centrifugal cream separator how it works | The Green Lever - Using minimal resources for maximum quality of life

Fresh cow’s milk comprises between 85%-90% water and less than 5% fat (cream). Historically, the valuable cream was obtained by leaving the milk to stand in crocks or earthenware containers in the dairy. The less dense fat globules in the milk would rise to the top of the containers and after a period of up to 24 hours, the cream layer could be skimmed off the top. Later refinements of a tap, fitted to the bottom of the container, allowed for the denser skimmed milk to be drained, leaving the cream behind.

Heritage breed Normandy cows - La vache normande

There was always a considerable amount of cream left within the skimmed milk and this, coupled with the chance of contamination or souring during the long settling period, was a reason why the dairy side of the farm was never a large proportion of the enterprise. This all changed with the introduction of the continuous cream separator in the last half of the 19th century. Thereby allowing small farmers and homesteaders/smallholders to make cream and butter on a viable marketable scale.

The Separator

A page from an original manual - from 'spiritedrose' blog link below

Most of us today will have seen the centrifugal effect, laundry sticking to the walls of the washing machine drum during the spin cycle is a good example and it was the utilisation of this effect which led to the development of the cream separator. Originally containers holding the full-cream milk were spun around a vertical axis. The centrifugal effect on the milk meant that the less dense fraction (the cream) would separate from the main body of liquid and once brought to rest could be skimmed off. Although separation was faster it still meant that the milk had to be processed in batches.

Carl Gustaf de Laval refined the centrifuge idea to create a machine that continuously separated the cream from the milk. His design had a covered bowl which rotated around its vertical axis. Inside this bowl were assembled a stack of conical discs. The bowl, its lid and the discs were all mounted on a driven shaft.

Traditional Cream making on an organic farm

The cream is used directly from the cow so it is run directly into a churn to avoid it being cooled in the bulk tank.

The Separator in Operation

Nowadays it is usual for an electric motor to spin the bowl but originally many of these machines were turned by hand. An exceedingly high gear ratio means that the hand cranking speed is increased to a bowl speed of 6 000 to 8 000 rpm. The consequence of this gearing is that it is very hard to start the turning, you can hear in the film Mickael joking that my face was going redder, well it was hard work! Nowadays ‘soft start’ electric motors obviate the need for any human musclepower.

The milk is poured into a header tank above the the bowl and enters the bowl via a spigot. where it experiences the centrifugal effect causing the rapid separation of the cream from the milk.

It is interesting to note the configuration of these discs. In the case of the separator in the film (at the end of this post) all of the discs excepting the top one have four 1cm diameter holes near the large central mounting hole. When these discs are assembled these holes line up with those in the adjoining disc. The purpose of these holes is to allow the passage of the raw milk, fed from the bottom of the assembly. It thus means that each interstice between the discs has fresh milk entering it, the denser fraction of the milk is flung to the wall of the disc and thence to the disc perimeter, leaving the cream to rise and pass through the cream outlet.

(A fabulous vintage advert from 1909 Sue posted to her Pinterest boards. It comes from vintageproductads.com)

Although it takes 20 litres of milk to make one litre of cream the farmer is left with two usable and/or marketable products, skimmed milk and cream. Furthermore, the cream can undergo another transformation and be made into butter. Every litre of cream yields 500 grams of butter and again there is no loss with two separate products being created from the process, butter and buttermilk. As people like us are returning to the land and self sufficiency, these sort of machines are proving invaluable and the great thing is they are still about. Many people using or finding them as flower baskets or garden ornaments are now refurbishing them back to working machines. There is also still the possibility of getting spare parts and there are people out there, including on the internet, willing to share knowledge in maintaining and rebuilding these separators. I will put some useful links at the end of this post. It is very pleasing to me that these wonderful pieces of engineering are experiencing a renaissance after so many decades of neglect. It is particularly poignant for us because Gustaf de Laval, although born in Sweden was from French ancestry and Laval is just over the border from here in the next county.

The Normandy Cow

The Normandy is the ultimate sustainable cow because she has only been bred for one thing, to produce high quality creamy milk from grass pasture. When the Vikings came marauding around Northern Europe they were well equipped for a long stay, even bringing their own livestock with them and began farming here in the 10th century. The descendants of these cattle, like the Normandy, can been seen today in the hardy ancient breeds on the Islands and Mainland of Scotland and Ireland and the coastlines of Northern France. Some 5,000 years ago a mutation occurred in the milk solids of dairy herds, in particular in the beta-casein chain of amino acids at position number 67. Cows without the mutation are known as A2 and those with the mutation, such as the Holstein race, are called A1. There is a great deal of information on the internet in particular from the Weston Price Foundation on the health implications of A2 v A1 milk.

A victim of war like the cream separator, the race of la vache normande was virtually wiped out in the battles of Normandy during WWII. It has been a labour of love by individual farmers and enthusiasts to get these beautiful animals back into their countryside. A crowning achievement recently, was the inauguration of an AOC Camembert made exclusively from la vache normande cows' milk. With the ever increasing back-to-the-land movement here in France, the Normandy and her sisters, such as La Pie Noir and the Froment du Léon have returned and to stay.

..and now if you'd like to, sit back and watch the film: