How It Works: Cream Separator
There were a lot of things I looked at with wonder while growing up on a farm in Kansas. One of the most intriguing was the cream separator. Every morning and evening, my parents poured the produce from 20 cows through the separator, which instantly divided cream from milk. The cream flowed into cans destined for town; the milk went into buckets that were dumped into a hog trough.
By the time I was in high school, though, the cream business had disappeared, along with any use for the cream separator. From that point on, area farmers adapted to the market for whole milk or got out of the dairy business. It’s no surprise, then, that most people today have never seen a cream separator work, let alone know how it works. Simply put, the separator uses centrifugal force.
Putting gravity to work
In its raw form, milk contains a mixture of large and small butterfat particles held in suspension because they weigh less than the other parts of whole milk. It’s not unlike drops of oil mixed with water.
In both cases, lighter material rises to the top when the mixture is left standing. Consequently, when whole milk sits for some time, the heavier skim milk gradually settles to the bottom of the container, while the lighter butterfat rises to the top.
The earliest methods of cream separation involved gravity. In one early method, milk was poured into shallow pans (2 to 4 inches deep) known as setting pans. The pans were placed in a cool, clean room for 36 hours, allowing the cream to rise to the top. At that point, it was skimmed by hand with a tool called a cream skimmer.
This method made it difficult to handle large amounts of milk. As much as 30 percent of the cream was left behind. What’s more, if the milk wasn’t properly stored, the cream could easily sour.
According to early calculations, if a cow produced 300 pounds of butterfat a year, the shallow pan system left at least 30 pounds of production in the skim milk. At 50 cents a pound, that 30 pounds of butterfat had a value of $15. Consequently, a dairyman with a herd of 20 cows, whose average annual butterfat production was 300 pounds each, would suffer an annual loss of $300 — more than enough to pay for a “modern” cream separator.
Later methods of cream separation involved the deep-setting method. Milk was placed in tall cans (often referred to as shotgun cans) placed in tanks of cold water. Measuring about 8 inches in diameter and 20 inches tall, the cans typically held about 4 gallons. The small diameter of an individual can allowed the water to cool the milk quickly, while its height put gravity to work, resulting in more efficient separation. Again, the cans sat for several hours before the cream was dipped off the top.
According to Doug & Linda’s Dairy Antique Site, “Some cans had glass windows to see the cream line and a valve at the bottom to drain the skim milk. In the deep-setting method only 5 to 15 percent of the cream was left behind in the skim milk. In their 1897 catalog, Sears, Roebuck & Co. sold these cream setting cans for 55 cents (without a glass sight window) and 60 cents (with the window).”
Another gravity separator, the Marvel, used water to dilute the milk and speed separation. According to the website, once the cream had risen to the top, the skim milk and water were drained out through a valve at the bottom of the can. Two glass windows allowed one to see the cream line.
Applying centrifugal force
It wasn’t until the mid-1800s, when inventors first applied centrifugal force to the separation of milk, that dairy farmers could look forward to a better way of harvesting cream. The first such machine, dating to 1864, is credited to German inventor and brewer Antonin Prandtl. His machine consisted of a vertical axis rotated by a crank handle on which a crossbar containing two small buckets was mounted. The buckets were filled with milk and whirled rapidly. The cream, being lighter than the other parts of the milk, gradually moved to the top. Once the machine was stopped, the cream was skimmed off much as it had been with gravity systems.
The idea of separating cream from whole milk by whirling the milk did not originate with Prandtl, however. It’s believed that separation of liquids by centrifugal force was first used by the Chinese, who separated juices and oils from fruit pulp by whirling the crushed material in a hollowed gourd at the end of a cord.
In 1870, the Rev. H.F. Bond of Massachusetts invented a similar centrifugal machine. Instead of buckets, small glass jars held the milk. Neither technique allowed production of more than limited quantities, making it unattractive to would-be commercial producers.
At an 1874 dairy exposition, German engineer Wilhelm Lefeldt commanded attention when he demonstrated his separator concept. With a nod to what would become the modern separator, his innovative device separated 220 pounds of milk in about half an hour (but it required an additional 30 minutes for the drum to cease rotating, at which point the skim milk was drained off). Lefeldt won a patent for his design Sept. 25, 1877.
