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Keeping the milk fresh with cow dung

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Every year, millions of dollars of milk is poured away because it cannot be kept fresh. But a series of low-cost inventions aim to change that and the lives of millions of subsistence farmers.

William Kisaalita has cold milk on his mind.

The tissue engineer runs a program at the University of Georgia in the US that develops new technologies to help farmers in his native Uganda, where he grew up on a farm.

The United Nations, in fact, estimates that 27% of all milk in Uganda goes to waste, much of it due to spoilage. The UN says that loss costs Ugandan farmers more than $20m a year. The yearly losses are similar for neighbouring Kenya and Tanzania.

So Kisaalita and his students began building a small-scale milk chiller that could hold 20 litres of the white stuff. Traditionally, big dairy machines have an outer and inner tank, with insulation in the space between. Compressors, condensers and refrigerants are pumped through the system to rapidly chill the milk and keep it cool. It?s a system that requires a constant electrical power, either from the grid or from a diesel generator back-up.

Initially, Kisaalita toyed with the idea of a solar powered device, but it was too expensive. So, instead, they turned to another product that cows produce in abundance. "A small farmer with five cows produces a lot of dung," says Kisaalita. "You can ferment the dung, and use a fraction of the bio-gas to run the milk chiller. The rest could be used for cooking or lighting."

In addition, the slurry that comes out of the bio-gas can be used to fertilize grass and crops, he says. Although on paper it looked like they had cracked the problem, Kisaalita found that farmers were not convinced that converting the bio-gas was worth the money. As an alternative, he developed a milk chiller that runs on propane, which is cheaper and widely available locally.

"My hope," Kisaalita says, "is that a farmer who starts using propane will eventually come to me and say, 'OK, this works, now build me a bio-gas version, and wean me off of propane.'"

He now has a pilot up and running in Western Uganda and continues to tweak the chiller's size and design. Right now, he's working on a 70 litre version, and trying to get the price point to around $300. He envisions a "rent-to-own" model where farmers could try out the system on a rental basis, but put money toward owning the unit in 18 months time.

"With this chiller," Kisaalita says, "the small farmer could milk her cows in the evening, chill it, and then add more milk in the morning. Then she could wait for the buyer who will give her the best price, because she's not in a hurry to sell. She's now empowered, because she knows the milk won't go bad."


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