Edible cement

Food waste, if not composted, is one of the worst contributors to greenhouse gases, as it decomposes into methane. So Tokyo University’s new research into using food waste to make cement offers an innovative way to sequester all that carbon, and – perhaps – create some tasty buildings.

The problem of food waste

Food production is a complicated business that entails an enormously convoluted supply chain, each link of which affords an opportunity for ‘shrinkage’ or – to be more candid – waste. It is estimated that approximately 40% of the food produced in and/or imported into the United States is wasted – much of it perfectly edible. A 2011 UN Food and Agriculture Organisation (FAO) report estimates that – worldwide – about one third of all food produced is not eaten, and most of that ends up in landfill. To bring this closer to home, a 2017 study by the Worldwide Fund for Nature (WWF) reports that about 10 million tonnes of food (a third of our total production) goes to waste in South Africa every year.

Food waste has many causes. Farmers may not bother to harvest crops if the market price is less than the cost of getting the food to market. Packing sheds discard fruit and vegetables that are irregularly shaped or do not conform to standard sizes. And the supply chain is so long that there is, inevitably, wastage and spoilage on the long trip from farm to fork.

Supermarkets discard food when it reaches its sell-by date and – yes – we all buy too much food and toss it away when it’s less than perfect. Go check your fruit bowl now. Is there an apple or banana that looks less-than-delectable? Chances are you’ll toss it, and buy a new, fresh one.

What can be done with food waste?

Well, clearly the best thing to do with excess food is to somehow ensure that it gets to hungry people, but – bizarrely – that is not as simple as it sounds. The next best thing is to ensure that it enters the nutrient cycle efficiently by either feeding it to animals or composting it. And the next best thing is to use it constructively. The very worst thing to do with food waste is to let it go to landfill, where it forms a smelly, slimy, decomposing source of greenhouse gases.

Concrete from food waste

Of course, the thought of making concrete from perfectly edible food is quite bizarre, but there is sufficient not-optimally-edible food waste from the canning and food manufacturing industries to make this concept worthwhile. So the breakthrough by Tokyo University’s Institute of Industrial Science could go some way towards mitigating the problems associated with decomposing food waste, as well as the huge amount of CO₂ produced in manufacturing concrete in the conventional way.

The researchers subjected various types of vegetable waste to a heat press similar to that used to make construction materials from wood waste. They started off with seaweed, cabbage leaves, and orange, onion, pumpkin and banana peels. Except for the pumpkin, these all produced a material that was stronger than concrete. ‘Our goal was to use seaweed and common food scraps to construct materials that were at least as strong as concrete,’ says Yuya Sakai, the senior author of the study. So far so good. But then he adds: ‘Since we were using edible food waste, we were also interested in determining whether the recycling process impacted the flavour of the original materials.’ And, interestingly, they found that it did not.

They even added seasoning to the mix of powdered vegetable waste and water that went into the heat press, and came up with a cement-like substance that ‘retained its edible nature, and the addition of salt or sugar improved its taste without reducing its strength.’ It also proved resistant to rot, fungi and insects even after exposure to air for four months – and ‘with no appreciable changes in appearance or taste’. What is more useful, though, is that the material also retains some of its colour, producing a range of delicate pastels that could be used to great effect.

Why?

Clearly, using food-processing waste such as peels and cores as a feedstock for the production of a concrete-like product is a good idea. But, as I entertain visions of Hansel and Gretel being lured into the witch’s cottage, and ponder the implications of being literally ‘eaten out of house and home’, I can’t help but wonder why the researchers chose to retain the taste and ‘edible nature’ of the original feedstock. I can only put it down to the fact that – as true researchers constantly pushing the boundaries of human knowledge – they could not resist the challenge. So, regardless of what this material tastes like, it might well turn out to be a sweet solution to at least one aspect of global climate change.