Off-Grid Tealight Slow Cooker

Intro: Off-Grid Tealight Slow Cooker

This idea is about as simple as they come, and a few people
will doubtless read this and think “duh… bit obvious”, but the idea for this came from a conversation about whether it was possible to power a slow cooker from an off grid 12V setup (the answer to that being “yes, but it needs a lot of batteries”). Which got me thinking of alternative off-grid ways of slow cooking, which in turn led me to the question “what would provide a low level of heat over a 6-8 hour period?”.

The answer is of course: Tea-lights – those pesky little things that clutter up a draw or cupboard for 99% of the time, until that one occasion you have a power cut. They burn steadily and reliably, and they come in all manner of burn duration times from 3 to 10 hours.

Anyone who’s done any hiking or camping in the UK will have come across the Trangia – it’s a brilliant all-in-one stove & pan setup that runs on meths; when cooking the pans nestle in a sort of container-cum-windbreak, and I thought that type of design would be a good place to start for building something that was solid, capable of handling a large stock-pot (with about 7 litres of capacity), and would provide sufficient shelter for what boils down to a candle-powered cooker.

I know this is by no means the only way of doing it, and I suspect this isn’t the best way of doing this, but the principle is sound and I’ve used it to make a slow cooked meal so I can claim it does genuinely work

So on with the guide….

What you’ll need:

· A stock pot to cook in

· Timber

· Candles

· Screws / nails / wood glue

STEP 1: Size & Plan Your Build

What size stock pot you go for informs your build. My stock
pot had a 24cm diameter, so I settled with a design that would be about 30cm x 30cm and about 8” deep in total. I was also wanting to use materials I had lying about in the shed so decided to use some butchers block workstop offcuts, and a length of 6” wide dressed pine; though what you use is of course your own business.

STEP 2: Build a Box

This can be as simple or as complicated as you want to make it. For me I used butchers block worktop as the top and bottom of the box, and used the 6” timber as the sides, and glues & screwed the whole thing together. From there I cut out a 24.5cm diameter (the diameter of the stockpot plus a little extra) circle in the top of the box, and screwed rubber feet to the bottom for reasons I’ll go into next. The height of the box was specifically set up to ensure that once the tealights were inside the box, the base of the stockpot would be about 2-3cm above the tealight where the flame was hottest (the stockpots handles rested on the top of the box to stop it dropping all the way through – see the pictures if you’re not sure what I mean) . Once the box was built, I sanded down the rough edges and gave it a coat of woodstain to pretty it up a bit

STEP 3: Make It Candle Friendly

Remember the fire triangle from school? To function, a fire needs 3 things: Oxygen, Heat & Fuel; and the same is true of a candle-powered cooker. Setting aside the heat & fuel elements, the key thing we need to ensure this works is a good flow of oxygen, handily provided in every-day air.

To ensure good ventilation I pulled out the drill and put a series of 2cm holes in the underside of the box along 2 sides of the box, because the box would be off the ground due to the rubber feet I’d fitted, this meant air could be pulled into the box from the underside. I also got the holesaw out and put a 38mm hole in the side of the box, in the corner “opposite” the centre of the right angle of holes on the underside. Inside that hole I fitted a 40mm 12v pc ventilation fan, the logic being that once running that fan will draw old stale air out of the box and allow fresh air to be drawn in via the holes on the underside. The fan was then connected to a 12v power source and was good to go (and before anyone asks, I went for 12V as it would be easier to get off grid, also it would be a slow draw of air and less like to cause the candles to go out).

In fact on my first test cooking I had 6 tealights running and there was no need to run the fan, but possibly if you run a lot of candles it may become necessary

STEP 4: How Many Tealights?

This is a little bit of trial and error – a slow cooker will normally cook at anything from 70 to 85 degrees C. so you need to have enough candles to get up to that temperature quickly, and then keep it at that temperature. For that reason I went – for my first slow-cooked meal – with a mixture of 3 hour and 10 hour tealights; all lit at the same time. The logic would be that the use of additional shorter burn tealights would help get the temperature up to 70-80, and then they die out and the remainder keep the stock-pot hot and slowly cooking. However how many you need will depend on what volume of water you’re using, so a little bit of trial and error may be needed (or you can just cheat and boil the water via some other quick method!)

STEP 5: Cooking on Candles

With the box assembled, it’s time to get cooking.

For my first attempt I took the cowards way out and went for a vegetarian meal on the basis that if it didn’t work, and since it would be unattended, it wouldn’t cause me to be running to the toilet all night.

My recipe involved a litre of stock, and a lot of veg, so I peeled & chopped, put the whole lot into the stock pot, and settled on 3 x 3 hour tealights, plus 3 x 10 hour tealights, this just about worked as planned in terms of getting the temperature up quickly, and then maintaining it for 8 hours of cooking (I was at home so did the odd check on it during cooking) – at one point before the smaller tealights died out the temperature got up to just over 90 degrees C. so I can confirm that cooking meat should be fine (though I’ll not be held responsible for any undercooked meat and subsequent brown rain).

The tealights kept the whole thing at temperature until dinner time, and everything was fully cooked and tasted (as far as I was concerned) really nice. Next step will be some pulled pork.

So that’s about it – simple, effective and does the job. You could probably put some sort of cover over the box to help keep the heat in and keep the temperature up – more of a concern if you’re cooking with meat, but hopefully it’s given some food for thought.

