Wonderbag, insulation and steam


As  part of the Kenya workshop, we took a Wonderbag and demonstrated it with cooking rice.  Surprisingly Wonderbag don’t yet have a representative in Kenya although Practical Action have tried a similarly principled product (which we understand is struggling in the market).  PA call it a fireless cooker.  (And its not a new idea – in UK we used to have the haybox)

Both these products pick up on the idea that it is not energy that cooks food but temperature.  If one raises the cooking pot to a temperature that will cook and then keep it there, the food will cook.  Traditionally we heat a pot, and then add more energy to keep its temperature up.  We simmer the food by adding more energy.  We only have to add energy because we generally allow energy from the pot to dissipate and ‘disappear’.  The loss of radiant heat cools the pot, so we add energy to keep the temperature high.  The Wonderbag and the PA fireless cooker counter this by suggesting that the pot be moved from the cooker into a basket or bag that is thermally insulated.  This means that the food remains at a high temperature, and cooks.

Slow cookers use the same principle, using a small amount of energy to bring the cooking space up to temperature, and then using insulation and minimal extra energy to keep the temperature high while the food slowly cooks.

Our colleague Rezwan Khan from UIU, uses this principle in his 300W solar electric cooker prototype.  In Kenya he demonstrated that with insulation he was able to cook rice in almost the same time as our 1kW hotplate (my pride suggests I should emphasise ‘almost’).  In our cook off we raced to cook the rice, and the total energy used for Rezwan and ourselves was almost the same.

So why then don’t all pots and pans come with insulated walls?  I think the answer lies in two thoughts.  First – with charcoal burning so much energy is wasted going up the sides of a pot that it wouldn’t be worth doing (and hence the reason both Wonderbag and PA fireless cooker suggest taking the food off the cooker and putting it into insulation – and I assume using the remaining charcoal to cook something else or to be put out.)  Second the savings when applying this to electricity and LPG can be relatively small and most people using electricity and gas no longer care about the pennies.  My colleague here in the UK  complains that his wife doesn’t even use a lid during cooking – but to be fair to her, how many of us do and do we think it would make a significant difference to our electricity bill?

As we enter new territory where the poor are going to be cooking with modern energy, and where every saved kilojoule is precious saved money, then insulation is likely to become very important.  Remember, the Nottingham students who explored this could save 60% of their energy by extreme insulation.  It was a bit clumsy but it reflected the potential savings of the Wonderbag.

One last thing – I put in the title ‘steam’.  My colleague Rezwan makes one more suggestion.  From an engineering point of view he notes that a huge amount of energy is lost when water converts to steam (and Mrs Scott, this is why lids are important).  As an engineer he suggests that water could be brought to 98 degrees C, and then held there.  His point is that when water is boiling at 100 degrees it is at 100 degrees – it never gets to 105 degrees.  He reasons that having water blasting away boiling and creating steam is not really increasing the cooking environment (temperature) for whatever is in the pot.

So in his prototype he shuts down the energy input when a sensor tells him his pot is at 98 degrees.  This is potentially a considerable saving in energy – but would it be acceptable to people – to not boil the water?   Supposedly coffee tastes better at 70 degrees, and my kettle at home offers me settings which are 70, 80, 90 and 100 – but it feels odd to make coffee without boiling the water and so I always hit the boil button.  I think Rezwan is exploring a considerable challenge – not a technical one– restricting the energy flow is easy with modern energy, but in terms of behaviour change.  Could we ever persuade people to use 98 degree water for cooking rice?

Well actually, apparently, simmering is just that.  Wikipedia states Simmering is a food preparation technique in which foods are cooked in hot liquids kept just below the boiling point of water[1] (which is 100 °C or 212 °F at average sea level air pressure), but higher than poaching temperature. To keep a pot simmering, one brings it to a boil and then reduces the heat to a point where the formation of bubbles has almost ceased, typically a water temperature of about 94 °C (200 °F) at sea level. 

And that in itself is interesting because that is at sea level.  I suddenly realised – we were in Nairobi!  Nairobi is at 5000ft so everyone who boils their water in Nairobi is actually cooking food at at 96 degrees.  I am not a food scientist and I think we should probably find one and find out the implications of cooking food at lower than boiling temperatures – but the fact that significantly large populations around the world, those living at higher altitudes, do actually cook at around 96 degrees, does suggest to me that Rezwans cooking is safe, and that there is something here to be explored further (in terms of energy saving)

Finally and in contrast to the above (but linked because its all about air pressure) perhaps an answer is more pressure, simulating being below sea level.  I know that my colleagues are also interested in pressure cookers.  I have to say that my childhood memory of pressure cookers is trying to lift up the weight and not scold yourself!  However I am told that modern pressure cookers are safer!

Anyway, maybe there is something more to be done in bringing water to heat but without actually boiling…..to be explored further.

“The Wonderbag was used by the Arctic Jubilee Expedition 2012.  Using only the expeditions ultra- lightweight camping stove and even when cooking in temperatures of minus 6°C , the food was still hot and  cooking after 4 hours!”

And a more conventional picture of wonderbag use…….


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