Finding an appropriate thermometer was a challenge. The temperatures required for drying are in the range of 48ºC to 66ºC, or even lower for herbs, so we could not use a normal oven thermometer (they usually start at around 150ºC). We ended up buying a $10 barbecue meat thermometer that measured the appropriate low temperature range. The dial face only shows incremental temperatures in bands of colour for particular cuts of meat; the lowest temperature shown was 54ºC. We calibrated the thermometer using a temperature probe and marked the temperatures on the dial face in 5ºC intervals from 30ºC to 50ºC so that we have a more accurate feel for what is happening temperature-wise inside the cabinet.

The hinged back vent is used to maintain the correct internal cabinet temperature during the drying process and needed a stay to hold the door in varying positions from fully closed to fully open. The adjustable stay is homemade.

Anticipating the need to make drying screens, we had picked up two aluminium flywire screens from the tip, which we were going to cut down to the correct size to fit the cabinet and finish with new mesh screen material. There was much discussion in Fodor’s book on the best material to use as the mesh on the drying trays. His final recommendation was to use polypropylene screen material, which, unfortunately, we could not source locally. We could only find this product on-line from US websites. The other alternatives were fibreglass mesh, which may not be safe for food contact, aluminium mesh, which can react with acidic foods such as tomatoes, and stainless steel mesh, which is expensive and also difficult to source in food grade quality. Stainless mesh is also hard to bend and work with.

Eventually we purchased four Wiltshire non-stick cooling racks measuring 510 mm by 365 mm from our local supermarket. These racks are not ideal as the holes in the drying are at 12 mm spacing — obviously not as fine as other screening material, but the best local option we could easily find. We joined the four cooling racks with pieces of dowel, which made two drying trays that could slide neatly into the cabinet. Unfortunately these trays are also about 100 mm short front to back inside the cabinet, robbing us of some drying space.

We sat the completed solar dryer in the sun for a couple of days to vent any remaining fumes from the construction process before we used it for the first time.

Our first batch of produce consisted of apricots and zucchinis, which took two days to dry. We sliced the zucchinis about 3 mm thick and removed the stones from the apricots and cut them into quarters. Both days were sunny, around 34ºC, and the dryer was in operation from 9 am to 7.30 pm. We set up the dryer facing north, but as the days wore on we did re-orientate it more westerly to get the sunshine for the longest amount of time.

When we read Fodor’s book, we were a little concerned that, as it was written for North America, the dryer may not cope with Australian summer heat. Would we be able to keep the temperatures in the correct range? We were pleased to see on these hot days that with the back vent fully open the temperature stayed nicely in the 55º to 60ºC range. We turned the produce over mid-way through the first day and swapped the trays top to bottom inside the dryer. Overnight we closed the vent and took the dryer indoors.

Since then we have done subsequent batches of assorted excess fruit and vegetables including eggplant, plums, apples and more zucchini. We have used the dryer on a cooler 24ºC day and, with the vent closed, the cabinet temperature stayed well within the 55°C to 60ºC drying range. We have had one batch interrupted by bad weather after just one day of drying.

We closed the vent and brought the cabinet inside for two days before we could complete the drying on the fourth day — probably our worst-case scenario for not having fitted the electric drying backup! We thought that the whole batch was likely to be ruined but in fact there were only two pieces of food that had become mouldy and had to be thrown out. We have been excited to taste the finished dried product as the drying seems to really bring out the flavour. Thus far everything is storing well in jars.

Fodor’s book concentrates very much on the ‘how to’ of making the solar dryer, and only briefly covers other important details, such as how to prepare and how long to dry different foods. It only provides a handful of recipe ideas for using the dried produce. We really wanted some more information, and luckily stumbled across an Australian book on the Friends of the Earth website called Drying Food by Ricky M Gribling.

Although this book is written for use with commercial food dryers, it has been very useful, as it has filled in some of these knowledge gaps. It covers drying a wide range of different foods, and has information on preparation and drying temperatures and times suitable for the solar dryer. It also has many recipes with hints on how to best use the dried product in cooking. We can see the potential for lots of experimenting in the future and we realise that we still have a lot to learn.

The solar dryer looks great and appears to work very effectively, but it does need two people to move it around, especially to get it through doorways. It is a bit heavy and awkward on your own, although we accept that some of that is our fault through choice of building materials.

We have also observed that our drying trays have limitations because as items dry they shrink in size and can fall through the holes in the racks. This is something we will probably have to re-visit as time goes on: we need an alternative. Otherwise, we are really happy with the outcome of our latest holiday project and look forward to the ongoing benefits of healthy, high quality food preservation that the solar dryer will bring.

 

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