A Cool Way to Chill Milk

Published: Sep. 10, 2013

By Harish Damodaran for The Hindu BusinessLine

In 2013,
Promethean Power Systems
(United States) received a Powering Agriculture award for the
Market Growth (Stage 5) of
Energy Efficiency
Solar Photovoltaic
solutions for
Cold Storage
in the production of

There are few better sources of wholesome nutrition than milk straight from a cow’s or buffalo’s udders.

But the sheer time taken for milk from the udders to be collected at a centre and transported to a dairy or chilling plant—roughly four hours—translates into significant loss of freshness and aroma. The shelf life of the milk is lower even after pasteurisation, while boiling depletes its original nutritional value.

As a solution, many dairies of late have sought to get the milk chilled at the procurement centres itself.

Chilling basically stunts the growth of bacteria converting the lactose or sugar in the milk into lactic acid, which curdles the proteins and causes souring. It should be done within one/one-and-half hour of milking, after which the naturally occurring preservatives in the milk (including carbon dioxide) stop working.

Cooling in Bulk

Dairies now use bulk cooling tanks to chill their milk to about 4 degrees Celsius at their procurement centres. These tanks, of 3,000-5,000 litres capacity, keep the milk chilled till the tanker from the dairy arrives.

But the coolers have three major drawbacks, according to R.G. Chandramogan, Chairman and Managing Director of the Rs. 2,200-crore Hatsun Agro Product Ltd, that procures an average 20 lakh litres of milk a day. The first is the capacity. While 3,000 litres is what an American or European dairy producer supplies daily—making it viable to have a cooler even at the farm itself—his average Indian counterpart barely delivers 10 litres. “Forget individual farmers, even our procurement centres handle less than 1,000 litres each. So, you operate the bulk coolers at suboptimal capacity,” said Chandramogan.

Second, given irregular power supply in rural areas, the bulk coolers require the back-up of a diesel generator set.

That again raises costs—a 5,000-litre cooler with generator set and other installations comes at Rs. 9 lakh or so—besides causing noise and air pollution. Third, the bulk coolers take 3-3.5 hours to chill the milk to 4 degrees. There is no instant chilling here, more so with many farmers pouring one after the other milk at ambient temperatures. Real chilling happens only when the pouring stops.

Solar chilling

Given these problems, it was natural for Chandramogan to be interested in a solar-based ‘rapid milk chilling’ concept floated by Sorin Grama, an electrical engineer from Massachusetts Institute of Technology, and Sam White, who had worked in various start-ups at Boston.

What they had in mind was a thermal battery that could use stored electricity from the sun to reduce the temperature of a liquid coolant to sub-zero.

The battery would also have a compressor to pump the coolant—a proprietary solution having a freezing point below that of water—through tubes to a separate cylinder-shaped chilling unit.

The milk collected from farmers is poured on top of the cylinder, maintained at about minus 3 degrees by the circulating fluid.

As the milk goes over the cylinder at a flow rate of around 200 litres an hour, it gets chilled and conveyed to an insulated storage silo.

It can remain chilled there for up to 12 hours. What this entire system essentially aimed at was to decouple the supply of power from chilling:

The battery would get charged whenever electricity from the sun was available, while the refrigeration cycle operated independently.

Concept to implementation

“I liked the idea, even though such a system hadn’t been installed anywhere. I offered to fund it, including the cost of installing it at my Karumapuram dairy here”, recalled Chandramogan. Grama and White spent all of 2010 designing and building their rapid milk chilling system in Boston. This they shipped out for installing at Hatsun’s plant in February 2011.

But Chandramogan wasn’t really impressed with what he saw. “Although it chilled effectively, the equipment with all its solar panels occupied some 300 sq. feet, which was almost like opening a new procurement centre,” he said. Grama and White eventually dispensed with the idea of solar-powered milk chiller.

Instead, they developed a new thermal battery that could store electricity even when available for 12 hours daily and release that energy to run a refrigeration cycle.

They also designed a more compact system capable of storing extra thermal energy in lesser space. The earlier 2,000-litre solar battery could chill only 500 litres of milk. The present 500 litre battery can chill 1,000 litres.

Hatsun Agro has already installed three rapid milk chillers—each costing Rs. 5 lakh—and placed orders for another 50 from Promethean Spenta Technologies, the company founded by Grama and White.

“We are also supplying to Amul, Nestle and Heritage Foods,” said Grama, who is working on adapting the same energy storage technology to other cold-chain applications in power-deficit rural environments.

The basic technology concept in this case may have come from Boston and MIT. But the credit for making it work on the ground probably goes to Hatsun Agro.

“We wanted a chilling system that could work without continuous electricity and generator sets, while factoring in our realities of collecting milk from thousands of small producers.

That objective has been served,” Chandramogan said.

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