Miling Stainless

The role of nickel-containing stainless steel in milk production

December 21, 2016


Dairy cows can seem gentle creatures—and for the most part are. But with an average weight of 475 to 700kg, they can cause damage if they lean against barriers or piping and can pack a hefty kick or a targeted neck swing if irritated. To the farmer, strength and toughness to resist battering are important for housing barriers as well as  food and water dispensing equipment. And longevity, corrosion resistance against excrement as well as disinfection and ease of cleaning are also required. Cow manure is a beneficial fertiliser for gardens and fields and plays its part in biogas production but as slurry in farm buildings, it does have its drawbacks.

At the milking parlour, hygiene becomes paramount. Daily washing down, sterilisation of pipework, milking equipment and tanks are carefully carried out. Milk is monitored for bacteria counts and if it is not very strictly controlled, can be rejected. For a market in which profits are narrow, problems such as mastitis and milk contamination can be catastrophic for the farmer. As herd numbers increasingly grow and there is a move from herringbone and rotary parlours towards even more sophisticated robotic systems, the choice of materials becomes more selective too, for camera-controlled milking arms, cabinets for data display control panels and ancillary equipment such as floor plates to avoid slipping, parts of foot-trimming crushes and ventilation blowers and ducts.

Stainless steels have been successful in transforming the dairy industry for over 60 years. They have ideal strength and corrosion resisting properties for the range of required applications and form the core equipment used throughout. Grades used are primarily Type 304L (UNS S30403) and Type 316L (S31603) stainless steels although duplex alloys are now being used under more exacting conditions. Stainless steels are hygienic because they have smooth bright surfaces which are eminently cleanable and can remain so with time. Strict standards of hygiene are therefore possible at every stage of its use. Stainless steel behaves neutrally and does not alter the taste or smell of fresh milk or milk products nor does it react with the lactic acids formed by fermenting milk.

The composition of fresh milk can vary widely between different breeds and during different stages of lactation but typically contains about 87% water. The remainder consists of solids in the form of lactose (carbohydrate), fat, protein, and minerals. The pH normally lies between 6.6–6.8. Milk arrives from the cows udder at 35 °C. It is very quickly chilled down to 4–6 °C to prevent bacterial growth, and is kept in tanks usually equipped with stirrers or agitators to await collection. Heat exchangers are an important part of the dairy industry for cooling and heating, and are used to extract the heat from the raw milk. In some cases the heat is further used, for example in pre-heating wash water or space heating. Stainless steels are also used for the truck mounted milk tanker vessels which transport the milk from the parlour tanks to factories for further processing. Whether the milk is pasteurised for drinking, further dried as milk powder or goes on to make cheese, yoghurt, butter or ice cream, stainless steel equipment is necessary to  meet very strict hygiene standards.

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