How to Choose The Right Cooling Tank Capacity for Your Dairy Farm

What Is a Milk Tank

Bulk Milk Cooling Tank (Bulk Milk Cooling Tank) is a stainless steel refrigerated storage tank installed in the milk storage room of a dairy farm. It is used to quickly cool the freshly squeezed fresh milk and keep it at a low temperature until the milk tanker arrives to collect the milk.

A milk can is mainly composed of four parts: first, the food-grade stainless steel liner (mostly 304 stainless steel), which is in direct contact with the milk; second, the polyurethane insulation layer, which reduces the loss of cold volume; third, the refrigeration system (compressor, evaporation plate or ice storage jacket); fourth, the agitator, so that the milk temperature in the tank is uniform, to prevent fat from floating and stratification.In addition, it is equipped with a thermometer, sampling valve, cleaning nozzle and other accessories.The U.S. 3-A hygiene standard requires it to drop to 50 degrees Fahrenheit (about 10℃) within 1 hour and 40 degrees Fahrenheit (about 4℃) within 2 hours after milking.

The Main Factors Affecting Milk Tank Capacity

Daily milk output

This is the most basic variable.The daily milk output is approximately equal to the number of cows stored multiplied by the average yield, for example, 100 cows, the average yield is 25 liters/day, and the daily output is about 2500 liters.

Peak milk production

Cows produce the highest milk in the early lactation and forage seasons, and the peak daily output is usually 20%-30% or more higher than the annual average.The capacity must be based on the peak, not the average.

Milk collection frequency

Whether to collect milk every day or the next day directly determines how many liters of milk should be stored in the tank.To collect milk the next day, the required capacity should basically be doubled.

Single milking volume and batch

Whether the milking is divided into tanks twice in the morning and evening, and the amount of milk in a single time, will affect the mixing temperature of cold milk and new milk in the tank, which in turn affects the buffer space required.

Buffer margin

Accidents such as late milk collection trucks, vehicle failures, extreme weather, etc. require space in the tank.The common practice in the industry is to add a buffer of 20%-30% on the basis of the calculated value.

How to Calculate The Required Milk Can Capacity

There is also a simpler rule of thumb in the industry: in the case of daily milk collection, choose tanks according to 1.5 times the daily milk production.For example, Nissan selects 1,500 liters for 1,000 liters, and Nissan selects 3,000 liters for 2,000 liters. This is also the caliber commonly used by domestic manufacturers.

For example: a certain ranch has 100 cows, a yield of 25 liters/day, and a peak daily output of about 2,500 liters.If you receive milk every day, 2500×1.2≈3000 liters, choose a 3000-liter tank; if you receive milk the next day, 2500×2×1.2≈6000 liters, you need to choose a tank of about 6000 liters.

Cooling Performance

Cooling speed is a hard indicator.Our country's regulations require cooling to 0-4℃ within 2 hours after milking; the U.S. 3—A hygiene standard requires cooling to 50 degrees Fahrenheit (about 10℃) within 1 hour and 40 degrees Fahrenheit (about 4℃) within 2 hours, and after the new milk is added to the cold milk, the mixing temperature in the tank shall not exceed 50 degrees Fahrenheit (about 10℃).If the capacity of the refrigeration system is insufficient and the temperature does not drop for 2 hours when the tank is full during the peak season, the milk quality will not be up to standard.

When purchasing, focus on the "nominal cooling capacity”: the manufacturer should be able to give the time (or the corresponding cooling capacity) required for the unit to reduce the rated capacity of milk from 35℃ to 4℃.Industry specifications usually require that the refrigeration system can handle the cooling task of two batches of milk with a rated capacity (or four batches with a 50% capacity) within 24 hours. You can check whether the unit matches the tank capacity accordingly.

The blender cannot be saved.Stir to make the temperature in the tank uniform and prevent fat from floating and stratification. Uneven mixing of hot and cold milk will also distort the thermometer reading.The official Canadian guidelines require the milk storage tank to be stirred for at least 5 minutes every hour (longer if necessary), and the temperature after cooling is controlled to be greater than 0℃ and not higher than 4℃.

Pre-cooling is a plus.Large pastures can be equipped with plate heat exchangers to pre-cool the milk before it enters the tank, which reduces the impact of the temperature difference between the newly imported milk and the cold milk in the tank, and can also significantly reduce the burden on the compressor.In addition, the thickness and foaming quality of the polyurethane insulation layer determine the temperature rise rate during power failure or shutdown. It is also necessary to ask clearly when purchasing.