The de Laval influence
About the same time, the idea of centrifugal cream separation caught the attention of Swedish engineer Carl Gustaf de Laval. de Laval’s invention, a machine through which milk flowed continuously, changed the dairy industry worldwide. His continuous centrifugal cream separator discharged cream and skim milk separately, while milk was fed non-stop into the machine.
Over the years, de Laval enhanced his original design. For example, his original separating bowl was a hollow cylinder containing wings to keep the milk rotating with the bowl. However, in 1890, his company developed the “Alpha disc” bowl, in which a number of conical steel discs were placed within the bowl, one above the other, spaced slightly apart. Fed into the center of the bowl as before, skim milk was separated from cream with less difficulty than in the hollow bowl, where the milk and cream were allowed to form a solid mass.
As centrifugal force was applied by a unit spinning at 6,000 to 8,000 rpm, the cream was delivered near the bottom of the bowl and gradually passed upward from the inner ends of the discs nearest the cream outlet. Skim milk was similarly passed upward during centrifugal motion, but because of its density, it passed outward through the spaces between the discs in thin sheets and was forced to the outer ends of the discs. In this cavity the skim milk passed toward an outlet through which it drained into a separate bucket or milk can. Unprocessed milk, meanwhile, was fed into the separator at a constant stream from a vat positioned above the bowl.
Progress through technology
From the start, the continuous flow separator offered farmers a huge advantage. In contrast to gravity flow systems, a well-adjusted centrifugal cream separator left less than one percent of the cream behind in the skim milk. Centrifugal force also produced a filtering effect that removed most of the foreign matter in the cream.
Most important, though, farmers could milk more cows and increase their profits, since greater quantities of cream could be separated in less time. Within a matter of months, cream separators were being imported to the U.S. — primarily from Sweden — and farmers began to expand their herds.
Cream separators made their first appearance in the Sears, Roebuck & Co. catalog of 1896, while Montgomery Ward & Co. listed them as early as 1894. Sears sold the Young America cream separator, rated at 300 pounds of milk per hour, for $97, while Montgomery Ward offered the Safety Hand separator (with the same rating) for $125.
As noted on the Dairy Antique Site, cream separator manufacturers flourished in the early 1900s and prices dropped significantly. By 1902, Sears advertised its own Sears cream separator in 250-, 350- and 500-pound/hour sizes. The 350-pound/hour machine was priced at $63.75 (about $1,677 today). That was the start of the Sears Economy cream separator line. Cream separators continued to appear in Sears and Wards catalogs into the mid-1950s.
Refining an industry
In 1879, in honor of his invention, de Laval was presented a silver medal by the Royal Agricultural Society of England. Shortly thereafter, the King of Sweden presented him with the cross of the Order of Vasa and made him a Knight of the Order of the North Star. In 1886, de Laval became a member of the Royal Swedish Academy of Sciences, which presented him with a gold medal in 1892. He was made an honorary member of the Agricultural Academy of Sweden in 1896.
Although de Laval’s invention separated cream from milk, the dairy industry still faced a pressing problem: determination of butterfat content in both cream and skim milk. In 1890, Dr. Stephen M. Babcock, an agricultural chemist at the University of Wisconsin, discovered a simple test that determined with great accuracy the percentage of butterfat in whole milk, cream and skim milk. (For more on milk testing, see Growing Up with the Milk Tester and Milk Scales) Today, it can easily be said that de Laval and Babcock changed the dairy industry worldwide. Although cream separators have virtually disappeared, except for use on a few hobby farms and specialized dairies, de Laval’s invention alone was once estimated to have saved the dairy industry as much as $35 million worldwide. FC
Tharran Gaines is the author of five books on antique tractor restoration and writes a variety of materials for AGCO Corp. He is also a contributing editor to AGCO Advantage and Massey Ferguson Farm Life magazines for AGCO. Email him at firstname.lastname@example.org; online at Gaines Communications
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