Distilling specialists at Heriot-Watt University’s International Centre for Brewing and Distilling have been working with the Black Cat Pub and Folly Spirit Labs to turn surplus bread into a drinkable spirit.
Professor Annie Hill and Dr Kelly Stewart supervised two Heriot-Watt students who grew three types of koji mould, white, black and yellow, directly onto slices of waste bread. The mould’s enzymes converted the bread’s starch into sugar, which was then fermented into alcohol using yeast, the university said.
The project was started by Chris Miles, owner of the Black Cat Pub, who already makes a fruit spirit called Pochle Geal from surplus apples gathered around Edinburgh. He said a conversation with a food bank manager about unsold bread led him to approach Professor Hill for help developing the idea, after he began thinking about koji’s role in making sake and other Asian spirits.
The team has now chosen one sample from its initial trials to take forward. Miles said: “The one we want to take forward smells a bit like the crust of Mother’s Pride and tastes more like the middle of a sourdough.”
He said he could see it being used as a cocktail base or mixer, adding that bars in the city were looking for more sustainable products, and that some of the spirit would also be aged in casks.
Professor Hill said the approach was notable because it used a waste material rather than an expensive raw ingredient as the starting point for a high value product. She said around one million loaves of bread are thrown away across the UK each day, and that further work was needed to establish which types of bread and koji cultures produced the most consistent results.
Miles said he ultimately hoped surplus bread and pastries from local cafes and other businesses could be collected to be turned into what he described as a flagship spirit for Edinburgh, diverting the waste from landfill.
A Heriot-Watt postgraduate student is continuing to study other fermentation methods as the partners consider how the process could be scaled up for commercial production, the university said.