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.

"I've always had an interest in doing something for small farmers," Kisaalita tells me. "They are my aunts and uncles, my brothers and sisters. No one develops tech to help them, but I feel that there is room to create products that improve their profitability."

Kisaalita has worked on a number of such problems over the past decade, including a low-cost nutcracker for farmers in Morocco and a solar-powered incubator for guinea fowl in Burkina Faso. But now he has turned his attention to milk producers in his home country.

Many small-scale Ugandan farmers own a few cows, which are milked twice a day to sell locally or to larger dairies. But here's the thing - for it to stay fresh, the milk has to be cooled – easier said than done in areas with intermittent or no electricity. "I've seen farmers pour their milk away at the end of the day," Kisaalita says. "Sometimes as much as half of it."  And when sour milk is poured away, so too are profits and a valuable source of nutrition.

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."

Kissalita is not the first person to try to solve the problem of keeping milk cool in soaring temperatures. For example, in 2008 a Kenyan inventor called Dominic Wanjihia showed off a gadget that he built whilst working for an NGO called Vet Aid in Somaliland. The  Fine Lined Evaporative Cooler, as it is called, is a low cost, zero-energy system for keeping camel milk cool in soaring temperatures that commonly reach 45C (113 Fahrenheit). It works by funnelling wind around a metal box lined with fabric and kept water-soaked.  As the water evaporates it rapidly cools a box in which the milk containers are placed. A big advantage of the system is that it can be made using local materials and is simple enough to be built by anyone.

Modified designs – that cost from $75 - have now been rolled out in various countries and adapted for use to store everything from milk, fruit and certain medicines. In Ghana, for example, a modified design allows the "mama mboga" – ladies who run market stalls – to display her fruit, vegetables and meats without it turning bad. “I left the system with the "fundi's" – the carpenters I had built it with - who had mega plans for mass production,” says Wanjhia. “I hope they made good their promises.”

‘Super cool’

While these projects are aimed at the individual farmer, others are going big when it comes to chilling milk. One of these is a US company called Promethean Power Systems which has its eyes on India – a country that currently produces and consumes more milk than any other country in the world.

"You have a quality issue," says Sam White, one of the co-founders. "You have to race warm milk from thousands of villages to large collection centres, twice a day. And if you don't chill milk within four [hours] of milking the cow, the bacteria grows to a point where it just goes bad."

He then stops and chuckles, admitting he never really expected to know so much, or care so much, about how milk is produced and stored in India. The start of that process began when he and his business partner won a Massachusetts Institute of Technology competition with a technology for improving electrification. In 2007, they went to India to test their business plan and that's when White and his partner, Sorin Grama, first heard about the "milk problem." They started wondering if there was a way to develop a cost-effective way to chill the milk more locally, maybe not at the level of individual farmers, but at least at the village level.

White and Grama toyed with different designs, and different technologies. Like Kisaalita, they thought about using solar power, but it proved to be too expensive, at least for now. 

After a series of failures, though, Promethean hit upon what it thinks is a viable solution. "India's electricity grid is kind of like the sun," White explains. "You get electricity every day, but it's sporadic. So, we ditched solar and started focusing on ways to capture those eight to 10 hours you get, and store it in a battery." 

But this battery doesn't store electricity. Instead, it is a thermal battery that can “store cold”. White won't go into great detail about the battery's design, except to say that it features a phase-change material that can supercool quickly in a compact space. The company recently field tested a 750 litre device with India's largest private dairy.

The cost for Promethean's chiller is around $9,000 - a good price point for bigger Indian dairies, White notes, because they are constantly looking for "peace of mind" when it comes to milk quality. He already has an order for 50 more units, albeit with some design changes. "We spent way too long building things based on the advice of venture capitalists," says White. "Now we're 100% focused on listening to what the customer wants."

The modified design incorporates a wireless device that can send employees text messages about the amount of milk in the tank, how charged the thermal battery is, and even about maintenance issues. 

The company is in the process of moving from Boston to India in the coming months and also has plans for Pakistan and some Latin American countries. It is also working on adapting the tech for beer brewers, who also have specific chilling needs for correct fermentation.

"We didn't get into this to have a scientific breakthrough," White emphasizes. "We got into this to build the cheapest, simplest solution possible."

If you would like to comment on this article or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.