Cooling milk immediately after milking keeps bacteria from multiplying rapidly. Holding milk at temperatures below 40°F (4°C) and above freezing maintains its excellent quality until it is processed for fluid milk or manufactured into dairy products. Each degree in temperature above 40°F(4°C) elevates bacteria counts and decreases the shelf life of finished products. Under PMO regulations raw milk sold to processors must be less than 100,000 standard plate count. All farms have the capability of producing milk under 5000.

Close temperature control, clean milk and sanitary equipment help many dairymen earn quality premiums and avoid penalties based on bacteria counts. Even though the regulatory limits are less stringent, reference PMO item 18r, ideal milk cooling systems on dairy farms should:

• Cool milk below 40°F (4°C) 30 minutes after the first milking ends,

• Hold the milk at 37-38°F (3°C), and

• Prevent temperatures from rising above 45°F(7°C) any time after four hours after the start of milking or during the addition of milk from subsequent milkings

This goal is more demanding than any state requirements of the national PMO (Pasteurized Milk Ordinance) recommendations but is more appropriate to meet today’s standards for consistently producing high quality milk.

Direct expansion bulk milk tanks, silo tanks and direct-load tankers using in-line coolers are currently popular.

Contrasted to cooling milk directly with refrigerant, one can use chilled water and circulate cold liquids through in-line coolers

Water or process chillers are common in processing plants and are increasingly used on large farms with high cooling requirements. Water solutions may include nontoxic solutions or propylene glycol to lower the freezing point. Solutions cascade over cold evaporator surfaces to bring coolant temperatures close to freezing. The chilled coolant is then circulated through in-line coolers, water jackets or other heat exchangers which keep the product separate from coolant.

In-line tube or plate coolers with cold well water allow for partial milk cooling, reduce the refrigeration load and conserve electricity. The coolant water should be utilized and not returned to its source. This coolant water may be used for some potable water purposes if it meets the criteria specified in the PMO and is allowed by the state regulatory agency. These heat exchangers also can be used with circulating hot water to help maintain high temperatures for cleaning milking systems.

Another type of heat exchanger recovers heat from the hot refrigeration gas. These heat recovery units effectively conserve energy by reducing the operation of fans, by reducing the heat radiated from condensing units, and by warming water to feed water heaters or livestock waterers.

This is an excerpt from the Dairy Practices Council’s Guideline #108, Proper Cooling of Milk on Dairy Farms. More information can be found at the Dairy Practices Council’s website: www.dairypc.org.