Comments

[terranaght]

I invented something verry similar many years ago but it used a coffee can wrapped with paper towles for insulation and then aluminum fooil for fire protection, and the the bottom of the can was cut to fit very snuggly around 2 quart revereware pan, I used the aluminum bottom sauce pan or you can glue a large coin or washer to the bottom for a heat diffuser,( or it will burn).

you put the coffee can with the open side down on a rack or a few tuna cans to alow for air, and a single tea light in the center the pan fits snuggly above in the cut out in the previous bottom of the can.

you can cook pea soup, rice, lentils and barley with a single tea light, hard red beans take much more time. A towel or hot pad over the lid helps too.
my version works so well because the hot air is trapped by the insulated can until it cools enough to drop out the bottom.
good luck.

[WarmUp]

naked flames inside a wooden container? why didnt i think of that? lol

[blodefood]

I've seen a brand name oven that uses a similar method of baking with tealights. The one advantage of your system is that the tealights are spaced out instead of grouped closely together. Close grouping make the tealights prone to flash fire. The wood box, to me, is a little frightening because of fire but it does have insulating properties that the metal box construction of the brand name oven doesn't. To borrow an idea from it though, you might try adding some sort of flat stones that will retain the heat after the candles have gone out. It could give you potential for extending the cooking time as well as releasing heat into your camping abode on a cool night when the cooking is done. If the stones are removable, you could heat them in the sun or on a fire and insert them into the box at the start of cooking time. Great edible 'ible! :-)

[PaulS69]

From a safety perspective and to also increase the internal temperature, some roof slates lining the inside of the box might be useful. Obviously you'd need to drill holes for ventilation

[mary.beheler]

One caution: Kidney beans (and to a lesser extent, others) contain a toxin that can be destroyed with 10 minutes of boiling soaked beans, but becomes 5 times more potent if cooked at 80 degrees C. The effects can be quite unpleasant, even deadly. It would be wise to make _sure_ beans reach a temperature that destroys the toxin.
I have seen a few posts that say slow cooking beans at 85 degrees C is safe, but I'm not sure how long they would need to stay that hot. However, soaking beans overnight, discarding the soak water, then boiling them for 10 minutes could be done even when a thermometer is not available.
The toxic agent is Phytohaemagglutnin (Kidney Bean Lectin)

http://www.foodreference.com/html/artredkidneybean...

[PaulS69]

In fairness, if you're going off grid you'll surely pick your meals to suit your equipment and being off grid, safe storing of meats isn't going to be practical for any length of time so it's more practical to stick to vegetarian recipes anyway. If you're making a vegechilli then canned kidney beans or just leaving them out is the way to go.

[Kevanf1]

Being as this Instructable is about an off grid 'slo cooker' maybe using kidney beans is not such a good idea. I'm just thinking that at higher altitudes (which if you are off grid you could find yourself in) water boils at a lower temperature. Go high enough and you certainly cannot make a decent cup of tea even though the water is boiling. I imagine that cooking kidney beans in water at a higher altitude could end up with the beans simply not being brought to a high enough temperature for the same reason. I have to admit that this is not something I have thought of before and it only sprung to mind after reading the very sensible warning from 'mary.beheler'.

[rgbarnes]

At high altitude we cook with pressure cooker to address the problems. Heating the pressure cooker on a stove or open flame until pressure is reached, than using the box to maintain the temperature would work perfectly. We have to lower the temperature anyway, even if the cooker is on stove top or other heat source.

[spoesse]

Your method may be safer as in wont catch fire but it wont safer food poisoning wise, especially when cooking meat. You cant slow cook meat without heat.

[rgbarnes]

But you can use low heat and long cooking times. See sous vide cooking.

[bobwojo]

I can verify that this is true, My wife tossed some into her rice cooker with the rice and got very ill. Luckily she only ate a small number of the beans, prob less than 10.

[Krimlar]

Thank you for posting this.

Unless you are trained in the medical field, or a professionally trained Chef, you would not know this.

You also need to discard the soaking water, and not cook the beans in it; also change the cooking water at least once.

Also, adding salt will keep the beans skins tough, if you want to keep the texture similar to "raw" beans for a salad, or just like that texture.

I prefer this texture in almost all my dishes.

[meddler]

I wan't to try to adapt this to work with a rocket stove pipe.

[Lorddrake]

This is a really interesting idea.

as far as the concern about the kidney beans .. just use the canned kidney beans .. they are fully cooked in the can as part of the canning process so you don't have to worry about toxins.

One addition I would make is a metal plate with feet in the bottom of the box. make it tall enough to clear the candles, and the pot can sit right on top of it. It will serve 2 purposes 1) it will collect most if not all of the soot from the candles so your pot stays clean. 2) it will act a dissipater to more evenly spread the heat along the bottom of the pot and reduce "hot spots"

[ex811]

Not to be too critical, but the mixing of metric and imperial measurements is a bit confusing to some of us in America. But I love your idea and this is a good write-up.

[Wild-Bill]

It is easy to convert from Celsius to Fahrenheit. 100C is 212F and 0C is 32F so Multiply degrees in Celsius by180 and add 32 will give you degrees in Fahrenheit. Though not highly accurate, say there are 2.5 centimetres to the inch. These conversions I do in my head without thinking about them, but then I am from Canada and we switch both Imperial and Metric all the time.

[Lorddrake]

1.8 not 180

[Pixiedust7]

Except that it's not easy, because nobody ever remembers this!

[al_packer]

It's real easy; I just punch in the measurement in one scale on my ancient Palm PDA and tap for the result in the other scale. That leaves lots of room in my brain for really important stuff like the latest scandal involving whatever celebrity.

[bobwojo]

Anyone involved in Engineering or any Science will never forget the formula it is used so much. For everyone else I agree. .