In an era where the message of “every person for themselves” seems to be the rallying cry of more and more political manifestos and empathy for those less fortunate than ourselves is on a downward spiral around the world, what are the chances of an inventor creating a product with a worldwide potential market – and then refusing to patent it so as to allow it to be reproduced as widely as possible? Seems like a fairy tale, doesn’t it? And yet that is exactly what South African Sarah Collins did when she developed the Wonderbag™, a heavily insulated cloth container that functions as a non-electric, easily portable slow cooker that is perfect for slow cooked recipes like my beef in Guinnes stew or oxtail in red wine.
Sarah Collins grew up in Kwa-Zulu Natal, South Africa and it was through her work with communities as an anti-apartheid and environmental activist that she realised that impoverished and often rural sub-Saharan communities faced a complex combination of challenges including dependence on fossil fuels because of power shortages; poor air quality and safety concerns in and around the home created by cooking over woodfires; and women having limited opportunity to pursue education or careers because looking for fuel and cooking remained such time intensive activities. Inspired by a cooking method (similar to a haybox) that she had seen in her grandmother’s kitchen in the 1970s, Sarah started experimenting. To her surprise, she discovered that if she removed a boiling pot of food from the stove and surrounded it with cushions, it carried on cooking for several hours without fuel. She was spurred on to develop the idea by the start of “loadshedding” or rolling power cuts in South Africa in 2007 and she founded Wonderbag™ in 2008. Once she had a few prototypes, Sarah started taking the Wonderbags into communities to see first-hand the impact they could have, and women’s reaction was overwhelmingly positive.
“It’s a simple idea, but it addresses so many interconnected issues— from climate change to gender equality”, says Sarah and she knew immediately that her simple idea had the potential to change lives around the world. Global record energy prices and soaring carbon emissions are placing significant financial pressure on households, and our planet. 2.5 billion people still cook over an open fire each day, causing significant emissions and respiratory issues; widespread deforestation; and burdening women with hours of unpaid labour. But what is the Wonderbag™? It is an incredibly low-tech solution to these problems, consisting of a pumpkin-shaped double-walled drawstring cloth bag with re-purposed foam insulation between the cloth walls. Once food (think meat stews, vegetables, rice or pulses) have been brought to a boil using a fire or stove, the pot is placed immediately into the Wonderbag™ which is pulled tightly shut to insulate the pot and then left to cook at a lower temperature for anywhere from 2 to 8 hours. This allows families to continue cooking daily hot meals even without a regular power supply, and frees women to stay in education or employment as family meals can be prepared in advance and safely left to cook while they are at work or their studies.
Other than providing a nifty low-tech cooking innovation, the Wonderbag™ also has impeccable social and environmental impact credentials. Each year, one Wonderbag™ can cut a home’s cooking fuel usage by an astonishing 70 percent; save five trees from being cut down; and reduce carbon emissions by one tonne. This is in addition to other major benefits such as female empowerment, job creation, and significant cost savings for families. Wonderbag™ has also helped increase the income of an estimated 500,000+ women across 20 countries, many of whom sell or make the bag, or use it as part of their catering businesses. They even consider the impact of their global shipping – each bag is shipped as sustainably as possible by shrink-wrapping it to drastically reduce parcel size. It’s no surprise that Wonderbag™ was named one of TIME Magazine’s 50 genius companies of 2018 and that it was the main focus of a 2024 article in Forbes Magazine about sustainability and food security.
But maybe even more importantly, the Wonderbag™ has had a huge social impact on communities in crisis around the world. Back in 2018, the company partnered with the Red Cross to bring Wonderbags™ to refugee camps in Uganda and Rwanda. In South Sudan and Uganda, where refugee camps are often overcrowded and firewood is limited, Wonderbag ™ have eased tensions between refugees and locals over scarce resources. Wonderbags™ have also been distributed in Ghana, Jordan, Malawi and of course South Africa. In 2022 over 2,500 Wonderbags™ were donated to two NGO’s in Ukraine supporting families during the war with Russia. The Wonderbags™ were sent from the company’s UK warehouse and were distributed to families fleeing from war-torn areas, such as Mariupol, as well as families who remained in Ukraine but had limited access to gas and electric for cooking. Wonderbags™ are deployed in Gaza, where energy infrastructure has been decimated by the war. When the conflict began, Collins established a sewing group in Cairo and sent finished products across the Egyptian border in collaboration with World Central Kitchen. Although at the time it was prohibited to send cooking fuel into Palestine, the innocuous pumpkin-shaped cloth Wonderbags™ were allowed trough unimpeded. So far over 6 million Wonderbags™ have been deployed in communities, especially in rural areas and conflict zones.
