect screen (stretched on a wooden frame). The drying box has a large rectangular hole at the bottom in which the top of the solar heater fits neatly, held in place with 6 bolts. On top of the box is another hole for the solar powered fan (you can see the little solar panel on top of the roof of the box).
The solar heater is a wooden box containing a sheet of corrugated iron, painted black, with a sheet of clear plastic to cover it.
The air circulates through the solar heater, which has a series of large round holes at the bottom (not clearly visible on the photograph), and comes out at the top into the drying box (through another series of large round holes), pretty hot. The small solar powered fan on top of the box sucks the hot air from the solar heater through the drying box.
We used:
2 sheets of 1/2 exterior ply (for the box, and also for the bottom of the solar heater)
2 lengths of 7×1 larch (for the solar heater) you could also use red deal / pine or even just treated timber)
1 sheet of clear plastic (recycled from an old roof)
1 sheet of corrugated (roofing) iron, 3 m long. Cut what you need for the roof of the box and use the rest for the solar heater
1/2 tube of silicone mastic (to make the solar heater airtight)
1 length 2×2 (framing for the box)
1 length of 2×1 (for the drawers inside the box)
3 meter of Insect screen, 600 mm wide (for the inside drawers)
1 small solar powered fan (a Google search will get you one for less that 50 euros, although if I was to do it again, I’d probably spend a bit more and get a slightly more powerful one)
1 roll of draught proofing strip (to make the door airtight)
Total cost around 100 euros, same as the electric dryier, but surely more eco-friendly!
Ciara didn’t believe that the thing would work, but after we dried a kilo of fresh mint in less than two (sunny) days in September, she had to admit that this is a lot more efficient than a dehumidifier in the attic. Later on, we also used it to dry chilli peppers, as, thanks to Frank and Christina diligence, we have a bumper crop of those this year.
The monster is now put away in a shed for the winter, but Theo is looking forward to selling loads of dried herbs in his farm shop next summer 
Christophe