Bringing the temperature of milk down to 6C in two hours would be a massive jump for some existing milk cooling plants, Craig Gibbons, general manager of sales for Tru-Test’s DTS Milk Cooling and Tank Solution, said.
“It doesn’t sound that much but you’re asking for the refrigeration to be a lot more efficient.”
The practical consideration onfarm was to get milk even colder in the vat, as a risk buffer, so it could be cooled to less than 6C.
“The requirements will vary farm to farm,” Gibbons said. To help assess what was the right solution for each farm situation, they offer onfarm audits of milk cooling systems.
“The solution could be simple as checking your plate cooler to ensure the right water flow and number of plates are correct,” Gibbons said.
Ideally, there should be about a 2.5C difference between the temperature of the water entering the plate-cooler and the temperature of the milk exiting it. If the difference was greater, more plates might need to be added, or the milk or water flow adjusted.
“Depending on your water source, the milk could be entering the tank anywhere up to 30C. In instances where the milk is entering the tank at a high temperature and your vat refrigeration is already at its maximum capability, you may need to invest in a pre-cooling system.”
He said that in most instances new dairies would have already installed more efficient milk cooling systems as part of the project. However, most farm dairies did not have water pre-cooling and instead relied on the refrigeration unit in the vat to bring down the milk temperature.
“Every farm is different. Bigger refrigeration on the vat may cost $8000-$15,000, a large glycol system can cost up to $80,000 installed, and a cold-water or ice-bank system may be around $40,000.”
Craig said more farmers had become aware of their milk cooling requirement since Fonterra started rejecting milk for not meeting the cooling timelines.
Supply Fonterra technical programme manager Karl Rossiter said he wanted farmers to get their milk cooling systems evaluated.
“There may not be a big cost to this. An upgrade could be as simple as resetting pre-set points on chiller units or water flows through a primary cooler.”
He said he was keen on industry collaboration so that farmers could be fully informed.
“Hopefully we can identify farmers who have upgraded their refrigeration and invite others along to look at the options.”
There were four main options for pre-cooling water to be used in plate-coolers: cooling towers, ice banks, instant chillers, and thermal stores.
Cooling towers worked through evaporative cooling, and well-designed systems could get the water cooled to within 5C of the wet bulb temperature, but weren’t very effective in areas of high humidity. Fan-forced systems had the potential to turn over large stores of water every hour and usually operated overnight.
As the name suggested, ice-banks generated ice along evaporator coils overnight with the ice used to chill the plate-cooler water.
Snapchill, which recently opened a factory at Foxton, has designed an ice-bank system which made ice using off-peak power, to be stored in an insulated tank until used, with milk chilled to 6C before it enters the vat.
Snapchill owner and sales manager Matt Parkinson said the 80C hot water generated through a heat recovery system could be used for plant washes, saving costs associated with cylinder hot water heating. Milk entered the vat at such a low temperature the vat’s refrigeration unit carried a much lighter load.
Instant chillers didn’t rely on stored water, but chilled the water as required through a food-grade glycol-water refrigeration system. They had a lower water demand and operated on-demand, such as during milking.
Thermal storage systems were based on an insulated storage tank that held one day’s milking volume of water, using off-peak electricity to chill it. Unlike the cooling towers, thermal storage systems actively chilled the water rather than relying on evaporation.