As the Wonderbag™ is essentially a slow cooker that requires no power, it is best suited to recipes that require long, slow cooking – so this was the perfect opportunity to try out a comforting winter warmer stew. This recipe for a Japanese-inspired beef stew by first appeared on the New York Times and I adapted it for the Wonderbag™. There is an excellent FAQs section on the Wonderbag™ website, but some tips worth noting here are:
- food needs to be brought to the boil over a conventional heat source and boiled for at least 15 minutes before putting it into the Wonderbag™
- you can use pretty much any kind of pot – copper, steel, aluminium, cast iron, enameled cast iron and tempered glassware. I used enameled cast iron on the basis that cast iron retains heat exceptionally well and this worked brilliantly.
- a pot with short handles and a tight fitting lid works best.
- place a wooden chopping board, trivet or folded tea towel in the base of your Wonderbag™ and place your hot pot on top of it so as to prevent the interior fabric from getting singed.
- transfer your pot to the Wonderbag™ as quickly as possible once removed from the hob and resist peeking during the cooking time. This helps to ensure the temperature of the food stays as high as possible during the Wonderbag™ cooking process.
- the Wonderbag™ can continue cooking food for up to eight hours, and keep your food warm for several hours after this – see their handy cooking time guide for more details.

Why not try some of my other beef recipes:
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This slow cooked beef stew with its Japanese-inspired flavours can be made with or without a slow cooker - or even in a Wonderbag™!
- 0.75 to 1 kg boneless braising/stewing beef cut into 2.5-4cm chunks
- 1 Tbsp sunflower oil for searing
- 500 ml chicken stock or dashi stock
- 60 ml light soy sauce
- 60 ml honey or mirin (rice wine)
- 10 slices peeled ginger root, about 2cm in diameter
- 1 clementine or small orange
- 700 g peeled butternut squash, pumpkin or sweet potatoes cut into 2.5cm chunks
- salt and black pepper to taste
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Heat the of oil in a large pan over medium-high heat, sear the meat until nicely browned on all sides side, about 5 minutes. Transfer chunks to a medium-size casserole with a tight-fitting lid.
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Add the stock to the pan and cook over high heat, stirring and scraping until all the solids are integrated into the liquid. Remove from heat, mix in the soy sauce and mirin/honey and pour over the beef in the casserole together with the ginger. Peel the clementine/orange, add the peel to the casserole. Juice the fruit and reserve the juice
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Bring the casserole to a gentle boil on the hob and allow to simmer for at least 15 minutes. Add the squash, mix, close the lid and then remove the casserole from the heat.
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Place a heatproof trivet in the base of your Wonderbag™ or a couple of folded tea towels. Place the sealed pot on top of the trivet/tea towels, cover with the insulated Wonderbag™ "lid" and pull the drawstring as tight as you can to seal the bag.
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Allow to cook in the bag without opening for at least 2 hours - but the longer you leave it the more tender it will be. (On average, even after 5 hours in the Wonderbag™ the temperature of the food is still 70C so you can easily start it before work and come home to a cooked meal.)
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When you are ready to serve, open the bag and remove the pot - be careful, mine was still too hot to touch! Salt as necessary and stir in the reserved juice.
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You can serve immediately, but as I wanted the sauce a little thicker I stirred in a little cornflour/cornstarch mixed with water before serving in bowls over brown rice.
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Bring to the boil on the hob (or in a 180C oven) and leave at a steady simmer for at least 30 minutes, then stir. Check approximately every 15 minutes and stir so that it does not stick.
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When the meat is nearly tender enough (about 45-60 minutes), stir in the squash and continue to cook for 15-20 minutes until the squash is tender but not mushy.
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Remove from the heat, add salt if necessary, then stir in the citrus juice and serve in bowls over brown rice.
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