Two basic procedures are used in North America for cleaning milking equipment
The standard cleaning procedure consists of four phases: pre-rinse, a chlorinated alkaline cleaning, an acid rinse, and sanitization
As discussed in Milkproduction.com’s article – Cleaning Milking Systems, Basic Practices, the perfect system for cleaning and sanitizing milking equipment would meet the following criteria:
- Remove all soils from all surfaces
- Kills/removes bacteria
- Non-corrosive to equipment
- Minimizes time and energy required
- Safe for humans: handling and food residues
- Safe for environment
In North America, two basic procedures are employed to clean milking equipment. The standard procedure is a 4-part process. An alternative process with only 3 components has been developed. The following paper will discuss each part of both North American cleaning procedures in detail.
Cleaning Procedures - North America
The standard North American cleaning program consists of four phases. These are the pre-rinse, a chlorinated alkaline cleaning, an acid rinse, and sanitization. The pre-rinse is warm, the chlorinated alkaline cleaning is done with hot liquid, and both the acid rinse and sanitizing phases are conducted under ambient conditions.
The alternative cleaning process used in North America has only three phases. In this procedure, the acid rinse and sanitization phase are combined. The result is a process consisting of a warm pre-rinse, a hot chlorinated alkaline cleaning phase and an acid sanitization at ambient temperature. The alternative procedure has an advantage over the standard cleaning process, in that it reduces time and water requirements.
Phases of the Cleaning Program
After milking, all milk contact surfaces must be thoroughly rinsed with warm water (105-110 degrees F). No re-circulation occurs. The rinse step removes most but not all of the residual milk film. Rinsing the milking system needs to be done promptly before milk film dries. The temperature of the rinse water is critical. If it is too cold, milk fat solidifies and sticks on surfaces. If the rinse water is too hot, milk protein denatures and sticks to surfaces. Denatured milk protein is very difficult to remove.
Chlorinated Alkaline Cleaning Phase:
Rinsing leaves some milk residues, making a cleaning phase necessary. During the cleaning phase, chemicals are diluted in hot water and circulated with force through the system to remove the remaining milk residues. Appropriate time, temperature, chemical concentration, and energy are required to successfully clean the milking system.
All commercially available cleaning products should have components that perform these standard functions, although they may vary in other ways. The chemicals involved during the cleaning phase include; alkali source, chlorine source, water hardness control agent, wetting agent (powder), and defoamer (powder).
Commercially available products can take a number of physical forms including; liquid, powder, tablets, and solid blocks. The ratio of alkalinity to chlorine may differ between products, as will the type and amount of water hardness control agent.
Stability is an important attribute of cleaning products. For liquids, the stability of the chlorine is critical. Caking of powdered products is another issue to consider.
Pipeline cleaning solutions are based on alkaline materials. Alkali breaks down the milk fat in a process known as saponification. The result is soap-type components that can be suspended in hot water and flushed out of the system. This process is necessary because fat is not soluble in water. Alkaline chemicals used in cleaning products include; caustic soda (NaOH or lye), potassium hydroxide (KOH), and other alkaline materials.
Chlorine is included in these cleaning solutions to attack proteinacious components of milk soil. Milk proteins are divided into two types; casein and whey. Casein makes up 80% of total milk protein. The remaining 20% is whey. Chlorine breaks down and removes protein material from surfaces. This is especially important if pre-rinse water gets too hot. Pre-rinse water that is hotter than 60 °C will bake milk onto a surface. Such cooked deposits can only be removed by a strong alkaline chlorine solution. Sources of chlorine include sodium hypochlorite and organic chlorine sources
Cleaning solution strength is determined by alkalinity and chlorine. Alkalinity is expressed as alkalinity or active alkalinity; which is alkalinity measured above pH of 8.5. The goal is to achieve a pH of 11.5 or above in the wash solution. The optimal level of active alkalinity depends on the size of the system being washed. Big milking systems with meters, sensors, and long milking times require highest levels of active alkalinity:1200-1500 ppm. Smaller, simpler systems with short milking times may use lower levels of active alkalinity (700-1000 ppm).
Chlorine is measured as ppm available chlorine in the wash solution. Typically, cleaning solutions provide 100-140 ppm available chlorine. Chlorine concentrations can decline as product ages or when stored at high temperatures. Using chlorine-containing products at lower than recommended levels can reduce protein solubility.
Water Hardness Control Agents
In areas where water is hard enough to reduce cleaning efficiency, water hardness control agents may be required. Chelating agents (STPP) tie up hardness (calcium and magnesium) on a one-to-one basis. The harder the water, the more chelating agent is needed. Thresholding agents suspend calcium and magnesium salts for a limited time (20-30 minutes). The amount of thresholding agent used does not change with the hardness of the water. Thresholding agents can handle a maximum of roughly 20 grains water hardness, although this is system and formulation dependent.
Following system cleaning, alkaline residues and mineral deposits are left on the surfaces and must be removed to prevent mineral film buildups. Typically a low-foaming acid solution is re-circulated through the system after cleaning. The acid neutralizes alkaline residues and allows them to be rinsed out. The acid rinse also dissolves minerals and removes them from the system. The resulting acidic condition (low pH) of the pipeline surface helps reduce bacteria growth between milkings.
Acid Rinse products are typically based on phosphoric acid. Blended acid products are also available; such products may use sulfuric, nitric, and phosphoric acids in combination.
Wetting agents/rinse aids
These materials are added to powdered or liquid, and acid or alkali detergent to improve performance. They are used in small amounts to achieve the desired effect. Proper selection of these materials can have a substantial effect on the performance of the detergent or acid. Wetting agents help the cleaning solution wet out surfaces and penetrate soils. Rinse aids help the cleaning solution drain from the pipeline and prevent mineral and soil deposits. Defoamers, as the name implies, control foam caused by the breakdown of fat and protein.
Minerals and Cleaning
Mineral deposits can lead to milkstone. Milkstone is the result of fat, protein and minerals depositing in several layers. Milk contains a number of minerals including; calcium, phosphorus, sodium, potassium, magnesium and chloride. Minerals in water may further add iron, manganese and other minerals. Mineral deposits require an acid detergent to dissolve them.
Sanitizing of Equipment
The PMO states that prior to milking, “all milk contact surfaces shall be sanitized with an approved sanitizer”. Milking systems may be idle for hours between milkings. Bacteria that survived cleaning and the acid rinse will grow between milkings, possibly leading to bacteria count problems.
Flushing the milking system with an approved sanitizer before milking kills and eliminates bacteria that may be present. This practice sanitizes the equipment rather than sterilizing it. Proper sanitizing helps reduce bacteria count problems. Typically chlorine or iodine products are used. Approved sanitizers in the USA (EPA regulations) are to be used without a potable water rinse.