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Bulk tank cooling and storage vs. direct tanker loading

Mark Wehr Published on 29 October 2012

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In the past several months, there have been several articles published in Progressive Dairyman about direct tanker loading (DTL) of milk at the dairy farm. The third article in the series concluded with a suggested discussion topic concerning the use of silos and chillers for milk cooling and storage.

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This article will look at several possible cost-saving advantages to this system that dairymen should consider when expanding or building new facilities. Every farm is different with different circumstances, so some considerations will have more significance than others on individual dairies.

As was pointed out in the DTL articles, initial capital costs are only one aspect of overall milk cooling cost and may not be as significant as some ongoing costs of milk cooling, storage and hauling. Also, costs imply direct monetary amounts. However, cost considerations do include some value judgments that have indirect or secondary costs.

As an example, a second back-up compressor on the bulk tank may only have a value in terms of piece of mind until it is needed and a tank of milk is cooled and sold rather than dumped in the lagoon. At that point a real monetary amount can be assigned to the second compressor. With these primary and secondary costs in mind, what is the least-cost method of milk cooling, storage and hauling?

Generally, dairies smaller than 600 to 700 cows need not consider any system other than milk cooling and storage in a bulk milk tank for the following reasons:

1. Direct expansion freon cooling of milk is the most energy-efficient.

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2. The evaporators and refrigeration units on a large milk cooler can handle the milk cooling load from a dairy of this size. A chiller is not a requirement.

3. Fill time for a DTL system is too long on this size dairy, resulting in too much heat gain in the tanker.

Dairies in the 700- to 1,400-cow range probably fit the DTL system best. Depending on milk production and milking facilities, these dairies may exceed the cooling capacity of the bulk tanks. Dairies of this size often require a chiller.

The fill time for a DTL system would be acceptable (18 hours or less – 24 hours maximum.) The amount of milk produced would not require more than three truck bays with two trucks on site.

Are the costs different for dairies larger than 1,500 cows? Is everything the same, just bigger and more of it? Milk silo storage has several possible advantages. The advantages will differ for each individual dairy and some will have more importance to one dairy than another.

Initial cost always seems to be a big factor. Although one of the main points of the previous DTL articles is that capital cost is not as big of a factor as many perceive, capital cost must be combined with ongoing operating cost when comparing DTL with silo storage.

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The cost of a silo is comparable to the cost of one over-the-road tanker. However, a silo can hold two or three tanker loads of milk. Over-the-road tankers make expensive storage vessels when they are sitting at a dairy. They were designed and built to be moving milk. As dairies get larger, more trucks are needed on-site because the time decreases to fill each load. More trucks on-site plus the trucks on the road moving milk increases the cost of storing and hauling milk.

The time window is another advantage of silo storage. A large dairy filling a tanker every four to six hours cannot comfortably operate with a two-truck, three-bay DTL setup. The time window does not allow for a truck breakdown, scheduling error or inclement weather.

Two multiple-truck storage silos would have the same approximate cost as the two-truck, three-bay DTL setup but have at least twice the time window for milk pickup. On-farm silo storage can have the advantage of lower hauling costs if milk plant deliveries are a factor in some market areas.

Weekend and holiday deliveries increase wages and in turn processing costs in some markets. On-farm silo storage can reduce weekend and holiday deliveries. Hauling costs can be lowered for the dairy with adequate on-farm storage that helps alleviate weekend and holiday milk processing bottlenecks.

On-farm silo storage has the advantage of maintenance cooling or limited backup cooling available. DTL systems have no provision for even a minimal chiller malfunction.

As was emphasized in the previous articles, hauling costs are very difficult to pin down. There is no free hauling. All aspects of milk storage and hauling have costs. Who pays those costs and whether the costs are visible or hidden does not eliminate the costs. Wash water and chemicals are real costs.

Time is money. The time required for milk truck loading from on-farm storage is a cost that has to be weighed against the time to hook and unhook trailers in a DTL system.

In some parts of the country, tandem tankers are utilized for large dairies. However, backing tandem trailers up to a milk barn is not an easy task. Is a DTL system even a possibility for these dairies? Can a pull-through DTL system be designed to meet inspection requirements?

An often-discussed point related to milk storage is milk ownership. High-quality milk does not have to hunt for an owner; low-quality milk is another matter. A common thought process is that DTL milk ownership is transferred when it is pumped on the trailer at the dairy.

However, there have been occasions when dairy farm ownership has been extended to points far down the milk marketing chain when poor-quality milk is involved, regardless whether the milk shipped was DTL milk or milk from on-farm storage. If the dairyman has the liability of milk ownership, shouldn’t he physically have possession of the milk in on-farm storage where he can control the quality for as long as possible?

Dairymen must consider these and many other points and counterpoints to consider when making milk cooling, storage and hauling decisions. PD

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Mark Wehr

Regional Manager
Dairy Farm Equipment
Paul Mueller Company

PHOTO
An often-discussed point is milk ownership. High-quality milk does not have to hunt for an owner;
low-quality milk is another matter. Photo by PD staff.

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