Direct Expansion VS Ice Storage Cooling

There are two main types of cooling systems for milk tanks: Direct Expansion (DX for short) and Ice storage (Ice Bank).

Direct expansion type: The refrigerant evaporates and absorbs heat directly in the evaporation plate at the bottom of the tank or on the wall of the tank, and the milk is cooled against the stainless steel wall.The advantage is fast cooling (it can drop to 4℃ in about 1 hour) and high efficiency; the disadvantage is that the compressor and power demand are large (generally three-phase electricity is required), and when the amount of milk in the tank is too small, the milk is easy to freeze near the evaporation plate.

Ice storage type: Freeze the water into ice during the milking interval (usually during the night valley electricity period), and use ice water to circulate in the tank jacket during milking to take away the heat of the milk.The advantage is that the compressor has low power and low requirements for the power grid, and can use night valley electricity to save electricity; the disadvantage is that the cooling is slower (about 2-3 hours), there are more maintenance parts, and regular descaling is required.

Table 2 Comparison of direct expansion type and ice storage type milk tanks

Comparison items	Direct expansion type (DX)	Ice-storage type (ice-bank cooling)
Cooling speed	Fast, it can drop to 4℃ in about 1 hour	Slower; approx. 2–3 hours
Compressor power	Large (about 1 horsepower/50 gallons·times)	Small (approx. 0.5 hp / 50 gallons per cycle)
Power consumption characteristics	About 0.9 kWh/100 lbs of milk, high efficiency	Approx. 1.3 kWh per 100 lbs of milk; however, off-peak electricity can be used, potentially lowering costs
Power requirements	Three-phase electricity is required, and the instantaneous load is large	Compatible with single-phase power; suitable for areas with weak grids or time-of-use electricity pricing
Power failure response	There is almost no cold storage capacity, and the milk temperature rises within a few hours after the power failure.	The ice acts as a cold reservoir, providing cooling for an additional 6–12 hours
Risk of icing with low milk content	Higher, less milk, easy to freeze locally	Lower
maintenance	Relatively simple	More components; requires periodic descaling
Typical application	Large and medium-sized pastures, sufficient three-phase electricity, the pursuit of rapid cooling	Small farms, off-peak electricity pricing, unstable power grids

Comparison of Brand New Milk Tanks and  Second-Hand Milk Tanks

Table 3 Comparison of brand new milk tanks and second-hand milk tanks

Comparison Item	Brand-new milk tank	Used milk tanks
Initial Investment	High	Low cost; typically significant price difference compared to new units
Hygiene and Compliance	Inner tank, welds, and polished finish are brand new; meets current hygiene standards	Welds and scratches may harbor bacteria; older models may not meet current regulations and certification standards
Refrigeration System	Compressor and refrigerant in optimal condition; high energy efficiency	Aging compressors, refrigerant leaks, and damp or degraded insulation lead to reduced energy efficiency and higher electricity costs
Seals and Wear Parts	Brand new	Components such as seals, agitators, and thermometers may be worn and require replacement
Warranty and After-sales Service	Typically comes with a 1–2 year warranty	Usually no warranty or limited warranty; the buyer bears the risk of breakdowns
Hidden Costs	Low	Costs associated with repairs, downtime, and risks to milk quality may outweigh the initial savings

Check List of Milk Tank Capacity Before Purchase

Before placing an order, go through this list item by item：

1.Did I use "peak daily milk yield" (rather than the average) as the basis for calculation?

2.Was the capacity calculated using the formula: "peak daily yieldxmilk collection interval (in days) x buffer coefficient (1.2–1.3)"?

3.Has sufficient allowance been made for herd expansion or increased yield per cow over the next 2–3 years?

4.What is the minimum amount of milk for this model?Will the output in the off-season be lower than it?

5.Can the refrigeration system reduce the full can of milk from 35℃ to 4℃ within 2 hours (meeting the regulatory requirements of 0-4℃)?

6.Does the power and stirring time of the agitator meet the requirements of ”stirring for at least a few minutes per hour"?

7.Can the size, floor height, ground load-bearing and passage of the milk storage room accommodate this tank and milk tanker?

8.Is the power satisfied (three-phase electricity, power margin)?Can you take advantage of the Valley Power policy?

9.Is it equipped with CIP automatic cleaning?Can the cleaning spray cover all the inner surfaces?

10.Does the thermometer, sampling valve, and metering device meet the requirements of the milk receiving party and regulations?

11.Does the manufacturer provide written technical parameters, warranty and after-sales service?

12.Have you confirmed with the milk recipient/dairy company their requirements for tank capacity, standards and interfaces?