‣ By following the wisdom of nature, waste becomes growth  

“There is no waste in nature”, said Florian. "A dead twig is a source of nutrition for something else. It's weird that we as humans create waste and simply burn or bury it. We can use our raw materials so much more efficiently by following the processes of nature." 

Traditionally, mushrooms are grown on imported materials like straw, wood chips, or special mixtures of sawdust and agricultural waste. But Rotterzwan thought differently: why not use what we already have right here in Rotterdam? And they came up with coffee grounds, a waste stream of 200 million kilos per year in the Netherlands only.  

Instead of throwing all that into the bin, they turned it into fertile ground for oyster mushrooms. Suddenly, yesterday’s latte became tomorrow’s lunch.  

‣ By closing the circle between waste and food 

Rotterzwam partners with cafes, offices, and even hotels like The Usual to collect their used coffee grounds. In return, those same partners serve delicious oyster mushroom snacks made from the harvest. The loop closes, and the city becomes a little bit greener. 

And it doesn’t stop with coffee. Rotterzwam works with local partners like Kaapse Brouwers (the local beer supplier of The Usual), reusing brewers’ grains from beer production. They also help other cities set up similar mushroom farms. “We don’t compete,” Florian says, “we share knowledge. It’s about the bigger picture.” 

‣ By challenging the rules that hold innovation back

Bringing this type of innovation always holds some challenges. For years, growing mushrooms on coffee grounds wasn’t even legally allowed, so regulations considered it “waste”. It took patience, persistence, and four years of pushing before the rules were updated.

‣ How are mushrooms a healthy addition to our diet?

Beyond their role in tackling waste, mushrooms are also underrated superfoods. They’re packed with nutrients, support the immune system, and even protect against diseases like Alzheimer’s. Just 100 grams a week can make a huge difference to long-term health.

Rotterzwam sees them as more than food. They’re tiny bioreactors, capable of transforming waste into value, health, and new opportunities. And the beauty is, anyone can try it. Even a bag of coffee grounds at home can become the start of your own little circular farm.