Review: Save energy on cooking with Wonderbag

I have been testing a new product which reduces the energy required for cooking by insulating a hot pot so it continues cooking when you take it off the stove. The product is Wonderbag by a South African company, Natural Balance. The bag is made with a poly-cotton fabric and stuffed with insulating polystyrene balls. Natural Balance makes the bags in a poverty alleviation project, so there is a second benefit.

I decided to try it with a curry, and I included chicken, vegetables and potato in the mix to test how well the various items were cooked. Being in a bit of a hurry, and keen to really test the system, I reduced the Wonderbag recipe book 20 minute cooking time to around 15 minutes before transferring the pot to the Wonderbag. Six hours later we opened the bag to eat our curry dinner.

The ingredients

Getting started on the stove

In the bag

Opening the pot

Dinner

The result: The curry was delicious, and it definitely took less energy to cook than the normal stove-top-only method. Larger chunks of potato were still a bit firm, while smaller ones were well cooked. I think I did not allow enough time for the big chunks to heat through before transferring to the bag. After 6 hours the food was still hot enough to serve, but any longer and I would recommend some reheating or microwaving.

While the hot pot was nestled in the Wonderbag, I noticed that the sides and top of the bag were not warm to the touch, but the base was slightly. This means that the main source of heat loss was conduction (down), not convection (up).

I liked: The bag accommodated my big pot easily. It definitely saved energy as promised. Preparing the food in advance means that dinner is ready whenever you are, so it is great for guests. It can be a great way to make padkos that will be ready when you arrive at your destination. Many foods, like stews and curries, taste better with time for flavours to permeate. The bag lets you handle multi-dish meals with limited number of hotplates. Another use for the bag is to keep plates warm while the oven is busy.

Limitations: The bag is quite big to store in the kitchen. I am not sure I will always have time/energy to prepare supper before leaving for work in the morning – I can see it working on the weekend though. Cooking probably stops at 2-3 hours as the temperature drops from 100°C when it was being boiled. This limits the total energy savings for a pot of food, and also limits the benefits at altitude.  It would be interesting to experiment with bagging a pressure cooker (15 psi or 120°C), but ours is too big.

The verdict: It has definitely earned a place in our kitchen.